Optimum number of flats?

[iantaylor2uk]

I only usually take 10 flats/10 darks/10 dark flats for calibration but I often see people on here take 50 or more flats. Is there any benefit to taking more flats, and is there an optimum number?

[CloudMagnet]

Its worth doing more, but becomes diminishing returns. I take 25 each of darks and flats and never really had a problem with them not properly correcting in the stacked image. I suppose you would see an improvement doing 50+ but I suspect that the gains would be marginal and you would see much bigger benefits elsewhere like dithering more often, lower camera temperature etc...

[Budgie1]

I tend to air on the side of safety and do 20 of each type of calibration frame. But as long as the calibration frames are correcting what you want them to correct and to the quality you're happy with, then that's fine.

The DeepSkyStacker FAQ about calibration frames says 10-20 of each should be enough.

[Dazzyt66]

Here's an excellent explanation of taking calibration frames and the reasons why (and indeed the diminishing returns of doing loads). I don't use darks at all but go for 30 bias and flats.

https://youtu.be/JKWmP5W3nts

[michael.h.f.wilkinson]

Taking lots of flats or bias frames does not as a rule take much time, so I typically create 50 each, reducing the noise levels by a factor of about 7. That is adequate, I find. Less would probably work. Darks take quite a bit longer to acquire, due to the long exposure times. However, with fixed-point cooling, I can take darks whenever I like, so I just let the camera take 50 of them as well. Previously I used 30, and that also works well.

[vlaiv]

I'm in - "if it's not too much hassle then do it" camp and take x256 flats, x256 flat darks and at least x64 darks but often more - as those tend to be cumulative and you can add more if it's cloudy and you want to see if your darks changed significantly from those that you already have (which you do by just creating another master from new session and subtract from old master - if you get pure noise with average pixel value of 0 - you are fine).

My flats are very short - like 10ms range and it takes longer to download frame then to expose it (although I have CMOS cameras) as I have very strong flat panel. I never had issues that people experience with flats due to short exposure.