[JohnH]

Never thought of that - I wonder if it is gradient free enough though, they are lit from the edges, having said that, the section of screen observed would be small....maybe the gradient would be insignificant.

I would think you need to leave the OTA focus alone too, that might help blurr out any gradient - better make sure there are no fingerprints on the screen too...

Any experts out there care to comment - if this is a reasonable approach I can see adding flats to the end of an imaging session father than relying on stock shots taken with the same imaging train...