Maximum magnitude for variable star for a given scope and camera

[Guest]

Last night I did some experiments on exposure times.  I wanted to get an idea of the maximum exposure time without saturating the pixels. My scope is a 200mm SW newtonian and I'm using a canon eos 450d. I found with a star of magnitude 8.060 that the star image became saturated at about 8 to 10 seconds at iso200. I think they recommend an exposure time of at least 15 seconds so on that basis there would be no point with my setup testing a star with a magnitude less than say 9.   It hadn't occurred to me before that there might be such a limit. The picture was sharply focussed so I can probably extend that a bit.

Steve

 

[andrew s]

You can defocus the stars to reduce saturation. It can also improve the s/n ratio.

Have a look here https://www.aavso.org/dslr-camera-photometry-guide

Regards Andrew 

[AlexK]

You want stacking. 8m is a nonsense with the 200mm. I'm getting stars down to 9.5m with the 1.2mm (!) smartphone aperture at 10 seconds (10-12) shots stacked:

http://fo.kukarin.com/storage/originals/83/f9/m97crop.jpg

 

Edited January 26, 2021 by AlexK

[Guest]

That was the purpose of the exercise really - to find out what my parameters are with my setup.