Are 20 frames like this suitable for flats?
Taken at iso1250 with my iPad as a light source. No t-shirt around the end of the scope.
Thanks JT
Thanks James I won't be able to get this to 1 to 2 seconds from the current shutter speed and iso. Putting the t-shirt method on would enable me to lengthen it some but... I have no white t-shirts.Baskevo wrote: ↑Sat Jan 04, 2020 8:00 am They say your histogram should be between 1/3 and 1/2 of the histogram. People can get really picky and say it has to be 51% of the histogram. The only thing you can do is try it, and see what works, unless you want to get technical, which works just as well.
I take 50 flats because there's so much debate about the right now, I figured I would rather spend the little bit of extra time taking the extra frames, and then I have the option to stack more if I want
People also recommend shooting at least 1 to 2 seconds for flats, to avoid the shutter darkening the frames. but again, just try it and see if it works, and if it doesn't, try increasing the histogram to 50% and the exposure time to above 1 second. If that doesn't work, then you can try getting technical and going through this website, which helped me a ton (along with @Stuart)
https://www.myastroscience.com/proper-flats-with-dslr
Fair enough…Baskevo wrote: ↑Sat Jan 04, 2020 3:24 pm Dark frames are not the same as dark flats. Dark flats are similar to bias, mostly used for CMOS and CCD cameras. They are used instead of bias because some cameras don't work well with bias I think.
Why such long exposure lengths? You are going the opposite direction lol you should try to get the calibration frames and other basics down before moving on to 5 minute exposures... I've seen really amazing images with 30 second stacked images, but those only come with calibration frames. Without calibration frames, it doesn't matter if you have 10 second or 5 minute exposures, your images will be plagued with noise, dust motes, and vignetting.
A lot of people argue that it's actually better to take 500 30 second exposures rather than so many 5 minute exposures because you lose less frames (losing 1 frame from a satellite is worse in a 5 minute exposure than 30 sec). I have found that the difference between 120 stacked 30 second exposures and 12 stacked 5 minute exposures is minuscule, and you can get just as much detail! I'm sure some will disagree, but I don't think anyone will disagree that you should make sure you have calibration frames down before you push your exposure length
Sorry I didn't mean for that to sound rude, my tone was more "that's impressive!" than "you're doing it wrong" when I typed that you are doing it backwards lol of course you can do it however you want! Whatever works for you man! I'm just saying that I think you would get a lot more out of your images with calibration frames than trying to max out your guiding so farmactech wrote: ↑Sat Jan 04, 2020 3:40 pmFair enough…Baskevo wrote: ↑Sat Jan 04, 2020 3:24 pm Dark frames are not the same as dark flats. Dark flats are similar to bias, mostly used for CMOS and CCD cameras. They are used instead of bias because some cameras don't work well with bias I think.
Why such long exposure lengths? You are going the opposite direction lol you should try to get the calibration frames and other basics down before moving on to 5 minute exposures... I've seen really amazing images with 30 second stacked images, but those only come with calibration frames. Without calibration frames, it doesn't matter if you have 10 second or 5 minute exposures, your images will be plagued with noise, dust motes, and vignetting.
A lot of people argue that it's actually better to take 500 30 second exposures rather than so many 5 minute exposures because you lose less frames (losing 1 frame from a satellite is worse in a 5 minute exposure than 30 sec). I have found that the difference between 120 stacked 30 second exposures and 12 stacked 5 minute exposures is minuscule, and you can get just as much detail! I'm sure some will disagree, but I don't think anyone will disagree that you should make sure you have calibration frames down before you push your exposure length
I agree that calibration frames are very important as is good guiding. However, I don't see it as going in the opposite direction, as you say. I want to be able to achieve both. If there are star trails, no amount of good darks, flats or bias will fix it. I see many images where they are exposing for longer than 5 minutes and wanted to be able to achieve it with my equipment, not that the majority of exposures will be that long. With the light pollution I have, 5 minutes is never going to happen here.
Three nights ago I did the 20 - 60 second exposures and compared them to 7 - 180 second ones and while not equal in total integration, the noise was less in the later and the final image was better.
No worries, and I get what you're saying and agree.Baskevo wrote: ↑Sat Jan 04, 2020 10:31 pm
Sorry I didn't mean for that to sound rude, my tone was more "that's impressive!" than "you're doing it wrong" when I typed that you are doing it backwards lol of course you can do it however you want! Whatever works for you man! I'm just saying that I think you would get a lot more out of your images with calibration frames than trying to max out your guiding so far
There are many variables that go into what makes an image look better from night to night. It could be better seeing, it could be more integration time, etc. Of course the longer exposure on each image the better your Signal-to-noise ratio, but you reach a point where you have diminishing marginal return, was my point... I don't shoot over 120 seconds except with narrowband because I live in such heavy light pollution! but even if I didn't, I probably would want more frames than longer exposed subframes, because then I could probably have a longer integration time with more images
I still think that calibration frames are a lot more important than good guiding though, because technically you don't need good guiding to get really great images You will see a difference from 30 to 60 sec, from 60 to 120, from 120 to 180, and so on... but the higher you go the SNR doesn't get that much better, if I understand it correctly. Someone can correct me here if I'm wrong
+1
Spinning my wheels trying to get advice?
thanks James...Baskevo wrote: ↑Sun Jan 05, 2020 12:48 am+1
The best thing you can do is try it
Because of my light pollution, I never shot above 800 ISO, so you should be fine there!
Let us know how your new flats work, and just remember to take them after the imaging session, before moving the camera, change the framing, or anything. This is to make sure that the dust motes and vignetting are in the exact same position on your flats as on your lights.
Good luck!
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