Flat Field Exposure Times

[Mav359]

Hi

How do i work out how long i need to expose for to get optimal flats??? I know about leaving the Focus & Camera orientation the same.

I'm using a flat field panel over a C9.25 Hyperstar with a QHY8L. I can use Nebulosity or EZCAP that came with the camera for the stats on the frame i'm just not sure how to work out how long i need to expose for.

Cheers

[ollypenrice]

It ain't going to be long in a Hyperstar! You're also going to have to be careful not to create local shadowing artefacts and reflections as the panel illuminates the camera on the front of the system, and maybe the cables. I'm not sure how you'll be able to use a panel with this rig. I must say that I'd be more inclined to try sky or observatory flats, but I'm only guessing since I've never tried a Hyperstar. The panel may work fine but just remember it is going to be pouring light onto the camera body.

The exposures should take the peak of the histogram about a third of the way over to the right. I go for about 18000 counts on my CCD cameras. You can do this by choosing an appropriate exposure time and/or by filtering the light source through a screen. (Typing paper, etc.) I suspect that, at F2, you'll need to do that. Cameras with mechanical shutters must have light sources dim enough to give exposures of at least a few seconds or the wipe of the shutter will put a gradient on the flats.

Olly

[teleskopjo]

Yes this is interesting, how can you use a flat field panel over a HyperStar unit?