I've been following you for some time and despite not having the same equipment or issues, I really enjoy all your videos and the way you approaches the issues/topics you show. All of them are very informative, technical, detailed and nerdy (in the good way!), you must spend a lot of time preparing them but it really worth it. If you allow me a comment, I miss some videos about data processing. If you are as thorough as with equipment, they really must pay off!
Hi Aleixandrus, Thanks for following along! Yes, I need to do more processing videos. That's also an area where I need to improve. There are lots of good processing videos out there, so I typically feel I'm not adding much to the conversation. Most other RUclipsrs aren't that interested in the nerdy engineering stuff that I tend to do here. But I'll try!
Hi James, First of all, THANK YOU for that shoutout on my Tulip Nebula and the Black Hole with the Bow Shock video. I have the 0.7x reducer for the 11" EdgeHD and yes, it is very difficult to get the back focus correct (146mm). It seems with my setup, to achieve perfect back focus, I have to put the focuser nearly all the way out to its limit. Then, the autofocus won't work because it wants to go out beyond that limit to start the process. That Antlia H-beta-S2 filter looks very enticing. I will look into that. I like that blue that is in that region of the spectrum.
That's crazy about having to have the focuser all the way. Is that a design issue, do you think? As for the blue at H-beta: I just used that filter for the first time last night and do see a distinct blue and distinct red. More on that later... Happy imaging!
Great video as always. Star colors are hard at times. Have found that removing stars as the first step and then color correcting just the stars, then going back to original stack, color correct and background extract that image, “destar” that image and then combine the two will give you nicer more realistic star colors. More work but what isn’t?
I agree. I usually do that and thought I did here, but then this is the first pass through these data so I may have skipped some steps to save time. Thank for watching, CJ!
@@Aero19612 my current primary target is the bubble! I got 1.5hrs of Ha O3 and my next session will be S2 O3. I have the Askar D1 and D2 set as well. I will have to throw in some of the Antlia S2 Hb data maybe. I should collect more data than I have, but I have had fun exploring different targets since I started last fall. Thanks for all your work and what you share.
I don't doubt it. There seems to be a lot play in the back focus for this reducer. I just changed mine by 4 mm (101 mm back focus) and still could use a shorter back focus. May have to try a big reduction and see what happens. Thanks for watching!
Right. I'm in a race. I need two nights to get some H_beta-Sii data with the new filter and a brief opening between clouds on the third night for some experimenting with the focal reducer back focus. Then I'll be down for maybe two weeks. Keep your fingers crossed!
Im using the Antlia dual band filters. HaO3/S2Hb and getting very good results. Im in Bortle 5-6 and have had good results in full moon. Clear skies! edit... using Askar FRA400 and ASI2600MC
Yep. I bought the Antlia HbSII after this video and gave it a go along with my OIIIHa filter. See the next vid in the list if interested. I really like the combo for tru SHO(plus Hb).
Hi James . Very interesting Video as usual . You can always tell when someone processes the Crescent Nebula correctly,,,you get to see the perfect black hole in the middle of the Nebula . I searched for this online without success . Maybe you'll have more luck . BTW , did you know that Antlia has an OAG with a built-in Filter Drawer , Helical Focuser and 12x12mm Prism ? Interesting Product . Thanks again ./SRK
Hi Ranjit. I doubt that this filter would be good for visual observing. It just lets a little light through. It might be OK for Electronically Assisted Astronomy, where images are continually added in real time to produce an image. Thanks for watching!
Thanks, Ron! The rule goes: if the stars point in toward the center of the image, you need to increase the back focus. If the stars are tangent to a circle centered on the center of the image, then you need to reduce the back focus. The latter matches what these stars are doing.
@@Ronbo765 Absolutely. That's where I get such random numbers for my actual focal lengths: 1318 mm with the focal reducer and 2312 mm without the reducer. I also put these numbers in PHD2, NINA, and Stellarium.
@@Aero19612 I did not know about the orientation of stars to determine inside/outside optimal backfocus! BtW Optcorp has a nice diagram demonstrating the effect. To be clear, do you mean you get random focal length numbers on the same optical set up? Perhaps that is a function of seeing conditions during the plate solve? Does it vary during multiple exposures over a few minutes? I find it very odd that people get such big backfocus deviations. The Celestron EdgeHD white paper shows a deviation from nominal of < .5 %. Must be the focal reducer causing the variance. You could always transition to a Hyperstar !
Haha. No, it's not that random. I mean the C9.25 has an advertised focal length of 2350 mm, I get 2312 mm. With the reducer/corrector it's supposed be 1480 mm, but I get 1318 mm. The numbers are constant for a given back focus. Add or remove back focus and the actual focal length will change.
Regarding the Celestron 6.3 focal reducer, the 105mm back focus is the spec for the C8 OTA. The C9.25 is a different beast. I use 86mm back focus and I have pretty sharp stars in the corners. My suggestion is to reduce the back focus distance and plate solve until you reach 2350 * 0.63 = 1480mm.
Hi Dan. I partly agree. An optical element like the focal reducer/corrector should have the same back focus for scopes with essentially the same F-numbers (directly related to the angle the incoming light makes with the lens). So, the reducer/corrector with the C8 at F/10 should require the same back focus as the C9.25 at F/10. Another commenter on this thread noted that he found a back focus of 85 mm (sound familiar?) is required for best results with his C8. I changed mine to 100 mm and tested and concluded that was still too high. I think you're both correct: 85 mm is closer to the true back focus for this 0.63 reducer. Thanks for watching!
@@DrunkferretKG People keep mentioning 105mm more because that's the number for the C8, and many of them are visual observers who can't plate-solve. Celestron has clarified on multiple forums that 105mm is specific to the C8. Additionally, Starizona states C8 is closer to f/11 and their SCT Corrector IV 0.63x reducer yields f/7.1 on C8 and f/6.5 on C9.25, so there is a difference between the OTA's. If you place your sensor with a focal reducer at 105mm on a C9.25 and you get a focal ratio of f/5.6, and your stars look elongated it's clear that the spacing is too long. You will be much happier at around 85mm because in addition to stars looking better you'll also get less vignetting in the corners.
Here's the data I've collected on my C9.25 + Celestron f/6.3 reducer vs back focus distance: 106mm => FL = 1381 => FR 0.588 95mm => FL = 1436 => FR 0.611 88mm => FL = 1467 => FR 0.624 86mm => FL = 1482 => FR 0.631 84mm => FL = 1489 => FR 0.634 79mm => FL = 1516 => FR 0.645 Back focus distance is measured from the point where the diameter of the reducer drops, right before the threads start. Different adapters might thread more or less on the threads, but the flange is a fixed point.
@DanPechiu thanks! That give a good perspective for me. I just got my C8 SCT setup again after running a 65PHQ for a while. My back focus is at 106.5mm and plate solving gave me 1276-1277mm(different targets). The math says it should be 1278.9mm. If I order some more parts I might be able to shave off that 1.5mm or I could change a spacer and subtract 5mm. Stars are good with just a bit of distortion at the corners of my Asi294mcp. I have already done flats for my filters so I have to find the motivation to change it again.
There are areas of sky that I just cannot get autofocus with Ha and O3 on Edge 9.25 with or without reducer. One of such area is around Cat’s eye nebula. To get autofocus, I need whooping 45 sec exposure for every point! I had once conventional SCT 8” one). Starizona reducer is by miles better than Celestron one.
I've imaged the Cat's Eye, so I have run into that problem. 45 sec is a long time. Are you guiding during the auto focus run? I've heard that the Starizona is much better.
@@Aero19612 I don’t guide, but mount tracks constantly. It is built in function in the mount. It doesn’t track when slew, when it has settled it starts to track right away.
I have two of these filters which I use with my QHY268Cs. I have one setup on my 100mm Esprit and the second on my 8”EdgeHD. I love it but I find my background is a tad green. I can work on it with masks but I’m curious to hear if anyone else has this problem.
Yes, the raw image is green. That's normal. Are you performing background neutralization? That will align the median background levels for all channels to the same value and you'll have a neutral background instead of green.
I've been following you for some time and despite not having the same equipment or issues, I really enjoy all your videos and the way you approaches the issues/topics you show. All of them are very informative, technical, detailed and nerdy (in the good way!), you must spend a lot of time preparing them but it really worth it. If you allow me a comment, I miss some videos about data processing. If you are as thorough as with equipment, they really must pay off!
Hi Aleixandrus,
Thanks for following along! Yes, I need to do more processing videos. That's also an area where I need to improve. There are lots of good processing videos out there, so I typically feel I'm not adding much to the conversation. Most other RUclipsrs aren't that interested in the nerdy engineering stuff that I tend to do here. But I'll try!
@@Aero19612 Oh, take that as a suggestion! You can add processing videos but please keep publishing engineering nerdy stuff :)))
Thanks for the informative video James, Can't wait to see how the S2 Hb filter goes.
Hopefully soon if the clouds stay away...
Hi James,
First of all, THANK YOU for that shoutout on my Tulip Nebula and the Black Hole with the Bow Shock video.
I have the 0.7x reducer for the 11" EdgeHD and yes, it is very difficult to get the back focus correct (146mm). It seems with my setup, to achieve perfect back focus, I have to put the focuser nearly all the way out to its limit. Then, the autofocus won't work because it wants to go out beyond that limit to start the process.
That Antlia H-beta-S2 filter looks very enticing. I will look into that. I like that blue that is in that region of the spectrum.
That's crazy about having to have the focuser all the way. Is that a design issue, do you think? As for the blue at H-beta: I just used that filter for the first time last night and do see a distinct blue and distinct red. More on that later... Happy imaging!
Great video as always. Star colors are hard at times. Have found that removing stars as the first step and then color correcting just the stars, then going back to original stack, color correct and background extract that image, “destar” that image and then combine the two will give you nicer more realistic star colors. More work but what isn’t?
I agree. I usually do that and thought I did here, but then this is the first pass through these data so I may have skipped some steps to save time. Thank for watching, CJ!
James that's a lovely M27 image, I like it a lot.
Thanks Paul! I was surprised by the colors and brightness. Still need to work on the detail though. Good task for cloudy nights.
I had the exact same thought. I ordered my Antlia filters a few weeks back to use with my new Duo mc.
Hopefully, I'll see my first results by the end of this week. Thanks for watching, Mark!
Excellent 👌
Thanks for watching, Christophe!
I have the S2 Hb filter and like it very much. The Cygnus Wall is really nice with it!
Good to hear. Thanks Kelly! I'll try it on the Bubble Nebula - doing the Oiii-Ha now.
@@Aero19612 my current primary target is the bubble! I got 1.5hrs of Ha O3 and my next session will be S2 O3. I have the Askar D1 and D2 set as well. I will have to throw in some of the Antlia S2 Hb data maybe. I should collect more data than I have, but I have had fun exploring different targets since I started last fall. Thanks for all your work and what you share.
Will be interesting to see results on the Celestron Reducer backfocus, 85mm seem to work well on the C8/f6.3 reducer and my533mc-p.
I don't doubt it. There seems to be a lot play in the back focus for this reducer. I just changed mine by 4 mm (101 mm back focus) and still could use a shorter back focus. May have to try a big reduction and see what happens. Thanks for watching!
Please keep in touch about the 105mm back focus and what you find out.
Right. I'm in a race. I need two nights to get some H_beta-Sii data with the new filter and a brief opening between clouds on the third night for some experimenting with the focal reducer back focus. Then I'll be down for maybe two weeks. Keep your fingers crossed!
Great vídeo
Thanks for watching, Guillermo!
I'm looking at your exposure of crescent,it states 20 subs @200 sec=28.9 hours?but very gorgeous pics.
Hey Tom. Weird. The video shows "520 subs @ 200 sec". Could it be the resolution you're viewing the video at? Thanks for watching!
Im using the Antlia dual band filters. HaO3/S2Hb and getting very good results. Im in Bortle 5-6 and have had good results in full moon. Clear skies! edit... using Askar FRA400 and ASI2600MC
Yep. I bought the Antlia HbSII after this video and gave it a go along with my OIIIHa filter. See the next vid in the list if interested. I really like the combo for tru SHO(plus Hb).
Hi James . Very interesting Video as usual . You can always tell when someone processes the Crescent Nebula correctly,,,you get to see the perfect black hole in the middle of the Nebula . I searched for this online without success . Maybe you'll have more luck . BTW , did you know that Antlia has an OAG with a built-in Filter Drawer , Helical Focuser and 12x12mm Prism ? Interesting Product . Thanks again ./SRK
Very interesting about the Antlia OAG. I'll look into it. Thanks!
Wonderful video . Is it possible to use this filter for visual observation ?
Hi Ranjit. I doubt that this filter would be good for visual observing. It just lets a little light through. It might be OK for Electronically Assisted Astronomy, where images are continually added in real time to produce an image. Thanks for watching!
Thanks for the reply.@@Aero19612
Beautiful images. How do you know if your backfocus is over the stated 105mm requirement? Could it not be under?
Thanks, Ron! The rule goes: if the stars point in toward the center of the image, you need to increase the back focus. If the stars are tangent to a circle centered on the center of the image, then you need to reduce the back focus. The latter matches what these stars are doing.
@@Aero19612 Celestron with this backfocus issue! Have you ever done a platesolve on your optical train to get an effective focal length?
@@Ronbo765 Absolutely. That's where I get such random numbers for my actual focal lengths: 1318 mm with the focal reducer and 2312 mm without the reducer. I also put these numbers in PHD2, NINA, and Stellarium.
@@Aero19612 I did not know about the orientation of stars to determine inside/outside optimal backfocus! BtW Optcorp has a nice diagram demonstrating the effect.
To be clear, do you mean you get random focal length numbers on the same optical set up? Perhaps that is a function of seeing conditions during the plate solve? Does it vary during multiple exposures over a few minutes? I find it very odd that people get such big backfocus deviations. The Celestron EdgeHD white paper shows a deviation from nominal of < .5 %. Must be the focal reducer causing the variance. You could always transition to a Hyperstar !
Haha. No, it's not that random. I mean the C9.25 has an advertised focal length of 2350 mm, I get 2312 mm. With the reducer/corrector it's supposed be 1480 mm, but I get 1318 mm. The numbers are constant for a given back focus. Add or remove back focus and the actual focal length will change.
Regarding the Celestron 6.3 focal reducer, the 105mm back focus is the spec for the C8 OTA. The C9.25 is a different beast. I use 86mm back focus and I have pretty sharp stars in the corners. My suggestion is to reduce the back focus distance and plate solve until you reach 2350 * 0.63 = 1480mm.
Hi Dan. I partly agree. An optical element like the focal reducer/corrector should have the same back focus for scopes with essentially the same F-numbers (directly related to the angle the incoming light makes with the lens). So, the reducer/corrector with the C8 at F/10 should require the same back focus as the C9.25 at F/10. Another commenter on this thread noted that he found a back focus of 85 mm (sound familiar?) is required for best results with his C8. I changed mine to 100 mm and tested and concluded that was still too high. I think you're both correct: 85 mm is closer to the true back focus for this 0.63 reducer. Thanks for watching!
I keep seeing 85mm pop up, but it seems to be drowned out by the 105mm recommendations. I have to go back and watch some of your videos on this James.
@@DrunkferretKG People keep mentioning 105mm more because that's the number for the C8, and many of them are visual observers who can't plate-solve. Celestron has clarified on multiple forums that 105mm is specific to the C8. Additionally, Starizona states C8 is closer to f/11 and their SCT Corrector IV 0.63x reducer yields f/7.1 on C8 and f/6.5 on C9.25, so there is a difference between the OTA's. If you place your sensor with a focal reducer at 105mm on a C9.25 and you get a focal ratio of f/5.6, and your stars look elongated it's clear that the spacing is too long. You will be much happier at around 85mm because in addition to stars looking better you'll also get less vignetting in the corners.
Here's the data I've collected on my C9.25 + Celestron f/6.3 reducer vs back focus distance:
106mm => FL = 1381 => FR 0.588
95mm => FL = 1436 => FR 0.611
88mm => FL = 1467 => FR 0.624
86mm => FL = 1482 => FR 0.631
84mm => FL = 1489 => FR 0.634
79mm => FL = 1516 => FR 0.645
Back focus distance is measured from the point where the diameter of the reducer drops, right before the threads start. Different adapters might thread more or less on the threads, but the flange is a fixed point.
@DanPechiu thanks! That give a good perspective for me. I just got my C8 SCT setup again after running a 65PHQ for a while. My back focus is at 106.5mm and plate solving gave me 1276-1277mm(different targets). The math says it should be 1278.9mm. If I order some more parts I might be able to shave off that 1.5mm or I could change a spacer and subtract 5mm. Stars are good with just a bit of distortion at the corners of my Asi294mcp. I have already done flats for my filters so I have to find the motivation to change it again.
There are areas of sky that I just cannot get autofocus with Ha and O3 on Edge 9.25 with or without reducer. One of such area is around Cat’s eye nebula. To get autofocus, I need whooping 45 sec exposure for every point!
I had once conventional SCT 8” one). Starizona reducer is by miles better than Celestron one.
I've imaged the Cat's Eye, so I have run into that problem. 45 sec is a long time. Are you guiding during the auto focus run? I've heard that the Starizona is much better.
@@Aero19612 I don’t guide, but mount tracks constantly. It is built in function in the mount. It doesn’t track when slew, when it has settled it starts to track right away.
Intéressant pour mon hyperstar c11..
If you're using a hyperstar, be sure to get the correct version of the filter. There's one for "fast" scopes and one for "slower" scopes like mine.
I have two of these filters which I use with my QHY268Cs. I have one setup on my 100mm Esprit and the second on my 8”EdgeHD.
I love it but I find my background is a tad green. I can work on it with masks but I’m curious to hear if anyone else has this problem.
Yes, the raw image is green. That's normal. Are you performing background neutralization? That will align the median background levels for all channels to the same value and you'll have a neutral background instead of green.