What size for EL flat panel?

[buzz]

Now I am pier-mounted, I can fix a flat panel to the wall of the obsy, about 150cm distant from the camera.  I use a selection of FLs from 180 f/3.4 camera lens to 2000mm f/8  RCT and from the field of view, projected on the wall, I calculated I only need a 24 cm diagonal to fill the sensor with the tiny lens and only 2.5 cm for the big one! Clearly it will not be in focus, so I will need some margin.

I know that it is often the case that folks rest a panel up against the optics' / dew shield but this is not the case here. If the image of the flat panel fills the sensor - this should be good,.. right?

[cjdawson]

My understanding is that the image from the flat light plane needs to cover the optics in their entirety. Whilst it does make sense that it only needs to completely fill the sensor, I'd advise going the extra step and ensuring that the entire optics are covered.  They way, you are not limited to using camera with a sensor size up to what your panel can cover.

Maybe an idea is to have the panel mounted on a frame that you can take off the wall when you use it, put it on your optics, do the flats, then put it away.   This also has the advantage that you won't need to move the scope just to take a flat, as the panel itself will be the moving thing.

[buzz]

I realised my mistake. I was considering the angular field of view from the POV of the sensor, but, since my panel is close to the optics, I have to add the angle to the aperture diameter. So, in summary the panel always is bigger than the aperture. For my 10" RCT I will likely use an A2 panel from ELWirecraft - which is 23x16".  I knew the prior analysis did not seem right, I just couldn't think why.

[Gina]

I just use a clean white cotton T shirt and daylight for my flats - works well    Well, it used to when I used to do astro imaging and we had the odd clear night sky