Thanks for your work and sharing the process and results. Great resource as I recently installed the Celestron V2 focuser on the new C9.25 Edge as my first foray into the autofocus world (after I found out just how touchy that manual focus is even with the Celestron Reducer installed). My initial runs were absolutely terrible and then I followed your video and was soon getting similar results with a very nice parabolic curve on both sides. I found that 150 for the out backlash setting really did the trick as you suggested, and for my setup, a step size of 50 worked great.
Great! I’m glad you got it working. Nothing more frustrating than to have everything set up and then can’t get good focus. I didn’t know Celestron had a newer version of their focuser. I’ll have to look that up.
Very good and explanatory video my friend. Very useful for SCT users. Keep giving out your expertise. That's what makes this hobby interesting. Solving problems and getting better!!!
Hi James, nice video. I have been using Hocus Focus on my C11w0.67 reducer for about a month now with great results. For what it’s worth, I didn’t have to change any of the more advanced settings to get it working well. On the main plug-in configuration page for HF, there’s a setting for “Long FL” and “wide range” for the focus range that’s giving me excellent results. The HF developer even recently added some updates for SCT star detection for accurate HFR measurements even when significantly out of focus (donut stars).
Great feedback, Matt! That’s good to hear…the parameter list looks like a project for a full Moon. It’s nice to hear that there’s a “long focal length” preset. I’m looking forward to digging into it and giving it a trial. Thanks for watching!
Absolutely agree with your comments regarding the Celestron Focus Motor. It's been good for simple focus purposes but I've experienced the same overshoot in backlash and need to over-compensate the values for better autofocus routines. Great video! Thank you
I just watched your Antlia filter vid. I'm about to buy a set. I laughed when you mentioned the huge halo around Alnitak with the ZWO OIII filter. I know it well. Like any good astrophotographer...I blame the equipment for my less-than-expected results! I'll drop a note on your channel...
Hi James, bit of an older video but still relevant today. I’ve been experiencing a lot of what you’ve covered here. I have a very high precision electronic focuser, on the order of 7nm steps. I’ve just recently fitted it to an EdgeHD 8 and my step size and overshoot numbers have been very high with HFR being very inconsistent. I’m looking forward to working with some of the additional settings you’ve outlined here. Cheers! Doug
Looking good Jay! Btw, since your last video on this topic, I have been testing Hocus Focus and it operates very well, in fact I am changing it to my primary focusing method. The part I like about it is that it detects all the stars in the image thus you get better averaging of the HFR. Also, because it detects all the stars, using the abberation inspector in NINA helps me adjust for tilt better as now I can see more annotated stats within the ab inspector image; So good job for the creator! The only thing I would hope the creator would do is to allow single star auto focusing. I have been testing a lot of lucky style imaging techniques at focal lengths up to 14,000mm and I really need a single star focusing method. One thing I don't like about Hocus Focus is there seems to be a bug with turning on and off annotation from the image view, some times it doesn't turn on or off so I have to go to their setting tab thus adds another step. Keep it up buddy!
The curves look much better now. Great to hear about your experience with Hocus Focus! I’ll probably make that switch myself once I get done with a couple of targets with SCT. Then I’ll reconfigure and add the focal reducer and start 2x2 binning. At that point, I’ll dial in the settings for Hocus Focus. I hope you mean you’re imaging at 1400 mm! Haha. I think the Hocus Focus algorithm is being actively developed and the SCT focal range is the last to get any love. I’m optimistic about though.
Thanks, Ernie! I'll wait to tackle the Hocus Focus settings after I reconfigure my SCT with the focal reducer and 2x2 binning. I have to finish up M1 and M81 in the current config (no FR and 1x1 bin) before I switch. There's a ton of fiddly-looking parameters in Hocus Focus right now. I hope that as experience with it grows, the plugin can "tune" itself for a given imaging setup. We shall see.
Thank you for the video. It gave me some great ideas. I have an edgehd 14 with no reducer, and perhaps unsurprisingly the narrow band filters are a problem. I can double bin, but if I triple bin my uncertainty gets huge.
@@matthewbrown8679 Uggh. A C14 is a challenge. A set of par focal filters is a blessing. If you can focus with the Lum filter and simply switch to Ha, O3, and S2 that eliminates a lot of heartache. Good luck!
Excellent topic and great video as always James. I bought the Celestron motorized focuser when it first came out. For the most part, it works fine but every so often it glitches and my curve looks awful. You've provided a few great tips and I might look to the Pegasus or ZWO in the future. Clear Skies!
Glad you're having a (mostly) trouble-free experience with Celestron's focuser. Very frustrating when equipment issues put a stop to an otherwise good night for imaging. Arghh. Thanks for watching, David!
I use the EAF on my circa 1983 Celestron C8. As I commented in your earlier video, I set the backlash value *way* high, some 3-4x the actual backlash value. I set is such to be always "pushing in" on the mirror. That extra mirror movement, at least for me, eliminates the wonky focus off-curve steps that I sometimes got similar to what you showed.
Yep. That seems to do the trick for me as well. Could be that in vs out is a smaller factor than the magnitude of overshoot move. Hey, when it starts working, I stop asking questions. Thanks for watching, Bruce!
@@BruceMallett Makes sense. Seems straight forward enough now. Really appreciate the info. Your after saving me quite a few hours. I’d be going down that “Rabbit hole” as James would put it, been down there enough 😁
Hi James. Thanks for a great Vid. One question: you set your AF step size to 20. Isn't that way too low for a SCT. My C9.25 and my RASA8 require a lot of focuser movement to get the focus to budge, a design feature of SCTs. Wouldn't that create a very shallow curve if it worked at all? But apparently it works for you, so what am I missing? Thanks - Tommy
Well, the step size depends on the mechanical focuser in the SCT and the gears in the focus motor. I'm using the Celestron Focus Motor (I'm not a big fan) which is much more coarse than, say, a ZWO EAF or a Pegasus Astro FocusCube. So it takes fewer steps with the Celestron focuser to sweep through a range of HFR values (I try to limit the range to 3 times the optimum HFR). If you're using a different electronic focuser, then your number of steps may be different. Experiment, Experiment, Experiment! Thanks for watching, Thomas!
Another really interesting video. I’ll be looking into some of those parameters to adjust for my 10” Meade SCT. I used to have a fairly crappy Crayford focuser and was not getting great results and in the end forked out for the Primalucelab Esatto 2” focuser so now i lock the primary mirror and let the Esatto do it’s thing and it seems to be producing nice consistent curves. I just had to get my head around using a step size of 6000 steps with this focuser :)
That's the way to go, Logan! I wish I had one of those after all of the other issues I've had with the Celestron focuser. Haha, I think 6000 steps would have me scratching my head too. Must have VERY fine steps. Clear skies!
great video. I have heard that using a combo of hyperbolic + Trends is a good option, any thoughts on that? I recently got a Moonlite focuser/rotator and I'm wondering if the backlash needs to be adjusted to a lower value now...(I have a Esprit 120 refractor), guess I need to do trial and error testing.
Hey Greg. My view is that an ideal data set (HFR vs focuser pos) “looks” like a hyperbola. If you go waaay out of focus (assuming the HFR estimation algorithm still works), the hyperbola approaches linear asymptotes that look like the crossing trend lines. But you have to go waaay beyond focus and probably should throw out the data near optimum focus. In summary, I don’t like dual fit approach (please note that me not liking it doesn’t mean it’s bad!). I try to keep my autofocus runs in the range where the hyperbolic curve applies and, hence, never go so far out of focus that I capture the asymptotes. I stick with the hyperbolic fit and try to generate the bast noise-free HFR/position data set that I can. Congratulations on the Moonlite focuser! I don’t have one, but sounds like they make awesome stuff. So, yeah, probably want to revisit the backlash setting. Then again, if you get good performance, there no need to change anything. Thanks for watching!
Your apparent knowledge of these complex auto-focus parameters is academic. It's hard to image where all this know-how came from! I have to just follow along and hope it gradually sinks in across multiple viewings. I have the difficult and challenging RASA 8, does it count as a SCT? And of course, no EFW and no focal reducers and no binning. My tilt is nothing short of terrible, in fact "extreme" as noted by ASTAP numerous times. I have ZWO 2600s, the MC and MM. Both show the same tilt depictions and in both of them, the tilt moves with the camera rotation of 180 degrees. I also have the ZWO EAF, so I am now switching from the ASIAIR Pro to NINA in order to get some help and use Hocus Focus. Of course my corner stars are out of focus donuts, but they are also pulled into eggs. Not pretty at all. I tried 2 different camera adapters, both said to produce ideal back focus, but neither improved the corner stars. I am trying thin shims to try back and forth to find a back focus that the rig likes, since it doesn't care about "ideal". And I will investigate collimation, though I don't believe my scope is SO far off to be producing the results i get. I hope that your videos and Hocus Focus will give me at least some clue as to where this bad tilt is coming from. You indicated that it is really for refractors, which I would think are less tilt prone to start with. Many are using Hocus Focus with the hyper-expensive "Octopi" in order to basically adjust out the tilt, regardless of where it's coming from. Problem being, that's for ONE camera only, and I have two. I don't think its right to simply give up LRGB imaging for the octopi. Thanks for your amazing expertise, ha, I will send you my RASA!!
Hey Paul, As you know, I don't have a RASA. If it's not a form of SCT, it's awfully close. Of course, the RASA is used like an SCT with a Hyperstar system (imaging at the secondary mirror location). But, I gather, you do focus by moving the primary mirror (right?), so some of those same challenges. Most comments about the RASA I hear are very positive. How are you able to rotate your camera? Rotator? I've seen a few people use Hocus Focus tilt measurement to guide their tuning efforts (seems very useful). But of course, you've got to have a tilt-adjustment capability. I have not used that feature of Hocus Focus (yet). Have you looked at other tilt adjustment components? The Octopi looks pretty expensive. Sorry I'm not any help here. You're in uncharted territory for me. Good luck!
@@Aero19612 Yes, the RASA is great and fast. But, it has a tiny range of back focus which is critical and hard to get right. And perhaps my ASI2600s aren't a good match for it. I tried to ignore my corners and crop them out, I had to learn other stuff. But when I got slightly proficient, the bad stars couldn't be ignored. I'm trying to learn NINA to help with this problem. I'm not sure my problems are fixable regardless of what I do. Camera rotation is a total pain on the RASA. Remove dew shield, reach in there to twist camera when it's got 3 wires attached. Dont push or pull! Don't unscrew the camera and mess up the back focus! It can be done, but not easily. Ha, you have to be desperate. My problems aside, I wish to read more about your knowledge of star quality. Wish I knew that stuff!
Great work - I'm going to start saving focus runs (with Hocus Focus) so the next morning I can view the actual focus images and maybe learn more about why some of them are 'bad'. At 2000mm (my SCT) I assume some of it is just an ill-timed gust of wind or cable tug - or even seeing
Yes. That's a great feature that Hocus Focus offers. Do you look at the stored autofocus curves like I show in the video? Those can also provide some insight.
I have the optec fastfocus secondary mirror focuser - this issue will remain. It's not mirror flop for me either and I really don't think it's backlash. Gotta be donut + optical artifacts specific to the optical design that throws the algs off. What happens to the donut near or after focus, particularly if you can't get all stars on the massive imaging region in focus at the same time... maybe after it crosses critical values the donut/inverted donut artifact throws off the hfr/fwhm analysis.
Hi Jason. SCT focusing is a challenge, for sure. Some SCTs more than others. One of the problems, is that the mechanism that moves the primary mirror has to have some free play and can't be observed because it's concealed in the tube. Your secondary mirror focuser should get around that (one would think). Do you have primary mirror locks on your SCT? For me, I guess I'm lucky, cranking up the backlash number really helped to sort things out and I got good focus results from then on. In an earlier comment, you asked whether skipping the curve fit would result in a better focus point (i.e., just select the focus position that provides the smallest HFR). I don't think so. The curve fit provides a valuable role in minimizing noise that would be lost if you just selected the lowest value. Also, the curve fit lets you find the minimum between two measurement points. Of course, the challenge is to get consistent enough data that look like a hyperbolic curve. If you're not seeing a consistent curve, then (a) you're probably not moving far enough out from ideal focus or (b) there is some mechanical slop in the system somewhere that's producing inconsistent focuser positions. I've never used a secondary mirror focuser, so I don't have any insight into errors for that system. A properly operating focusing system should produce a hyperbolic curve, so I think the star detection + hyperbolic fit algorithm works great. Keep experimenting! A good exercise for a full Moon. Thanks for watching!
@@Aero19612 backlash is interesting to algorithm implementation because it factors in fundamentally when you change direction, it definitely can occur if the software is jumping back and forth but if the software sweeps in only one direction or changes direction only once based on steps from starting point, not all the samples should have high noise and not be all crap. For the alg idea the min is just of the samples done, error on the global minima vs sampled minima is determined by the sample step size and you don't need to exploit the v curve shape- it is a more basic optimization strategy for any kind of function with more scenarios it works and gives a result with quantifiable error as well. If it's single pass it will be robust to backlash. Newton rhaphon is another thing you could do but it's more subject to run away error and snr and backlash depending on how the search is done. In the right scenarios v curve fitting is definitely going to give you the best result of the model, noise, and parameters are all tuned but best by repeated direct sampling is simpler and more robust - the result is pretty good and reliable. Also consider we use the same system night to night so we know a range and a good step size for fine tuning, this means you can easily spend say 10 samples quickly and the run to run variation and process/ retry criteria seems more robust than all the things you need to do to assess the v curve which also fail frequently at giving good and consistent results. So if the criteria is did I achieve an autofocus and did I get a good picture , I think both of these stats are improved.
@@Aero19612 also yes I have the mirror locks set. Fastfocus seems to have little backlash already, samples always looked highly repeatable - when you have big slop it is noticable even in manual focus.. this doesn't mean there isn't enough to give algs trouble either but it sets a magnitude. Also optec has built-in backlash compensation too iirc. I think you had a way of determining the backlash in one of your videos based on 2 lines of data around the critical region, I'll have to see what I can pull out of that.
Hi, thanks for your video. In my case, I'm having the points going up and down in both sides, I cannot see a pattern....Can you imagine what it could be?
Hi Alberto. Hmm. There are several possible issues. First, do a rough focus by eye or with a Bahtinov mask. You always want to perform an autofocus run with the scope pretty close to focus. Typically, if you're not seeing a curve, you probably need to increase the autofocus step size so that the maximum out of focus HFR is about 3 to 4 times the lowest HFR. See if that helps and check back in if you're still having issues. Thanks for watching!
I don't recommend the ZWO auto focuser when imaging in cold weather, it freezes. I have the Rigel N-Step system. It's light, doesn't need much space andis reliable down to -25° C. They have brackets available for most scopes, including the SCTS.
Very interesting! I had not heard of a cold sensitivity for the ZWO EAF. Of course, your area is MUCH colder than mine! I rarely see below -5 C. Thanks for watching!
James, I’d just like to say your suggestions and tips hit a home run with me. Thank you for the help.
Thanks for your work and sharing the process and results. Great resource as I recently installed the Celestron V2 focuser on the new C9.25 Edge as my first foray into the autofocus world (after I found out just how touchy that manual focus is even with the Celestron Reducer installed).
My initial runs were absolutely terrible and then I followed your video and was soon getting similar results with a very nice parabolic curve on both sides. I found that 150 for the out backlash setting really did the trick as you suggested, and for my setup, a step size of 50 worked great.
Great! I’m glad you got it working. Nothing more frustrating than to have everything set up and then can’t get good focus. I didn’t know Celestron had a newer version of their focuser. I’ll have to look that up.
Very good and explanatory video my friend. Very useful for SCT users. Keep giving out your expertise. That's what makes this hobby interesting. Solving problems and getting better!!!
Haha. When does the "Getting Better" part start? Thanks for watching!
Every single of your videos sets the standards, thank you.
Hi James, nice video. I have been using Hocus Focus on my C11w0.67 reducer for about a month now with great results. For what it’s worth, I didn’t have to change any of the more advanced settings to get it working well. On the main plug-in configuration page for HF, there’s a setting for “Long FL” and “wide range” for the focus range that’s giving me excellent results. The HF developer even recently added some updates for SCT star detection for accurate HFR measurements even when significantly out of focus (donut stars).
Great feedback, Matt! That’s good to hear…the parameter list looks like a project for a full Moon. It’s nice to hear that there’s a “long focal length” preset. I’m looking forward to digging into it and giving it a trial. Thanks for watching!
Absolutely agree with your comments regarding the Celestron Focus Motor. It's been good for simple focus purposes but I've experienced the same overshoot in backlash and need to over-compensate the values for better autofocus routines.
Great video! Thank you
I cross my fingers every time I have to do an autofocus with it. Thanks for watching, Rowan!
Another great video James! I’ll be trying a few of your tips out for sure, thanks for sharing these!
I just watched your Antlia filter vid. I'm about to buy a set. I laughed when you mentioned the huge halo around Alnitak with the ZWO OIII filter. I know it well. Like any good astrophotographer...I blame the equipment for my less-than-expected results! I'll drop a note on your channel...
Thanks for this my Meade 127 Mak has been giving me the business on auto focus!
I hope it helps. After sorting this out, I’ve been getting very consistent and good autofocus results.
Hi James, bit of an older video but still relevant today. I’ve been experiencing a lot of what you’ve covered here. I have a very high precision electronic focuser, on the order of 7nm steps. I’ve just recently fitted it to an EdgeHD 8 and my step size and overshoot numbers have been very high with HFR being very inconsistent. I’m looking forward to working with some of the additional settings you’ve outlined here.
Cheers!
Doug
There’s light at the end of the tunnel. It probably isn’t a train. Unless it is. That’s astrophotography in a nutshell.
@@Aero19612 haha! Probably the moon! Your discussion on settings led me to my solution, thank you!
Looking good Jay!
Btw, since your last video on this topic, I have been testing Hocus Focus and it operates very well, in fact I am changing it to my primary focusing method. The part I like about it is that it detects all the stars in the image thus you get better averaging of the HFR. Also, because it detects all the stars, using the abberation inspector in NINA helps me adjust for tilt better as now I can see more annotated stats within the ab inspector image; So good job for the creator! The only thing I would hope the creator would do is to allow single star auto focusing. I have been testing a lot of lucky style imaging techniques at focal lengths up to 14,000mm and I really need a single star focusing method. One thing I don't like about Hocus Focus is there seems to be a bug with turning on and off annotation from the image view, some times it doesn't turn on or off so I have to go to their setting tab thus adds another step.
Keep it up buddy!
The curves look much better now. Great to hear about your experience with Hocus Focus! I’ll probably make that switch myself once I get done with a couple of targets with SCT. Then I’ll reconfigure and add the focal reducer and start 2x2 binning. At that point, I’ll dial in the settings for Hocus Focus. I hope you mean you’re imaging at 1400 mm! Haha. I think the Hocus Focus algorithm is being actively developed and the SCT focal range is the last to get any love. I’m optimistic about though.
Great video. Waiting to learn more about Hocus Focus.
Thanks, Ernie! I'll wait to tackle the Hocus Focus settings after I reconfigure my SCT with the focal reducer and 2x2 binning. I have to finish up M1 and M81 in the current config (no FR and 1x1 bin) before I switch. There's a ton of fiddly-looking parameters in Hocus Focus right now. I hope that as experience with it grows, the plugin can "tune" itself for a given imaging setup. We shall see.
Thank you for the video. It gave me some great ideas. I have an edgehd 14 with no reducer, and perhaps unsurprisingly the narrow band filters are a problem. I can double bin, but if I triple bin my uncertainty gets huge.
@@matthewbrown8679 Uggh. A C14 is a challenge. A set of par focal filters is a blessing. If you can focus with the Lum filter and simply switch to Ha, O3, and S2 that eliminates a lot of heartache. Good luck!
Excellent topic and great video as always James. I bought the Celestron motorized focuser when it first came out. For the most part, it works fine but every so often it glitches and my curve looks awful. You've provided a few great tips and I might look to the Pegasus or ZWO in the future. Clear Skies!
Glad you're having a (mostly) trouble-free experience with Celestron's focuser. Very frustrating when equipment issues put a stop to an otherwise good night for imaging. Arghh. Thanks for watching, David!
I use the EAF on my circa 1983 Celestron C8. As I commented in your earlier video, I set the backlash value *way* high, some 3-4x the actual backlash value. I set is such to be always "pushing in" on the mirror. That extra mirror movement, at least for me, eliminates the wonky focus off-curve steps that I sometimes got similar to what you showed.
Yep. That seems to do the trick for me as well. Could be that in vs out is a smaller factor than the magnitude of overshoot move. Hey, when it starts working, I stop asking questions. Thanks for watching, Bruce!
Hi Bruce
How do set auto focus so that last adjustment is push in ?
@@BruceMallett
Makes sense. Seems straight forward enough now. Really appreciate the info. Your after saving me quite a few hours. I’d be going down that “Rabbit hole” as James would put it, been down there enough 😁
Hi James. Thanks for a great Vid.
One question: you set your AF step size to 20. Isn't that way too low for a SCT. My C9.25 and my RASA8 require a lot of focuser movement to get the focus to budge, a design feature of SCTs. Wouldn't that create a very shallow curve if it worked at all? But apparently it works for you, so what am I missing?
Thanks - Tommy
Well, the step size depends on the mechanical focuser in the SCT and the gears in the focus motor. I'm using the Celestron Focus Motor (I'm not a big fan) which is much more coarse than, say, a ZWO EAF or a Pegasus Astro FocusCube. So it takes fewer steps with the Celestron focuser to sweep through a range of HFR values (I try to limit the range to 3 times the optimum HFR). If you're using a different electronic focuser, then your number of steps may be different. Experiment, Experiment, Experiment! Thanks for watching, Thomas!
Another really interesting video. I’ll be looking into some of those parameters to adjust for my 10” Meade SCT. I used to have a fairly crappy Crayford focuser and was not getting great results and in the end forked out for the Primalucelab Esatto 2” focuser so now i lock the primary mirror and let the Esatto do it’s thing and it seems to be producing nice consistent curves. I just had to get my head around using a step size of 6000 steps with this focuser :)
That's the way to go, Logan! I wish I had one of those after all of the other issues I've had with the Celestron focuser. Haha, I think 6000 steps would have me scratching my head too. Must have VERY fine steps. Clear skies!
I started from Essato as well. Sold it and got Moonlite. I also saw in action Optec, which cost fortune. No company bits Moonlite.
great video. I have heard that using a combo of hyperbolic + Trends is a good option, any thoughts on that? I recently got a Moonlite focuser/rotator and I'm wondering if the backlash needs to be adjusted to a lower value now...(I have a Esprit 120 refractor), guess I need to do trial and error testing.
Hey Greg. My view is that an ideal data set (HFR vs focuser pos) “looks” like a hyperbola. If you go waaay out of focus (assuming the HFR estimation algorithm still works), the hyperbola approaches linear asymptotes that look like the crossing trend lines. But you have to go waaay beyond focus and probably should throw out the data near optimum focus. In summary, I don’t like dual fit approach (please note that me not liking it doesn’t mean it’s bad!). I try to keep my autofocus runs in the range where the hyperbolic curve applies and, hence, never go so far out of focus that I capture the asymptotes. I stick with the hyperbolic fit and try to generate the bast noise-free HFR/position data set that I can. Congratulations on the Moonlite focuser! I don’t have one, but sounds like they make awesome stuff. So, yeah, probably want to revisit the backlash setting. Then again, if you get good performance, there no need to change anything. Thanks for watching!
Your apparent knowledge of these complex auto-focus parameters is academic. It's hard to image where all this know-how came from! I have to just follow along and hope it gradually sinks in across multiple viewings.
I have the difficult and challenging RASA 8, does it count as a SCT? And of course, no EFW and no focal reducers and no binning.
My tilt is nothing short of terrible, in fact "extreme" as noted by ASTAP numerous times. I have ZWO 2600s, the MC and MM. Both show the same tilt depictions and in both of them, the tilt moves with the camera rotation of 180 degrees. I also have the ZWO EAF, so I am now switching from the ASIAIR Pro to NINA in order to get some help and use Hocus Focus. Of course my corner stars are out of focus donuts, but they are also pulled into eggs. Not pretty at all. I tried 2 different camera adapters, both said to produce ideal back focus, but neither improved the corner stars. I am trying thin shims to try back and forth to find a back focus that the rig likes, since it doesn't care about "ideal". And I will investigate collimation, though I don't believe my scope is SO far off to be producing the results i get.
I hope that your videos and Hocus Focus will give me at least some clue as to where this bad tilt is coming from. You indicated that it is really for refractors, which I would think are less tilt prone to start with.
Many are using Hocus Focus with the hyper-expensive "Octopi" in order to basically adjust out the tilt, regardless of where it's coming from. Problem being, that's for ONE camera only, and I have two. I don't think its right to simply give up LRGB imaging for the octopi.
Thanks for your amazing expertise, ha, I will send you my RASA!!
Hey Paul,
As you know, I don't have a RASA. If it's not a form of SCT, it's awfully close. Of course, the RASA is used like an SCT with a Hyperstar system (imaging at the secondary mirror location). But, I gather, you do focus by moving the primary mirror (right?), so some of those same challenges. Most comments about the RASA I hear are very positive. How are you able to rotate your camera? Rotator? I've seen a few people use Hocus Focus tilt measurement to guide their tuning efforts (seems very useful). But of course, you've got to have a tilt-adjustment capability. I have not used that feature of Hocus Focus (yet). Have you looked at other tilt adjustment components? The Octopi looks pretty expensive. Sorry I'm not any help here. You're in uncharted territory for me. Good luck!
@@Aero19612 Yes, the RASA is great and fast. But, it has a tiny range of back focus which is critical and hard to get right. And perhaps my ASI2600s aren't a good match for it. I tried to ignore my corners and crop them out, I had to learn other stuff. But when I got slightly proficient, the bad stars couldn't be ignored. I'm trying to learn NINA to help with this problem. I'm not sure my problems are fixable regardless of what I do.
Camera rotation is a total pain on the RASA. Remove dew shield, reach in there to twist camera when it's got 3 wires attached. Dont push or pull! Don't unscrew the camera and mess up the back focus! It can be done, but not easily. Ha, you have to be desperate.
My problems aside, I wish to read more about your knowledge of star quality. Wish I knew that stuff!
Great work - I'm going to start saving focus runs (with Hocus Focus) so the next morning I can view the actual focus images and maybe learn more about why some of them are 'bad'. At 2000mm (my SCT) I assume some of it is just an ill-timed gust of wind or cable tug - or even seeing
Yes. That's a great feature that Hocus Focus offers. Do you look at the stored autofocus curves like I show in the video? Those can also provide some insight.
Thanks, great presentation.
Thanks for watching! Amazing what a few correctly set parameters can do!
I have the optec fastfocus secondary mirror focuser - this issue will remain. It's not mirror flop for me either and I really don't think it's backlash. Gotta be donut + optical artifacts specific to the optical design that throws the algs off. What happens to the donut near or after focus, particularly if you can't get all stars on the massive imaging region in focus at the same time... maybe after it crosses critical values the donut/inverted donut artifact throws off the hfr/fwhm analysis.
Hi Jason. SCT focusing is a challenge, for sure. Some SCTs more than others. One of the problems, is that the mechanism that moves the primary mirror has to have some free play and can't be observed because it's concealed in the tube. Your secondary mirror focuser should get around that (one would think). Do you have primary mirror locks on your SCT? For me, I guess I'm lucky, cranking up the backlash number really helped to sort things out and I got good focus results from then on. In an earlier comment, you asked whether skipping the curve fit would result in a better focus point (i.e., just select the focus position that provides the smallest HFR). I don't think so. The curve fit provides a valuable role in minimizing noise that would be lost if you just selected the lowest value. Also, the curve fit lets you find the minimum between two measurement points. Of course, the challenge is to get consistent enough data that look like a hyperbolic curve. If you're not seeing a consistent curve, then (a) you're probably not moving far enough out from ideal focus or (b) there is some mechanical slop in the system somewhere that's producing inconsistent focuser positions. I've never used a secondary mirror focuser, so I don't have any insight into errors for that system. A properly operating focusing system should produce a hyperbolic curve, so I think the star detection + hyperbolic fit algorithm works great. Keep experimenting! A good exercise for a full Moon. Thanks for watching!
@@Aero19612 backlash is interesting to algorithm implementation because it factors in fundamentally when you change direction, it definitely can occur if the software is jumping back and forth but if the software sweeps in only one direction or changes direction only once based on steps from starting point, not all the samples should have high noise and not be all crap. For the alg idea the min is just of the samples done, error on the global minima vs sampled minima is determined by the sample step size and you don't need to exploit the v curve shape- it is a more basic optimization strategy for any kind of function with more scenarios it works and gives a result with quantifiable error as well. If it's single pass it will be robust to backlash. Newton rhaphon is another thing you could do but it's more subject to run away error and snr and backlash depending on how the search is done. In the right scenarios v curve fitting is definitely going to give you the best result of the model, noise, and parameters are all tuned but best by repeated direct sampling is simpler and more robust - the result is pretty good and reliable. Also consider we use the same system night to night so we know a range and a good step size for fine tuning, this means you can easily spend say 10 samples quickly and the run to run variation and process/ retry criteria seems more robust than all the things you need to do to assess the v curve which also fail frequently at giving good and consistent results. So if the criteria is did I achieve an autofocus and did I get a good picture , I think both of these stats are improved.
@@Aero19612 also yes I have the mirror locks set. Fastfocus seems to have little backlash already, samples always looked highly repeatable - when you have big slop it is noticable even in manual focus.. this doesn't mean there isn't enough to give algs trouble either but it sets a magnitude. Also optec has built-in backlash compensation too iirc. I think you had a way of determining the backlash in one of your videos based on 2 lines of data around the critical region, I'll have to see what I can pull out of that.
Hi, thanks for your video. In my case, I'm having the points going up and down in both sides, I cannot see a pattern....Can you imagine what it could be?
Hi Alberto. Hmm. There are several possible issues. First, do a rough focus by eye or with a Bahtinov mask. You always want to perform an autofocus run with the scope pretty close to focus. Typically, if you're not seeing a curve, you probably need to increase the autofocus step size so that the maximum out of focus HFR is about 3 to 4 times the lowest HFR. See if that helps and check back in if you're still having issues. Thanks for watching!
@@Aero19612 yes, it helped. Now I got a decent curve. thanks!
Great, Alberto!
I don't recommend the ZWO auto focuser when imaging in cold weather, it freezes. I have the Rigel N-Step system. It's light, doesn't need much space andis reliable down to -25° C. They have brackets available for most scopes, including the SCTS.
Very interesting! I had not heard of a cold sensitivity for the ZWO EAF. Of course, your area is MUCH colder than mine! I rarely see below -5 C. Thanks for watching!
I'm not finding where to set the Image Stretch Factor and Black Point, can you tell me where I got set these? Thanks
Hi Dennis. Select "Options", "Imaging", and then "Advanced Settings" under "Image Options".