Hi. In general Imaging/guiding should be below or equal to 5 for good and accurate guiding. Long focal length guide scopes are surely more precise and accurate. However mount payload capacity should not be exceeded and this can happen with a heavy guide scope. I have two guide scopes, namely 169 mm and 240 mm focal length scopes and two guide cameras, namely the zwo ASI 120 and 290. Both mini versions. Depending on my main scope/camera combination, I use the appropriate guide scope/camera/Barlow combination to be always below a ratio of 5.
Doug, I'm almost certain that the long vs short focal **ratio** is less relevant when compared to the long vs short focal **length**. From the research I've done, I've found that you want whatever focal length gets you to within twice the pixel scale of your imaging focal length. For example: If your're imaging at a pixel scale of 1 arcsecond, your guide scope should not exceed two arcseconds per pixel. With many of the guiding programs we have today, PHD2 being the most commonly used one that I know of, sub-pixel guiding is possible because the centroid of the guide star can be computed to be 'between' pixels. This calculation, along with proper guider calibration, can allow the guiding program to correct for sub-pixel guide star movements. The 2:1 pixel scale ratio is important because at higher ratios, the sub-pixel adjustments may become too small to correct for errors that may show up in the imaging camera. I've only ever successfully guided a handful of times myself. And those times that yielded the absolute best results for me were when I was guiding 1:1. I will be buying a new guide scope for my newest telescope (A 10" Meade LX50) - and even with a 0.63 reducer my pixel scale will be 0.71 arcseconds per pixel using my SBIG ST-8300. Therefore I need to get my guide scope pixel scale as close to 1.5" per pixel as possible. An Orion ST80 with a 2x barlow lens and the ASI174MM camera will get me to 1.5" pixel scale - and I should be able to benefit from the sub-pixel guiding algorithms from my auto guiding program.
Thanks Mitchell! I haven't heard this theory yet about 2:1 Pixel scale. Thanks for explaining that to me. Now, if I use your theory, and compare my "bad" experience to my "good" experience...let's see how it adds up: Using this formula for arcsec, Victor posted this in the comments earlier: arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) "Good" AG arcsec was 1.92 "Bad" AG arcsec was 8.04 Camera was the same in both tests, the Scope used was an Orion 80EDT using a 0.8 Focal Reducer 480 * 0.8 = 384 Focal Length 5.5 Pixel Size 2.95 = (206/384) * (5.5) Well in my case that would put "Good" AG @ 1.92 to Telescope @ 2.95 "Bad" AG @ 8.04 to Telescope @ 2.95 I always have great guiding! So with your theory, please correct me if I misunderstood you... If my camera is 2.95 and twice that is 5.9, my AG is registering 1.92, it's well below the 5.9. I can't seem to find a formula that is universal. I have repeated reports of people succeeding when close to 2.0 on the AG, but, I don't know about their main imaging setup. Very interesting and I appreciate you giving me more info for thought. Thanks again! Doug
Doug, I think you understood and explained it back to me well enough. I do think that the reason you cannot find a universal formula is because everyone guides differently. Two people with identical optical tubes, guide scopes and cameras may use two different programs that calculate the centroids of the guide star differently. This will result in different guiding. The same two people may agree to use the same software the next night, but one telescope is not properly balanced. Again this will result in different guiding. In doing a little more research on this topic after your video, I stumbled upon this website, which has a very interesting calculator that seems to support your "Bad" AG setup as likely being a good guider... Check it out, play around with it. It goes completely against my 2:1 rule of thumb - but I'm always open to try new things when presented with compelling evidence. I may try this out as well with my 10" some day. www.wilmslowastro.com/tips/autoguiding.htm
Wow, that's really interesting. No one can agree on a "perfect" setup. In my case, I just grabbed a barlow, and it worked better. So while it "may" work better for me, it may not work better for other people. Of course, if it's working, leave well enough alone! I thought I'd throw out my finding to other people and see if anyone else could/would benefit from results. I never thought AG would be so complicated! I've been lucky and I can AG 30 minutes subs no problem when I want. And that's with an Atlas Mount. I also use 2 second exposures in my AG routine. Thanks Mitchell for bringing up more possibilities in this discussion, I appreciate your feedback. Doug
Interesting question, have you changed the settings in the guiding software before you used the shorter guidescope? I used a 53mm aperture guidescope at f 3.6 at 190mm and tested up to 10 min exposures imaging with Skywatcher ed80/600 with good guiding 0.5 to 1 arcsec/pixel, using Zwo 120MM-s monochrome camera, and having an image scale of 4 arcsec/pixel. I recently tested with success imaging 4 minutes using a Ritchey Chretien 6 inch telescope 152/1370mm, at 1370 mm focal. Have to research more on this subject, but I think longer focal length for the guidescope is more critical when you use longer focal lengths with your imaging scope, maybe from 1500 higher, a good compromise between focal length and focal ratio might be needed so you have not only a better image scale arcsec/pixel, but also a good signal to noise ratio
Hi GAM, No I didn't change the software settings. Other people have made the same comments. My mistake. I do enjoy the longer focal lengths. I have taken in the past 30 minute exposures with no problems. My refractors do not have long focal lengths. Thanks for commenting and sharing your advice. Doug
@@Myastroimages with pleasure. I comented also on a video of yours some time ago you had the wrong setting for the youtube kids and advice to change to the one that is not for kids so you get monetized and not having other problems because of the wrong settings. My channel is smaller i have started to grow my channel one year ago but growing was not so fast but hope will be better.
@@Myastroimages I think it will for my new EdgeHD 8". I'm putting a WO 50mm (200mm FL) for guiding, and I think a Barlow will put it in the perfect ratio of "within 1 to 5 ratio". 2000 / 400 = 5/1
@@ryanmichaelhaley 200MM / 50mm = F4 Native EdgeHD 8" 2032mm / 203 = F10 Native If you use a 2.5X Barlow, that would make your guidescope F10 Much closer match to your scope's native F10 Hopefully when you try it, you'll see a noticeable improvement!
@@Myastroimages I hope so, and I heard that you want the focal length of the guide scope to be at least 1/5th that of the primary scope. As long as the Barlow puts the guide scope past 400mm, then it's perfect for the 2000mm EdgeHD 8.
There is nothing wrong with either setup. Your issues more than likely had to do with reconfiguring your guiding software with the correct focal length settings of the new scope. That being said, guiding with a scope that complements what you are imaging with will help. If you are imaging with at 2000mm+, a longer focal length might perform better.
No guiding prob here ... but, in my travels I've read that guiding software often doesn't play nicely with sharply focused stars. There can be too steep a 'cliff' in dropoff of brightness at the edges of a sharp pinpoint star. So if using finderguider / short focal length / wide field of view / low mag guidescopes, it can help guiding by defocusing a bit .... gives the guide software more pixels 'width' for the star for it to find the centroid of. Like I said, I don't have problems 'falling' off the guide star, but I have read the above comment a few times now (when I've been searching for info on how to read and use the DEC/RA charts in the guide software and how to use that to adjust all the other many options in the programs!). Congrats to you for the out-of-the-box solution though! Throw a barlow in, thus avoiding having to spend $ on longer FL guidescope, dovetail, rings, etc which then may flex more, weighs more on your mount, maybe even forcing a mount upgrade(!), etc. So great vid. Thanks for posting that up.
HI Carl, Yes, I've heard of soft focus ag stars too. I don't do a fine focus on my AG. Thanks for sharing your AG details and I appreciate the comments and thumbs up! Doug
I wondered about the barlow... I have a 2x barlow I never use, and as yet havent tried with my guide scope. Will give it ago.... when it stops raining :)
Scope is best used at its native FOV , cant be bigger , can be smaller but if you decrease FOV to get more magnification then you lose aperture for you are wasting the rest of it and that means lower resolution ,so for guiding you can use Barlow to get that F ratio up to F10 , but for imaging , if you move it down goes you quality . Its the way she rolls
Hi, I struggle to guide with my 50/183 guide scope. I am really leaning to its short focal length to be the culprit. I'll try inserting a barlow. Thanks!
Hi Doug I have an Orion 110mm f6 & use the 60mm guidescope I have had good results using phd & my canon dslr I have only started in this field but am happy with results so far I really enjoy your videos Looks like your viewing area is fantastic I'm in very urban environment in Sydney area in Australia Keep up great work Cheers
Thanks Rider! I appreciate your comments and views. You know, one of the best things to do...is to leave well enough alone! If you Autoguiding is working, then that's great! Just keep it in mind. I was surprised when I found a barlow helped my AG performance. When I travel to my darksite, The skies are good, but, it's a struggle to find dark skies as you know. Sydney must be challenging for LP. You should try traveling to a dark site if possible. It's worth the extra effort. Doug
Thank you...good job thats the kind of stuff I need to know..I'm just starting...but a quick learner and this very issue was a concern...I'm in Subscribed
Thanks Maximus. There are differing opinions out there as you know. Even in the comments here some people were suggesting no problems with a F/3.6 guide scope and suggested I try adjustments in the imaging software. Good luck on your new adventure! AP is very rewarding. Doug
Due to bad situations in life, I am not currently able to get out and do any kind of astronomy work. In fact, I'm going to have to replace much of my stuff at some time in the future. So, I can't test this, but I have to wonder, what are you using as your guide software, and is it properly configured for your guide scope? More specifically, are you using something like PHD2 and did you set up the focal length correctly in the software for the scope? I realize this was two years ago, but I'm now curious as to how that works for you.
Hi Gary, Yes, other people have mentioned here too about software settings. It was very easy for me to try both long and short focal lengths. I'm probably imagining this, but, wouldn't you think a more narrow view would be more precise than a wider view? Anyway, I know it works for me. Each person often finds the best option for themselves. I hope your situation in life hasn't deterred you from trying. You'll have to be creative and I'm sure you're very creative if you've tried this hobby. Good luck! Doug
@@Myastroimages Doug, from the gurus over on Cloudy Nights, it's more about image scale and the camera you're using. Honestly, I don't understand any more. I had an Orion SSAG setup, and that worked pretty well (considering I have A Celestron AVX).
i've been using a 60mm, 240mm focal length, f/4 guidescope successfully through PHD2 for a few months now using a zwo asi120mc and guiding camera. Did you create a new guidescope profile on PHD2 (or whichever guiding software you're using) for the 60mm? I wonder if you may have kept the the same profile and when the specs of the 60mm/barlow combination got close to the larger guidescope specs your guiding software began working as before.
Hi NoNo, No I didn't create a profile. I use MDL. But, I've never created a profile before for AG. It would probably help. Thanks for the suggestion! Doug
Thanks for this video and the informative comments discussion. I have been having issues with my Orion 60mm F4 guide scope so will give it the Barlow treatment next time out. I have been using the newer LPI-gc camera and PHd2.
Let me know if it works for you! The comments from other people have been great. Victor explained a formula and it seems to work. arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) It would be an interesting comparison if it works for you. While there isn't a perfect Arcsec/pixel size for AG, it seems 2.0 is the magic number. Mine before was 8.04 and after 1.92 arcsec/pixel. The 1.92 worked well for me. Doug
Oh man have I had problems with the shorties. I have the Orion guide scope and it is just horrible. I constantly lose stars and PHD is always jumping around when I check back. Adding a barlow is a neat idea. Good thinking!
Yes, that was happening to me too, losing stars, and bad tracking. With the Barlow I noticed an improvement. If you're having the same problem, get any old cheap barlow, and give it try. I think you'll be satisfied with the results!
Did you need to use an extension to get your 2x barlow to reach focus? I use the Orion 50mm with the Orion SSAG giving me about 6 arcsec/px. Haven't tried my 2x barlow yet. Waiting for clear skies. Thanks for the info!!!
its a good job i watched this guide scope is on my list its just after the Crawford focuser i need first for my ar90mm x900mm bresser scope the one i got with it was mediocre at best it's worshiped and prayed to every night :) good tip i was going to get that exact one 60mm in a few weeks time
I use a 60mm guidescope on my 9.25 SCT, F4 Astrograph and even on my Canon 300mm f/2.8 wide field setup (which I typically stop down to f/3.5). I've had good results with all of them. My main issue is differential flexure on my SCT. Already have plans for moving to OAG on it soon. Doug, you didn't really specify what "problems" you're having. When you say problems, are you talking about your guiding error? Weird star shapes?
My bad, you're right, I should have explained my "problems". What was happening is I was losing tracking. It would ride along for a while ok, then I think wind or atmospheric turbulence would cause it grab another star. So the best way to describe the "problem" is not holding a single star to track with. Reading some of the other comments, there is a formula that seems to work. In this short review, it seems Arcsec/Pixel close to 2.00 works best. When I have good tracking on the long focal length scope, I had 1.92 arcsec/pixel. Another person reported good auto guiding at 2.07. arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) It would be interesting to hear what your Arcsec/Pixel results are for your AG.
Hi Doug, this could explain the formula a bit: The guide software will only send a correction pulse to your mount when it detects movement of the guide star. To calculate an accurate star position, the light from your guide star needs to be spread across multiple pixels on your guide camera sensor. When the guide scope's focal length is too short, all the light from the star will fall within a single pixel and it will only move to the next pixel after a large tracking error, so your guiding will be bad. The formula is useful for comparing the difference in image scale between the guide camera and imaging camera (see the other comments).
For my experience, some guide problems are correlated to seeing condition and short focal lenght is better than longer... If the mount have not big meccanical problem and is good polar aligned, the seeing are the big problem... The guide star "dance" in the guide ccd and the mount are not able to guide too many correction guide pulse... I take photo with RC 1500mm focal lenght and guide with 700mm with binning 2 ccd guide (same effect of 350mm guide lenght)
I have a very good quality 80mm fl 7.5 refractor for imaging that I will use as a guide scope for my 100mm refractor...no problems....maybe because it's pulling in brighter star images? I do remember an equation that looks at several parameters to suggest a proper Gide scope for any given imaging scope....as I recall one of those parameters was focal length ....
Thanks Human! I'll bet there is a setting. Seems like there are so many settings under settings that are nested settings, sometimes they're hard to find. All the best! Doug
I think there is a formula for optimal guide scope fl and speed based on your imaging scope and camera. intuitively it helps with higher mag if you have good seeing and remember fewer stars to pick from. Otherwise there's other things you can do with binning and such. I think the idea is get it close to optimal without a lot of moving parts for flexure.
I've never seen this formula, but, I'll bet you're right. I've never tried binning. I just found this interesting when I saw the results. Took what I had and gave it a try. I like the longer focal lengths!
I'll try to find it. A fellow told me at one of the recent star parties cause he saw my set up. I know Adam and Co at the Astro Imaging Channel might have covered it. BTW I watched ALL your how to videos. Helped me over the years. Marty
Victor commented below about the formula: arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) When I calculated my setup I was 1.92 Arcsec/Pixel and Victor was 2.07. So I'm guessing anything close to 2.0 is good. I appreciate the loyal views and comments Marty! Doug
Hi Doug As the old saying goes " if it ain't broken, don't fix it! " Yes I agree with viewing at dark site. I'm hoping to image with dslr in US this coming September, as I'm taking family on holiday to US We will be traveling thought California, Oregon,Washington & then through Utah & Arizona I have been researching dark site so I can use dslr for nightscapes. Keep up the great work Cheers
Which guide camera are you using Doug? I'm using a 50/205 mm guidescope with an ASI120MM camera (3.75um pixels) to guide my 80 mm f/4.8 refractor. That's a resolution of 3.77 arcsec/pixel for guiding, while the main camera (ASI1600MM-C) operates at 2.07 arcsec/pixel. If you're using something like a Lodestar X2, which has much larger pixels, you will need a longer FL guidescope. Here's the formula for calculating your pixel scale: arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
Hi Victor, I have an older Lodestar AG camera. The specs are "CCD Full resolution Pixel data: Pixel size: 8.2uM x 8.4uM, Image format: 752 x 580 pixels" So, using your formula, BTW, thanks for formula. 1.92 Arcsec Pixel = (206/900mm) * (8.4) , So that matches closely to your 2.07. I guess you're saying the best results are when your Arcsec/Pixel are close to 2.00 +/- ? Thanks for explaining it! All I knew is that it didn't work with the shorter focal length. Since my Lodestar has a larger pixel size, that explained why it was happening! Doug
Modern guide software such as PhD2 can calculate the guide star centroid with sub-pixel precision. So the image scale from your guide camera can be larger than the image scale of your main camera, up to 3-4 times. In my setup, the difference is 3.77/2.07 = 1.8 so that's well matched.
Thanks Victor for all your help! Many other people have commented about poor guiding and it looks like it's due to the wrong Arcsec/Pixel size. The formula you provided is very useful to understand where you're at now and where you should be. Software may be able to accommodate for other configurations like you pointed out, but, many people do not know or understand how to use the software. I had no idea about this formula, all I did was start grabbing parts, and it worked with a barlow! But now with your formula, it will back up my findings. I think this deserves a follow up video to explain your formula. Thanks again! Doug
True Nathan. I find the OAGs are a little more difficult and I like easy. Who knows, maybe one day I'll take an OAG. Thanks for the comment and watching. Doug
check ur FL in PHD if ur using it... that makes a big diff.. if u have a 162fl and ur phd is set to 300mm.. mmm guess what.. tho.. i might try a 2x barlow to see if it helps for myself setup... any little thing that gives a few secs more of good guide is worth a go ..
I have used a barlow on my Skywatcher Startravel 80 guidescope to use with a Synguider. Guiding software like PHD have the ability for subpixel guiding, but the Synguider lacked this ability, therefor I had to use a barlow with my guidescope.
Good to know. The more I'm reading comments here, there seems to be a formula, but, I haven't found the ideal calculations yet. All I know, just like you found, a barlow helped. Thanks for commenting your solution!
Hey matey, let me trump everyone and tell you that I've been guiding (5 - 8m subs) using the humble 30mm guidescope which has a FL of only 130mm with my SCT reduced from 2032mm to 1422mm FL without any issues :) mind you, I'm using the smaller chip for my guider which is the QHY5L-II mono camera
Hi Ahmed, Interesting! Would you mind telling me your Arcsec/Pixel size? Further discussion has uncovered this formula for your Autoguiding Setup: arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) People so far that have had good success guiding have reported approx 2.00 Arcsec/Pixel. Since you've have great success, I wanted to see how you compared using this formula. Thank you! Doug
Did you actually calculate what would be needed for good guided main images and your telescope? It has to be in a certain range for it to work with the main scope and depends on focal length, sensor pixel size etc. I use the calculations to choose my next guider and/or guidescope.
Hi Vincent, Victor commented on a formula. arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) When I take that formula and apply it to my scope, my arcsec/pixel = 1.92. I don't know the ideal range, but, Victor says his was 2.07 on his rig and mine was 1.92...so I'm guessing the the correct range is close 2.00 arcsec/pixel. Do you have any suggestions for the ideal Arcsec/Pixel for Auto guiding? Doug
Astrophotography Tutorials Indeed! So you can calculate that for both guide- and main scope, then the value of the guide scope should be lower than 4x the number of the main scope (edited and corrected)
Hey Doug! Thanks for the many great videos. I have saved a lot of time and money thanks to them. Where im at in astrophotography is, that i think I should ditch my typical guide scope, and use a off axis guider. ( In my head) that would eliminate all flexure and I could find a guide star in my wide field of view. But..... THE INTERNETS, says I should use an oag with a long focal length scope. like a sct. Am I missing something?
Hi John, I'm glad you've learned a trick or two to save some money. There is no rule about anything in AP. Many times it's people who try new things that discover better ways. The OAG isn't for the faint of heart. There is a lot of tweaking needed to make it work, plus, an OAG gives you a very tiny area to pick up stars. If you do decide to look at OAG, Chris Gomez did a video for me a while ago explaining how to set one up. ruclips.net/video/yN9WZ7koeks/видео.html It's worth taking a look at, especially the helical-focuser. I appreciate hearing your comments about the videos, it makes it worth the extra time and effort. Doug
I learned something new! Thank you Maciej for letting me know about Multi-star guiding. I've never tried that before. What software do you use for Multi-star guiding? Do you see better results using Multi-Star Guiding?
With my 9x50mm guidescope I have never succeeded with guiding and always received the message " star did not move enough" when calibrating with PhD2. Best idea is either an 80mm telescope or as you have found a 3x barlow.
Hi Peter, Yes, after reading more of people's comments in this thread, there are mix results...Some people have no need for a barlow and some people do require a barlow. Apparently there is a formula. arcsec/pixel = (206 / focal length in mm) * (pixel size in microns). Getting close to 2.00 arcsec/pixel seems to the magic number. Mine was 1.92 and another had 2.07 with reported good results! All I did was try what I had on hand and without the formula, I found a 3X barlow worked best. But, using this formula would probably work too! Doug
That means with my guider as the formula puts my setup as 9.38 without any barlow so is this too much which I guess is because it means I have 9.83 arcsec/pixel. Wow.... I use a lodestar with 8.2 microns per pixel. Trust me to expect too much of PhD2.......
Let me know What happens Peter! I think once you get your arcsec/pixel closer to 2.0 you'll see an improvement. The formula is very helpful, but, I haven't seen the "good Number" to hit. Right now, I'm guessing 2.0 is the magic number, but, If can confirm, that would be 3 people with good guiding at 2.0. Thanks Peter! Doug
Living so close to the Sea allows me to have excellent seeing and good transparency in a lot of nights which become clear. Especially after rain during the day. But without a barlow to bring my numbers down I always fail calibration with PhD2. So simple solution is my 3x barlow gives me a figure of 3.12. Getting closer and believe that my seeing conditions allow good guiding with 3 instead of the magic 2. Have I recently mentioned how much I love your videos?
Hi Cosmicty! The basic difference between a OAG (Off Axis Guider) and typical guide scope is the OAG is mounted on the same focus tube as your main imaging camera. Please see this video: ruclips.net/video/8TClzFbxwhM/видео.html I prefer a Typical Guide Scope, but, if you want to see more about OAG, see this video: ruclips.net/video/yN9WZ7koeks/видео.html Thanks for watching and commenting! Doug
That's great! Would you mind telling me your arcsec/pixel on your setup? arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) I think you could be the exception. Most people that are reporting good guiding at around 2.00 arcsec/pixel. If you're having great success using 50mm Stellarvue, I think this is your formula: 8.24 arcsec/pixel = (206/210) * (8.4) Did you have to do anything special with your autoguiding software to setup this guide scope? Thanks, Doug
It is 8.14 arcsec/pixel. I am no exception. The Lodestar X2 is a superior guide camera because of it's pixel size. I had a ASI120MM before as my first guide camera last fall. Nothing but problems. The 120MM is hit or miss. You can read all sorts of threads if you search for it on Google. It doesn't always play well with PHD2. If you have a good one, which I know a couple people personally that do, you are good to go. Otherwise it has an intermittent connection problem. In my opinion, and I am just under a year into DSO AP, that the X2 gives a higher SNR value. I was getting 40 SNR on a star at best with the 120MM. With the X2 I get anywhere from 150 to 250 SNR. The Stellarvue works great for my SV70T and my 102mm Raptor, but I use an Orion 80mm Short Tube on my ES 152mm CF with the same guide camera. I get Dec problems sometimes, but that is a whole other story. A common problem with mass produced mounts like my CGEM I had and my CGX I have now and it's on a pier not in my observatory. Drives me batty, especially coming out of a dither. I have to jack up the MxDec way up so it recovers faster. I am friends with you on FaceBook too by the way if you ever want to chat further. Douglas J Struble. Future World Media is my company name.
Hi Tolga, Good point, I guess it could, but, When I tried the same mount with 3X barlow, it was spot on. Not sure if you saw in the other comments, but, this formula seems to be the key: arcsec/pixel = (206 / focal length in mm) * (pixel size in microns) In my case I get good guiding when my arcsec/pixel = 1.92, others have reported success closer to 2.00 arcsec/pixel too. If I took that same formula to the 60mm guidescope: Arcsec/pixel 8.04 = (206/215) * (8.4) I was having horrible luck at 8.04 arcsec/pixel. Great guiding at 1.92 Arcsec/Pixel. Just out of curiosity Tolga, what does your AG arcsec/pixel look like using this formula? Doug
8" resolution is pretty low for guiding. Just so I better understand, was the problem you noticed in the star shape or in the guide graph. A tell tell sign of flexture is when the guide graph look great but the stars in the main imager is elongated
In your video, you say that you had the choice of using a long focal length guide scope (listed as F/11.7) or a short focal length guide scope (listed as F/3.6). Those numbers are focal ratios, not focal lengths. The focal length is the focal ratio times the diameter of the lens/mirror. For instance, if your guide scope has a lens diameter of 80mm, and a focal ratio of f5, then the focal length would be 400mm.
I might add that I have used an 80mm f5 guide scope with my 1000mm f5 imaging Newtonian for many years with success. I have also used my club's 142mm f7 Astrophysics refractor as a guide scope for an 80mm f6 Williams optics scope also with success. I agree that if your guide scope has a focal length that is less 50% of the focal length of the imaging scope, then you run into problems with the autoguider making corrections that are too big for the imaging scope. I think that can be corrected somewhat in the set up of your guiding software (such as changing the RA/DEC aggressiveness). But it is better to keep your guide scope at or above the 50% rule. PHD2 asks for information on both the guide scope used and your imaging scope. So it takes the optics of your instruments into account when setting up your guiding session.
I get it! Focal Length is measured in mm and Focal ration is the F speed. Opps! Thanks for the clarification. I also appreciate you explaining more about your 50% rule. Thank you Orgenicman! Doug
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Hi. In general Imaging/guiding should be below or equal to 5 for good and accurate guiding. Long focal length guide scopes are surely more precise and accurate. However mount payload capacity should not be exceeded and this can happen with a heavy guide scope. I have two guide scopes, namely 169 mm and 240 mm focal length scopes and two guide cameras, namely the zwo ASI 120 and 290. Both mini versions. Depending on my main scope/camera combination, I use the appropriate guide scope/camera/Barlow combination to be always below a ratio of 5.
Thanks Jean for your comments!
Doug,
I'm almost certain that the long vs short focal **ratio** is less relevant when compared to the long vs short focal **length**.
From the research I've done, I've found that you want whatever focal length gets you to within twice the pixel scale of your imaging focal length.
For example: If your're imaging at a pixel scale of 1 arcsecond, your guide scope should not exceed two arcseconds per pixel.
With many of the guiding programs we have today, PHD2 being the most commonly used one that I know of, sub-pixel guiding is possible because the centroid of the guide star can be computed to be 'between' pixels. This calculation, along with proper guider calibration, can allow the guiding program to correct for sub-pixel guide star movements.
The 2:1 pixel scale ratio is important because at higher ratios, the sub-pixel adjustments may become too small to correct for errors that may show up in the imaging camera.
I've only ever successfully guided a handful of times myself. And those times that yielded the absolute best results for me were when I was guiding 1:1.
I will be buying a new guide scope for my newest telescope (A 10" Meade LX50) - and even with a 0.63 reducer my pixel scale will be 0.71 arcseconds per pixel using my SBIG ST-8300. Therefore I need to get my guide scope pixel scale as close to 1.5" per pixel as possible.
An Orion ST80 with a 2x barlow lens and the ASI174MM camera will get me to 1.5" pixel scale - and I should be able to benefit from the sub-pixel guiding algorithms from my auto guiding program.
Thanks Mitchell!
I haven't heard this theory yet about 2:1 Pixel scale. Thanks for explaining that to me.
Now, if I use your theory, and compare my "bad" experience to my "good" experience...let's see how it adds up:
Using this formula for arcsec, Victor posted this in the comments earlier:
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
"Good" AG arcsec was 1.92
"Bad" AG arcsec was 8.04
Camera was the same in both tests, the Scope used was an Orion 80EDT using a 0.8 Focal Reducer
480 * 0.8 = 384 Focal Length
5.5 Pixel Size
2.95 = (206/384) * (5.5)
Well in my case that would put
"Good" AG @ 1.92 to Telescope @ 2.95
"Bad" AG @ 8.04 to Telescope @ 2.95
I always have great guiding! So with your theory, please correct me if I misunderstood you...
If my camera is 2.95 and twice that is 5.9, my AG is registering 1.92, it's well below the 5.9.
I can't seem to find a formula that is universal. I have repeated reports of people succeeding when close to 2.0 on the AG, but, I don't know about their main imaging setup.
Very interesting and I appreciate you giving me more info for thought.
Thanks again!
Doug
Doug,
I think you understood and explained it back to me well enough.
I do think that the reason you cannot find a universal formula is because everyone guides differently.
Two people with identical optical tubes, guide scopes and cameras may use two different programs that calculate the centroids of the guide star differently. This will result in different guiding.
The same two people may agree to use the same software the next night, but one telescope is not properly balanced. Again this will result in different guiding.
In doing a little more research on this topic after your video, I stumbled upon this website, which has a very interesting calculator that seems to support your "Bad" AG setup as likely being a good guider...
Check it out, play around with it. It goes completely against my 2:1 rule of thumb - but I'm always open to try new things when presented with compelling evidence. I may try this out as well with my 10" some day.
www.wilmslowastro.com/tips/autoguiding.htm
Wow, that's really interesting. No one can agree on a "perfect" setup. In my case, I just grabbed a barlow, and it worked better. So while it "may" work better for me, it may not work better for other people.
Of course, if it's working, leave well enough alone! I thought I'd throw out my finding to other people and see if anyone else could/would benefit from results.
I never thought AG would be so complicated! I've been lucky and I can AG 30 minutes subs no problem when I want. And that's with an Atlas Mount. I also use 2 second exposures in my AG routine.
Thanks Mitchell for bringing up more possibilities in this discussion, I appreciate your feedback.
Doug
sharing our ideas is what grows the hobby. Glad I could do my part!
Clear skies, and I look forward to your next installment :)
Interesting question, have you changed the settings in the guiding software before you used the shorter guidescope? I used a 53mm aperture guidescope at f 3.6 at 190mm and tested up to 10 min exposures imaging with Skywatcher ed80/600 with good guiding 0.5 to 1 arcsec/pixel, using Zwo 120MM-s monochrome camera, and having an image scale of 4 arcsec/pixel. I recently tested with success imaging 4 minutes using a Ritchey Chretien 6 inch telescope 152/1370mm, at 1370 mm focal. Have to research more on this subject, but I think longer focal length for the guidescope is more critical when you use longer focal lengths with your imaging scope, maybe from 1500 higher, a good compromise between focal length and focal ratio might be needed so you have not only a better image scale arcsec/pixel, but also a good signal to noise ratio
Hi GAM, No I didn't change the software settings. Other people have made the same comments. My mistake. I do enjoy the longer focal lengths. I have taken in the past 30 minute exposures with no problems. My refractors do not have long focal lengths. Thanks for commenting and sharing your advice. Doug
@@Myastroimages with pleasure. I comented also on a video of yours some time ago you had the wrong setting for the youtube kids and advice to change to the one that is not for kids so you get monetized and not having other problems because of the wrong settings. My channel is smaller i have started to grow my channel one year ago but growing was not so fast but hope will be better.
@@GalaxyArtMedia I originally started my channel for me. Helped me keep track of things I learned. Your channel will grow. I'll sub to you! Thanks!
@@Myastroimages Thank you very much Doug! I am glad you did! Ioan (John).
I like your idea of putting a Barlow on the guide scope. I happen to have a 2.5x laying around, going to try that out!
It's worth a try! Good luck! Hope it works for you!
@@Myastroimages I think it will for my new EdgeHD 8". I'm putting a WO 50mm (200mm FL) for guiding, and I think a Barlow will put it in the perfect ratio of "within 1 to 5 ratio". 2000 / 400 = 5/1
@@ryanmichaelhaley 200MM / 50mm = F4 Native
EdgeHD 8" 2032mm / 203 = F10 Native
If you use a 2.5X Barlow, that would make your guidescope F10
Much closer match to your scope's native F10
Hopefully when you try it, you'll see a noticeable improvement!
@@Myastroimages I hope so, and I heard that you want the focal length of the guide scope to be at least 1/5th that of the primary scope. As long as the Barlow puts the guide scope past 400mm, then it's perfect for the 2000mm EdgeHD 8.
Makes perfect sense. As with most things astrophotography-wise its all about the 'F' factor. Fantastic and to the point.
Thanks for watching!
There is nothing wrong with either setup. Your issues more than likely had to do with reconfiguring your guiding software with the correct focal length settings of the new scope. That being said, guiding with a scope that complements what you are imaging with will help. If you are imaging with at 2000mm+, a longer focal length might perform better.
Thanks for the feedback!
Thank you for showing this. I am learning from all this teaching. Excellent program.
Glad you found this useful. Thank you for commenting!
I am using ZWO 60/280mm guide scope with ASI120MC. No problem in guiding my wide field imaging scope. :)
Good to know. It could be my particular guide camera. I've seen other people commenting on their results too.
Tommy Lim KW I use the exact same setup, but I noticed that if I go over around 4mins my stars start to drift. I'll probably give a go to the barlow.
My main imaging scope is only 100/400 F/4 astrograph. So, I believe barlow is not needed in my case. How about yours?
Tommy, I know you're asking Peter, but, for reference, my imaging scope is 80mm running F/4.8 (Using a reducer).
Tommy Lim KW Mine is 200/800 astrograph. Also f/4.
No guiding prob here ... but, in my travels I've read that guiding software often doesn't play nicely with sharply focused stars. There can be too steep a 'cliff' in dropoff of brightness at the edges of a sharp pinpoint star. So if using finderguider / short focal length / wide field of view / low mag guidescopes, it can help guiding by defocusing a bit .... gives the guide software more pixels 'width' for the star for it to find the centroid of.
Like I said, I don't have problems 'falling' off the guide star, but I have read the above comment a few times now (when I've been searching for info on how to read and use the DEC/RA charts in the guide software and how to use that to adjust all the other many options in the programs!).
Congrats to you for the out-of-the-box solution though! Throw a barlow in, thus avoiding having to spend $ on longer FL guidescope, dovetail, rings, etc which then may flex more, weighs more on your mount, maybe even forcing a mount upgrade(!), etc. So great vid. Thanks for posting that up.
HI Carl,
Yes, I've heard of soft focus ag stars too. I don't do a fine focus on my AG. Thanks for sharing your AG details and I appreciate the comments and thumbs up!
Doug
I wondered about the barlow... I have a 2x barlow I never use, and as yet havent tried with my guide scope.
Will give it ago.... when it stops raining :)
Give it a try if you're having guiding issues. Hope it works well for you! Good Luck!
Scope is best used at its native FOV , cant be bigger , can be smaller but if you decrease FOV to get more magnification then you lose aperture for you are wasting the rest of it and that means lower resolution ,so for guiding you can use Barlow to get that F ratio up to F10 , but for imaging , if you move it down goes you quality . Its the way she rolls
Thanks for commenting.
Thanks for sharing Doug, this opens my setup to a whole lot more other options :)
Thank you for watching!
Hi, I struggle to guide with my 50/183 guide scope. I am really leaning to its short focal length to be the culprit. I'll try inserting a barlow. Thanks!
Good luck! I hope this helps.
Hi Doug
I have an Orion 110mm f6 & use the 60mm guidescope
I have had good results using phd & my canon dslr
I have only started in this field but am happy with results so far
I really enjoy your videos
Looks like your viewing area is fantastic
I'm in very urban environment in Sydney area in Australia
Keep up great work
Cheers
Thanks Rider! I appreciate your comments and views. You know, one of the best things to do...is to leave well enough alone! If you Autoguiding is working, then that's great! Just keep it in mind. I was surprised when I found a barlow helped my AG performance.
When I travel to my darksite, The skies are good, but, it's a struggle to find dark skies as you know. Sydney must be challenging for LP. You should try traveling to a dark site if possible. It's worth the extra effort.
Doug
Thank you...good job thats the kind of stuff I need to know..I'm just starting...but a quick learner and this very issue was a concern...I'm in Subscribed
Thanks Maximus. There are differing opinions out there as you know. Even in the comments here some people were suggesting no problems with a F/3.6 guide scope and suggested I try adjustments in the imaging software. Good luck on your new adventure! AP is very rewarding.
Doug
Due to bad situations in life, I am not currently able to get out and do any kind of astronomy work. In fact, I'm going to have to replace much of my stuff at some time in the future. So, I can't test this, but I have to wonder, what are you using as your guide software, and is it properly configured for your guide scope?
More specifically, are you using something like PHD2 and did you set up the focal length correctly in the software for the scope?
I realize this was two years ago, but I'm now curious as to how that works for you.
Hi Gary,
Yes, other people have mentioned here too about software settings. It was very easy for me to try both long and short focal lengths. I'm probably imagining this, but, wouldn't you think a more narrow view would be more precise than a wider view? Anyway, I know it works for me. Each person often finds the best option for themselves. I hope your situation in life hasn't deterred you from trying. You'll have to be creative and I'm sure you're very creative if you've tried this hobby. Good luck!
Doug
@@Myastroimages Doug, from the gurus over on Cloudy Nights, it's more about image scale and the camera you're using. Honestly, I don't understand any more. I had an Orion SSAG setup, and that worked pretty well (considering I have A Celestron AVX).
i've been using a 60mm, 240mm focal length, f/4 guidescope successfully through PHD2 for a few months now using a zwo asi120mc and guiding camera. Did you create a new guidescope profile on PHD2 (or whichever guiding software you're using) for the 60mm? I wonder if you may have kept the the same profile and when the specs of the 60mm/barlow combination got close to the larger guidescope specs your guiding software began working as before.
Hi NoNo,
No I didn't create a profile. I use MDL. But, I've never created a profile before for AG. It would probably help. Thanks for the suggestion!
Doug
Thanks for this video and the informative comments discussion. I have been having issues with my Orion 60mm F4 guide scope so will give it the Barlow treatment next time out. I have been using the newer LPI-gc camera and PHd2.
Let me know if it works for you! The comments from other people have been great. Victor explained a formula and it seems to work.
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
It would be an interesting comparison if it works for you. While there isn't a perfect Arcsec/pixel size for AG, it seems 2.0 is the magic number. Mine before was 8.04 and after 1.92 arcsec/pixel. The 1.92 worked well for me.
Doug
Oh man have I had problems with the shorties. I have the Orion guide scope and it is just horrible. I constantly lose stars and PHD is always jumping around when I check back. Adding a barlow is a neat idea. Good thinking!
Yes, that was happening to me too, losing stars, and bad tracking. With the Barlow I noticed an improvement. If you're having the same problem, get any old cheap barlow, and give it try. I think you'll be satisfied with the results!
Did you need to use an extension to get your 2x barlow to reach focus? I use the Orion 50mm with the Orion SSAG giving me about 6 arcsec/px. Haven't tried my 2x barlow yet. Waiting for clear skies. Thanks for the info!!!
Hi Jeff,
No, I didn't need an extension. I hope this works for you. It sure helped me.
Doug
its a good job i watched this guide scope is on my list its just after the Crawford focuser i need first for my ar90mm x900mm bresser scope the one i got with it was mediocre at best it's worshiped and prayed to every night :) good tip i was going to get that exact one 60mm in a few weeks time
I hope this helps you achieve good autoguiding. Thanks for watching!
Net ty hello do u have exos2 goto mount?
I use a 60mm guidescope on my 9.25 SCT, F4 Astrograph and even on my Canon 300mm f/2.8 wide field setup (which I typically stop down to f/3.5). I've had good results with all of them. My main issue is differential flexure on my SCT. Already have plans for moving to OAG on it soon.
Doug, you didn't really specify what "problems" you're having. When you say problems, are you talking about your guiding error? Weird star shapes?
My bad, you're right, I should have explained my "problems". What was happening is I was losing tracking. It would ride along for a while ok, then I think wind or atmospheric turbulence would cause it grab another star. So the best way to describe the "problem" is not holding a single star to track with.
Reading some of the other comments, there is a formula that seems to work. In this short review, it seems Arcsec/Pixel close to 2.00 works best. When I have good tracking on the long focal length scope, I had 1.92 arcsec/pixel. Another person reported good auto guiding at 2.07.
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
It would be interesting to hear what your Arcsec/Pixel results are for your AG.
Hi Doug, this could explain the formula a bit: The guide software will only send a correction pulse to your mount when it detects movement of the guide star. To calculate an accurate star position, the light from your guide star needs to be spread across multiple pixels on your guide camera sensor. When the guide scope's focal length is too short, all the light from the star will fall within a single pixel and it will only move to the next pixel after a large tracking error, so your guiding will be bad. The formula is useful for comparing the difference in image scale between the guide camera and imaging camera (see the other comments).
Excellent Victor! Thank you!
For my experience, some guide problems are correlated to seeing condition and short focal lenght is better than longer...
If the mount have not big meccanical problem and is good polar aligned, the seeing are the big problem...
The guide star "dance" in the guide ccd and the mount are not able to guide too many correction guide pulse...
I take photo with RC 1500mm focal lenght and guide with 700mm with binning 2 ccd guide (same effect of 350mm guide lenght)
Thank you Michele for contributing to the discussion.
Doug
I have a very good quality 80mm fl 7.5 refractor for imaging that I will use as a guide scope for my 100mm refractor...no problems....maybe because it's pulling in brighter star images? I do remember an equation that looks at several parameters to suggest a proper Gide scope for any given imaging scope....as I recall one of those parameters was focal length ....
Thanks Human! I'll bet there is a setting. Seems like there are so many settings under settings that are nested settings, sometimes they're hard to find.
All the best!
Doug
I think there is a formula for optimal guide scope fl and speed based on your imaging scope and camera. intuitively it helps with higher mag if you have good seeing and remember fewer stars to pick from. Otherwise there's other things you can do with binning and such. I think the idea is get it close to optimal without a lot of moving parts for flexure.
I've never seen this formula, but, I'll bet you're right. I've never tried binning. I just found this interesting when I saw the results. Took what I had and gave it a try. I like the longer focal lengths!
I'll try to find it. A fellow told me at one of the recent star parties cause he saw my set up. I know Adam and Co at the Astro Imaging Channel might have covered it. BTW I watched ALL your how to videos. Helped me over the years. Marty
Victor commented below about the formula:
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
When I calculated my setup I was 1.92 Arcsec/Pixel and Victor was 2.07. So I'm guessing anything close to 2.0 is good.
I appreciate the loyal views and comments Marty!
Doug
Hi Doug
As the old saying goes " if it ain't broken, don't fix it! "
Yes I agree with viewing at dark site.
I'm hoping to image with dslr in US this coming September, as I'm taking family on holiday to US
We will be traveling thought California, Oregon,Washington & then through Utah & Arizona
I have been researching dark site so I can use dslr for nightscapes.
Keep up the great work
Cheers
Thank you! Enjoy your holiday!
Which guide camera are you using Doug?
I'm using a 50/205 mm guidescope with an ASI120MM camera (3.75um pixels) to guide my 80 mm f/4.8 refractor. That's a resolution of 3.77 arcsec/pixel for guiding, while the main camera (ASI1600MM-C) operates at 2.07 arcsec/pixel. If you're using something like a Lodestar X2, which has much larger pixels, you will need a longer FL guidescope.
Here's the formula for calculating your pixel scale: arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
Hi Victor,
I have an older Lodestar AG camera. The specs are "CCD Full resolution Pixel data: Pixel size: 8.2uM x 8.4uM, Image format: 752 x 580 pixels" So, using your formula, BTW, thanks for formula. 1.92 Arcsec Pixel = (206/900mm) * (8.4) , So that matches closely to your 2.07.
I guess you're saying the best results are when your Arcsec/Pixel are close to 2.00 +/- ?
Thanks for explaining it! All I knew is that it didn't work with the shorter focal length. Since my Lodestar has a larger pixel size, that explained why it was happening!
Doug
Modern guide software such as PhD2 can calculate the guide star centroid with sub-pixel precision. So the image scale from your guide camera can be larger than the image scale of your main camera, up to 3-4 times. In my setup, the difference is 3.77/2.07 = 1.8 so that's well matched.
Thanks Victor for all your help! Many other people have commented about poor guiding and it looks like it's due to the wrong Arcsec/Pixel size. The formula you provided is very useful to understand where you're at now and where you should be.
Software may be able to accommodate for other configurations like you pointed out, but, many people do not know or understand how to use the software.
I had no idea about this formula, all I did was start grabbing parts, and it worked with a barlow! But now with your formula, it will back up my findings.
I think this deserves a follow up video to explain your formula. Thanks again!
Doug
That’s probably why OAG’s are popular for longer focal length scopes. You just can’t guide accurately when you ratios of scopes is far off.
True Nathan. I find the OAGs are a little more difficult and I like easy. Who knows, maybe one day I'll take an OAG. Thanks for the comment and watching.
Doug
check ur FL in PHD if ur using it... that makes a big diff.. if u have a 162fl and ur phd is set to 300mm.. mmm guess what.. tho.. i might try a 2x barlow to see if it helps for myself setup... any little thing that gives a few secs more of good guide is worth a go ..
Yes, it's worth a try if you have a 2X barlow laying around or if you're having guiding problems. Thanks for the FL tip!
I have used a barlow on my Skywatcher Startravel 80 guidescope to use with a Synguider. Guiding software like PHD have the ability for subpixel guiding, but the Synguider lacked this ability, therefor I had to use a barlow with my guidescope.
Good to know. The more I'm reading comments here, there seems to be a formula, but, I haven't found the ideal calculations yet. All I know, just like you found, a barlow helped. Thanks for commenting your solution!
Hey matey, let me trump everyone and tell you that I've been guiding (5 - 8m subs) using the humble 30mm guidescope which has a FL of only 130mm with my SCT reduced from 2032mm to 1422mm FL without any issues :) mind you, I'm using the smaller chip for my guider which is the QHY5L-II mono camera
Hi Ahmed,
Interesting! Would you mind telling me your Arcsec/Pixel size?
Further discussion has uncovered this formula for your Autoguiding Setup:
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
People so far that have had good success guiding have reported approx 2.00 Arcsec/Pixel. Since you've have great success, I wanted to see how you compared using this formula.
Thank you!
Doug
would a celestron travel 70 be a great starting guide scope and suggestions would be helpful
I used to have this scope and seem to recall the crayford being made of plastic. Unusable.
Did you actually calculate what would be needed for good guided main images and your telescope? It has to be in a certain range for it to work with the main scope and depends on focal length, sensor pixel size etc. I use the calculations to choose my next guider and/or guidescope.
Hi Vincent,
Victor commented on a formula. arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
When I take that formula and apply it to my scope, my arcsec/pixel = 1.92. I don't know the ideal range, but, Victor says his was 2.07 on his rig and mine was 1.92...so I'm guessing the the correct range is close 2.00 arcsec/pixel.
Do you have any suggestions for the ideal Arcsec/Pixel for Auto guiding?
Doug
Astrophotography Tutorials Indeed! So you can calculate that for both guide- and main scope, then the value of the guide scope should be lower than 4x the number of the main scope (edited and corrected)
Hey Doug! Thanks for the many great videos. I have saved a lot of time and money thanks to them.
Where im at in astrophotography is, that i think I should ditch my typical guide scope, and use a off axis guider. ( In my head) that would eliminate all flexure and I could find a guide star in my wide field of view. But..... THE INTERNETS, says I should use an oag with a long focal length scope. like a sct.
Am I missing something?
Hi John,
I'm glad you've learned a trick or two to save some money. There is no rule about anything in AP. Many times it's people who try new things that discover better ways. The OAG isn't for the faint of heart. There is a lot of tweaking needed to make it work, plus, an OAG gives you a very tiny area to pick up stars. If you do decide to look at OAG, Chris Gomez did a video for me a while ago explaining how to set one up. ruclips.net/video/yN9WZ7koeks/видео.html It's worth taking a look at, especially the helical-focuser.
I appreciate hearing your comments about the videos, it makes it worth the extra time and effort.
Doug
Now when there's multistar guiding - I don't think a long focal length guidescope would be a good choice. Too few stars in the fov to guide with.
I learned something new! Thank you Maciej for letting me know about Multi-star guiding. I've never tried that before. What software do you use for Multi-star guiding? Do you see better results using Multi-Star Guiding?
Welcome back Hubble
Thank you XDerDerx! Glad to see you here! I appreciate the comment.
Doug
lol...love the music at the end!
Thanks for watching! :)
With my 9x50mm guidescope I have never succeeded with guiding and always received the message " star did not move enough" when calibrating with PhD2. Best idea is either an 80mm telescope or as you have found a 3x barlow.
Hi Peter,
Yes, after reading more of people's comments in this thread, there are mix results...Some people have no need for a barlow and some people do require a barlow. Apparently there is a formula. arcsec/pixel = (206 / focal length in mm) * (pixel size in microns). Getting close to 2.00 arcsec/pixel seems to the magic number. Mine was 1.92 and another had 2.07 with reported good results!
All I did was try what I had on hand and without the formula, I found a 3X barlow worked best. But, using this formula would probably work too!
Doug
That means with my guider as the formula puts my setup as 9.38 without any barlow so is this too much which I guess is because it means I have 9.83 arcsec/pixel. Wow.... I use a lodestar with 8.2 microns per pixel. Trust me to expect too much of PhD2.......
Let me know What happens Peter! I think once you get your arcsec/pixel closer to 2.0 you'll see an improvement. The formula is very helpful, but, I haven't seen the "good Number" to hit. Right now, I'm guessing 2.0 is the magic number, but, If can confirm, that would be 3 people with good guiding at 2.0.
Thanks Peter!
Doug
Living so close to the Sea allows me to have excellent seeing and good transparency in a lot of nights which become clear. Especially after rain during the day. But without a barlow to bring my numbers down I always fail calibration with PhD2. So simple solution is my 3x barlow gives me a figure of 3.12. Getting closer and believe that my seeing conditions allow good guiding with 3 instead of the magic 2. Have I recently mentioned how much I love your videos?
Thank you Peter! I appreciate your comments and your views. Have you tried the 3X barlow yet? I'm really curious in your findings.
Doug
Did you change you focal length in phd2 settings when you switched guide scopes?
No, I was using MaximDL. I haven't used PHD in long time, but, PHD is a very good software.
Should be a focal length setting no matter what program you are using and if you didnt update that it would cause your problem.
Good to know! Thanks Antman!
Hope it helps. If it does let us know. Here is the link. Calibrating the Guider diffractionlimited.com/help/maximdl/HIDD_GUIDE.htm
Hi Doug,can you please help me understand properly , what is the difference between a Typical guide scope & an off Axis Guider . Thanks Doug
Hi Cosmicty!
The basic difference between a OAG (Off Axis Guider) and typical guide scope is the OAG is mounted on the same focus tube as your main imaging camera.
Please see this video:
ruclips.net/video/8TClzFbxwhM/видео.html
I prefer a Typical Guide Scope, but, if you want to see more about OAG, see this video:
ruclips.net/video/yN9WZ7koeks/видео.html
Thanks for watching and commenting!
Doug
Thanks Doug
Thanks for info, DougDog
= )
DugDog was an old Game Name I used to use.
Sorry Doug,got mixed up mate !
Thanks Doug for this video. Duh...barlow. why didn't I think of that!
Thanks Goose!
Weird. I use a 50mm Stellarvue for my 102mm and seems to work just fine. I'm using a Lodestar X2, though. I would never use another guide camera.
That's great! Would you mind telling me your arcsec/pixel on your setup?
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
I think you could be the exception. Most people that are reporting good guiding at around 2.00 arcsec/pixel.
If you're having great success using 50mm Stellarvue, I think this is your formula:
8.24 arcsec/pixel = (206/210) * (8.4)
Did you have to do anything special with your autoguiding software to setup this guide scope?
Thanks,
Doug
It is 8.14 arcsec/pixel. I am no exception. The Lodestar X2 is a superior guide camera because of it's pixel size. I had a ASI120MM before as my first guide camera last fall. Nothing but problems. The 120MM is hit or miss. You can read all sorts of threads if you search for it on Google. It doesn't always play well with PHD2. If you have a good one, which I know a couple people personally that do, you are good to go. Otherwise it has an intermittent connection problem.
In my opinion, and I am just under a year into DSO AP, that the X2 gives a higher SNR value. I was getting 40 SNR on a star at best with the 120MM. With the X2 I get anywhere from 150 to 250 SNR. The Stellarvue works great for my SV70T and my 102mm Raptor, but I use an Orion 80mm Short Tube on my ES 152mm CF with the same guide camera.
I get Dec problems sometimes, but that is a whole other story. A common problem with mass produced mounts like my CGEM I had and my CGX I have now and it's on a pier not in my observatory. Drives me batty, especially coming out of a dither. I have to jack up the MxDec way up so it recovers faster.
I am friends with you on FaceBook too by the way if you ever want to chat further. Douglas J Struble. Future World Media is my company name.
Thanks Douglas! I have the older Lodestar, not the X2, but, you're right about the Lodestar being a great AG camera.
Doug
Hi Doug, could it be because of the way two guide scopes are mounted?
Hi Tolga,
Good point, I guess it could, but, When I tried the same mount with 3X barlow, it was spot on. Not sure if you saw in the other comments, but, this formula seems to be the key:
arcsec/pixel = (206 / focal length in mm) * (pixel size in microns)
In my case I get good guiding when my arcsec/pixel = 1.92, others have reported success closer to 2.00 arcsec/pixel too.
If I took that same formula to the 60mm guidescope:
Arcsec/pixel 8.04 = (206/215) * (8.4)
I was having horrible luck at 8.04 arcsec/pixel.
Great guiding at 1.92 Arcsec/Pixel.
Just out of curiosity Tolga, what does your AG arcsec/pixel look like using this formula?
Doug
Astrophotography Tutorials Hi Doug, I use a QSI camera with built-in guide port and my guider image scale is 4"/pixel vs main imager 1.68"/pixel
Thanks Tolga!
8" resolution is pretty low for guiding. Just so I better understand, was the problem you noticed in the star shape or in the guide graph. A tell tell sign of flexture is when the guide graph look great but the stars in the main imager is elongated
The problem was simply losing tracking. It would bounce off one star, grab another, and bounce again.
You are confusing focal length with focal ratio.
Could you explain in more detail the differences? I'm always eager to learn.
Thank you!
Doug
In your video, you say that you had the choice of using a long focal length guide scope (listed as F/11.7) or a short focal length guide scope (listed as F/3.6). Those numbers are focal ratios, not focal lengths. The focal length is the focal ratio times the diameter of the lens/mirror. For instance, if your guide scope has a lens diameter of 80mm, and a focal ratio of f5, then the focal length would be 400mm.
I might add that I have used an 80mm f5 guide scope with my 1000mm f5 imaging Newtonian for many years with success. I have also used my club's 142mm f7 Astrophysics refractor as a guide scope for an 80mm f6 Williams optics scope also with success. I agree that if your guide scope has a focal length that is less 50% of the focal length of the imaging scope, then you run into problems with the autoguider making corrections that are too big for the imaging scope. I think that can be corrected somewhat in the set up of your guiding software (such as changing the RA/DEC aggressiveness). But it is better to keep your guide scope at or above the 50% rule. PHD2 asks for information on both the guide scope used and your imaging scope. So it takes the optics of your instruments into account when setting up your guiding session.
I get it! Focal Length is measured in mm and Focal ration is the F speed. Opps! Thanks for the clarification. I also appreciate you explaining more about your 50% rule.
Thank you Orgenicman!
Doug
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