I have gathered more data on Centaurus A and have stacked the best 10 hours out of 19 in total. Image is cropped and a little coma still persists due to poor collimation on one or two of the nights (I'm working on it).
If the title of the thread confuses you, it's because in my last post I mentioned that the dust lanes look a little like a bottle of champagne being popped! Such a unique and fascinating target.
Comments are most welcome. Image on the right has a little more saturation.
Stephane,
This is an excellent image and worthy of the Deep Space section
Detail is tremendous and colour spot on
Well done !!
If it’s any help, my Coma issues were resolved using a distance of 57mm to 57.5mm from CC to sensor face
8”f5 GSO newt and Baader MPCC Mk3 using my 2600MC
Baader recommend 55mm +- 1mm but this didn’t work for me
I kept adding 0.5mm spacers from Sidereal Trading until I found the sweet spot and coma was totally eliminated
Cheers
Martin
Martin, your comment about 57-57.5 mm is very helpful. I am currently 56-ish, and I still feel it’s not enough, so your experience reassures me. I also need to improve my collimation technique. I am getting better collimation by adjusting the concentrique circles of an out of focus star, than with the laser collimator. HFR has improved significantly since all the DIY and guiding has also improved since bolting the guide scope to the Losmandy bar you recommended. Thanks to everyone for all the tips.
Gorgeous. Interesting noise pattern though. Are you dithering?
Thanks Adam. I dither only every 10-15 subs. I used to dither every 2 subs. I’ve heard many differing opinions on dithering. Any advice? Also, please point out the noise pattern you can see. I’m not sure what to look out for and can’t see it.
Thanks Adam. I dither only every 10-15 subs. I used to dither every 2 subs. I’ve heard many differing opinions on dithering. Any advice? Also, please point out the noise pattern you can see. I’m not sure what to look out for and can’t see it.
I dither every 2 or 3 subs. What was the advise you received to dither 10-15? You're basically locking in the noise profile of your camera for 10-15 subs and stacking that. That's a lot of noise.
Adam, I am told that the star trailing for cheaper mounts naturally spreads out the noise even without dithering. I think I can see the noise pattern you pointed out, but not sure it is in the higher resolution version. Maybe the jpg compression did this?
Here’s a link to a higher resolution. Your observations would be much appreciated. If you can still see the pattern, please let me know.
That higher res version is definitely what you should have posted initially! Wowzers, a great image now even better.
Mottling is still in that image, but much less apparent. So you're probably half right; a lot of what I see above is from jpeg compression, but the mottling exists in your higher res file.
Also, not sure I agree with that advice about lower quality mounts. If you're trailing to get rid of fixed pattern noise, then it will show in your stars. Your stars are about perfect, so any deviation in your worm cycle isn't helping reduce noise.
and by the way, I know this is the "beginners forum" (you need to move to Deep Space btw, your images are great), and I don't generally give too much advice unless asked. You always seem up for a bit of constructive criticism, hope that's okay.
Anyway, make sure to post your higher res versions next time! This forum kills images with compression.
Stephane,
In regard to dithering I agree with Adam
I’ve tried dithering my image every 3rd or 4th or higher, and it’s a waist of time, even if you set an aggressive dither of say 6 to 10 pixels
I dither every image from 60 sec to 300 sec subs and it works well
I set my dither to the lowest value in APT which is 1 ( equates to 2 to 4 pixels ) and set my dither settle to 15 sec and it works well on the EQ6-R mount , mount responds well and images are free of any fixed pattern noise.
The only limiting factor with dithering is when sky conditions are atrocious and your guiding is see sawing at say 1.50 arc sec , dithering will upset your mount even further and Dec may not recover until the next sub. These EQ6-R mounts are good but not in the same league as higher end more expensive mounts, EQ6-R’s do have inherent Dec backlash. I’ve tuned my Dec backlash down to 900ms which I can live with. All EQ6-R’s are not the same due to manufacturing and limiting QA. Some folk are lucky and get a good mount that can be tuned well , other folk are not so lucky and can’t get below 2000ms of Dec backlash.
Also PA is super important so try and get your PA down to below 2 arc minutes
Don’t just rely on the numbers on the dashboard from your software , perform a progressive 60 sec to 90 sec sub test on a Star. If you can get to +60 sec without any loss of Star shape with that 8” f5 newt , then your fine
Poor PA has a knock on affect with everything in AP
With time and experience you will get to know some gremlins which sometimes appear with your mount and scope
Well done again !!
Martin
Adam, thanks so much for the encouragement and for the invitation to post on the Deep Space section. Yes, I appreciate constructive criticism as I am always trying to learn and improve. Of course, experience can't be rushed, but having help along the way certainly helps. Thanks again.
Martin, in regards to dithering, thanks for sharing your experience. I used to dither regularly, but got really eggy stars (Remember my Sombrero image?). Seeing might have coincidentally been really bad for those nights. I've also learnt to go slightly East and North heavy to encourage one-way corrections rather than to be slightly off polar alignment which some people do to encourage one-way guiding corrections. My guiding has improved from about 0.7-0.8 to 0.5-0.6ish. So far though, I feel that dithering hurt my images more than the benefits it brings. I'll have to experiment further though given your and Adam's comments. In regards to dec backlash, I have done some tuning thanks to the Cuiv video you once mentioned. I believe this also helped a lot with my improved guiding, as I tuned as much as I could, but without causing any binding. However, I haven't actually measured the backlash in PHD2. Now you have mentioned your figure of 900 ms, I am curious to see where my mount stands. Thanks for all the tips and encouragement, they are very much appreciated.
