Thanks for the comments folks. It will take some time to get on top of everything I need to know to get the best out of this system.
You are correct Peter I was just trying to see what this system would do.
Greg you have nailed it the left side of the image plane is closer than the right side of the image plane to the incident light. This of course means the detector is physically the reverse as the image is inverted to the object.
When I get a chance I will do a series of exposures and change the focus by a set amount between them. I have already seen the effect of moving focus out. The LHS corners are eggy and the RHS is fine. By moving out by 800 steps of the Atlas focuser the LHS is then good and the RHS takes on the appearance of the LHS previously. This is about 80 micron! This gives me a ball park figure for adjusting the rear plate of the RH200.
Below are a couple of way out of focus images 20k steps apart of the Atlas focuser. You can see how a slightly out of focus star can produce an ellipse due to the inherent vignetting that is inevitably present in any wide field optic.
I do not want to start adjusting the optic until I am sure of all the facts.
The images so far though indicate that this large sensor will work satisfactorily with the RH200 for widefields and mosaics. The corners will never be as good as the centre but what optic is at F3. When we can make a concave spherical CCD we can then ignore field curvature! Remember curved film in Schmidt cameras.
Thanks for any advice again as it is good to get confirmation or otherwise on my ideas. The weather is the main thing stopping progress but it gives me more time to think things through thoroughly.
At position zero 4MB
20k steps further back 4MB
From the shape of the out of focus stars you can get a visual idea of the amount of vignetting. The factory set collimation also looks OK.