# 01 Dec, 2015 06:02
I am imaging from a dob, and so my tracking limits me to a maximum of 1.2 seconds exposure at an unmagnified focal length. When I recently set my sights on some dim DSO targets, I collected a high volume (5000+) frames. DSS works well for between 100-300 frames, giving me some light details if I stretch the histogram, but it seems to fail completely when I try to stack many of the frames simultaneously. The resulting image from 2500 frames does not have the same detail and sharpness that the separate stacks of 100-200 of the exact same data yields.|
Any ideas for how to solve this?
I have tried stacking those stacks of 100-200 together but the resulting image has strange artifacts and does not seem to appreciate reprocessing..
# 01 Dec, 2015 06:33
I am just starting to write some astro software and am interested in tasks that can not be solved currently.
If you like you could send me your raw data (perhaps a DVD or something … and I could do some analysis and try to get the best results for you.
# 02 Dec, 2015 21:48
|I highly recommend Astroart 6 (http://www.msbsoftware.it/astroart/)|
# 04 Dec, 2015 22:50
CCDstack works great in 64 bits for over 1000 images for me and provides great calibration.|
# 07 Dec, 2015 16:36
The OP makes me wonder… How many different stacking algorithms have you tried in DSS?|
I know they have the following "stacking modes", and I'm assuming you've tried all of them, but if not, you may want to try with a different setting than what you originally ran with:
Median Kappa-Sigma clipping
Auto Adaptive Weighted Average (I've had some luck with this one, but nowhere near 5k frames)
Entropy Weighted Average (High Dynamic Range) (I've had some luck with this one too)
Aside from that, have you tried any other stacking or astro-tools? PixInsight is one I could think of, but may take a while… I'm not sure if they have a cap on frame number though, as I have not ran into it yet. It is a 64 bit application, so it has that benefit.
# 07 Dec, 2015 17:08
Thank you all for the repliesreplies! I am currently downloading CCD stack to give it a try, although it is unlikely I will cough up funds in the near future.|
Many of the alternate stacking algorithms in DSS have offered me a ridiculously long "producing final image" with an estimated time in the literally hundreds of hours
My best results have been with 100 frames at Adaptive weighted average or with 400-500 frames at Average
# 23 Dec, 2015 17:35
|Estimated times in DSS are rarely accurate. My stacks often complete in something like 1/5th to 1/10th the estimated time. Not that I've ever done THAT many…|
# 04 Jan, 2016 09:19
In DSS you can first register the images, and then stack them later. This way you should be able to process more frames.|
In the 'Register Settings' screen, uncheck 'stack' to first process the images without stacking them (only registration will happen).
Registered images have all informations displayed in the list: score, angles, etc.
Later you do only the stacking of the already registered images. Unchek 'Register already registered pictures'.
Also, for a large number of frames you should only stack a narrow selection of the best images.
Stacking the best 10% of 5000 images should give you much better results than stacking all the frames, especially if many of the frames are 'less-than-perfect'.
This way you reduce the CPU load for the computer, the processing time, memory usage, etc.
# 19 Jan, 2016 13:44
Try Autostakkert 2 (http://www.autostakkert.com/). Over the years it has mainly be used by planetary imagers (the author - Emil - is also an amateur astronomer/planetary imager) but more recently he has been using it to stack 1000s of short frames from the newly available/very sensitivy CMOS sensors. It may be worth getting in touch with him but he has posted in CN recently with results on DSOs (http://www.cloudynights.com/topic/502370-4-second-exposures-asi174mm-16-dob-m51-and-m57/?hl=zwo#entry6623555) .|
# 22 Nov, 2016 18:54
There are many programs available for doing stacking, a few of which have been mentioned already. Like Martin, when I first started, I tried writing my own image calibration, registration and stacking software. It did work for my specific FITs files, but I quickly realized that my work was terribly outclassed by existing tools. My favorite is PixInsight (there is a free 45 day trial). It covers all of the pre-processing (like stacking) as well as post-processing.|
There is a way you can do this with DSS though. Stack only 200 at a time. Take the 1st 200, stack them, then save the result as a 32-bit TIFF with the processing changes embedded. Then do the next stack, etc. Eventually you will have 25 stacked images. Now take those 25 images and load them into DSS and stack them. It is a little time consuming, but should work.
OrionRider's suggestion of only stacking the best frames is excellent. It reduces the number of frames to stack but you will get more detail in the final result. I don't know that I would drop down to 10% though. At 1.2s you aren't getting much signal and with only 500 frames that would be around 10 minutes of exposure time total. Unless the object is very bright you aren't going to see much. Doing 80% will allow you to toss out the worst offenders but you will still have 1.33 hours of exposure time in the end. In this modified version, you would load 250 frames into DSS at a time and tell it to select the best 80%. That should get you about 200 frames that will actually be stacked. You should end up with 20 stacked files that you can then stack together.
# 22 Nov, 2016 19:19
|Thanks for the help everybody! I was able to figure out my tracking system and increased my exposure length to about 4 seconds. This has reduced my frame-count nicely. I use DSS to remove a significant number of frames based on my preferred FWHM. After DSS I have been using Pixinsight to stack the best quality frames, and to do all of my processing. All the responses are very very appreciated. Clear skies!|
# 22 Nov, 2016 19:49
If you are using PixInsight, is there a reason you aren't using the SubframeSelector script to identify images you want to discard? You can even weight the results using an arbitrary expression to adjust your stacked results (i.e. targeting FWHM over SNR).
# 23 Nov, 2016 15:13
I would like to bring to attention this Photographers work. He uses 12000 X 1 sec images taken with a planetary camera to produce some completely amazing images. He also uses a .8x flattener along with a .7x Focal length reducer at the same time!!! He uses registax i believe to accomplish this. He uses a ASI224MC to do these. He is my imaging hero right now |
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