Keen for some advice on this one. It's my first image after a reasonable polar and drink alignment.
Stellarvue SV105 f/6.2 APO
Canon 450D unmodded
400 ISO
2 minute subs
20 minutes total exposure
No darks
Out to the right of the image the stars look elongated. Is this what you call coma or something else?
Cheers,
Carl
Hi Carl, I have had a quick process on your image. The unequal stars would probably be caused by your camera not sitting quite square in the focuser or the focuser sagging a little. Overall the image could use a bit more exposure but as it is you have done quite well. I would have been very happy to get an image like this when I started imaging.
I probably would have said the same as Doug, Possibly the camera not sitting square or focuser sag.
Having said that, you've picked up some great data (as Doug's repro shows) and should be very encouraged about your future prospects! That set up is going to provide some nice images. Well done!
Carl while I have no experience of using SLR cameras for astrophotography, the lack of symmetry of the elongation points to something like how the camera is mounted. Short of taking another image to see if it appears again I have no other suggestions. A great image nevertheless.
Thanks for all the comments folks. I really appreciate it. I'll take a closer look at the camera mount and focuser next time to see if I can pinpoint what's happening there.
Doug, thanks so much for reprocessing my image. It's useful to see what others can get out of it. Curious that the colour is different and you've manage to keep away much of that reddish noise. Hmm ... time for more practice me thinks!
Thanks for all the comments folks. I really appreciate it. I'll take a closer look at the camera mount and focuser next time to see if I can pinpoint what's happening there.
Doug, thanks so much for reprocessing my image. It's useful to see what others can get out of it. Curious that the colour is different and you've manage to keep away much of that reddish noise. Hmm ... time for more practice me thinks!
Cheers,
Carl
Hi Carl, The biggest tip I can give you at this stage is to keep an eye on the histogram when processing an image. Try to keep the histogram close to the left hand wall of the histogram and adjust each colour using levels to align all 3 colours with each other and close to that left hand wall (0 end of the histogram) (black point).
I have used curves to start with in photoshop and increased the bottom number to 13 and the left hand side number to 65 and then do the flatten of with about three more points.
Then levels but i open up the histogram and individual colours to the left hand side without cutting any off.
Repeated a cople of more times but less aggressive with the curves and then flatten, then smart sharpen advanced with numbers in first in Sharpen 80, 3,6 and Lens blur in drop down. In both Shadow and Highlight had numbers on 50, 50 and 20. Then filter and remove noise. I hope it helps.
I spent some time last night taking some more subs for this one. This time I have 20 subs of 2minutes each at 400 ISO. I only got 10 darks and no flats.
I can now see a little more of the internal structure and some more "wispiness" at the ends. Slowly getting better I think.
I remember my first image of this object and we sort of could maybe possibly see the galaxy shape with star trails prevelent and was thrilled so your image is about 10000 times better than mine.
I think initially when I processed an image I would try to process more than the data would allow and I think this is what you have done here in your excitement. The very distinctive white round sphere should not be there and shows you have pushed your data too much. A rule of thumb I use in phtoshop is increase the curves initially so the numbers on the x axis are 13 and the y axis is 65 and then I soften the curve to make the dog leg shape. Then go for levels of esch channel. Then repeat with x axis still 13 but you may have to not quite go to 65. You decide but as soon as you start to blow out the core with that white circle I would stop and reduce slightly. The white circle will reduce when you dogleg the curves line so just watch. I think after 4 yrs of learning I'm for the subtle look. Hope this helps.
Thanks so much for the advice. Looking back now I have pushed the image quite a bit and blown out that centre part. I followed your instructions and got the following result which I think is quite pleasing.
Much better Carl. I look at the second image and it looks much more natural rather than the previous. Have a look at the difference between the stars as the latest image has much more realistic stars. I would definately have a read of Rod Wodaski's "The New Astro Zone System for Astro Imaging" and there is a guy here who has done some movies about processing which I have found very helpfull as well as Google Utube Astronomy Imaging Processing and have a search. Keep them coming.
OK, here is the image i did before just cropped to 1080 high in original resolution from the camera. Lets me do better quality jpg so less noise added and removes the bent stars to the right of the image.
I use the 450D, and I recommend doing 4 or 5 by 5min exposures. On fainter targets if there are no bright stars in shot then go for 10minutes (possibly longer? I have not yet tried with 450D???). It does make a big difference. On objects with great contrast then do both 5 min and 10 min and do HDR or create a gaussian blurred mask of the brighter image and apply the dim image over the bright image using this to bring out over exposed cores (M42 comes to mind).
Doing 2min exposures on a faint target is not real good as the edges of the object are about as bright as the noise of the camera. Once stretched I'm seeing a lot of red/blue blotchy pixelation between the stars, we're stretching out the noise of the camera. Doing lots of exposures is great if you have high initial brightness of the target being captured. Exposures are not added together as they are stacked. What the software is doing is comparing them to remove the noise hence increasing the contrast of the brighter target and letting you stretch the image more without showing up more noise and grain.
Don't waste too much time at first doing 20 shots. Try for 5 or so longer shots. More is better, but not if you have limited time. Spend more time polar aligning and setting up. If your stars are not round at 2min, then they will be worse at 5min.
Allow for dark, bias and flat capture time. I noted you mentioned nothing about bias shots. They are important to remove readout noise from the darks and flats and images. Again, just run 5 of these at first. You can use darks and bias from previous nights work if you forget to take them. I run them with the cap on the camera body whilst I pack up the scope so they are taken at the same temperature as the main images.
Your image without flats caused the center to go bright. Without a lightbox this can be removed pretty well with software and is important to do, especially with this round target near the center. When you push to 10min exposures on faint objects you will bring out the dust donuts on the camera sensor, so a light box is better.
The details you've provided are an excellent help. 
