When I built optical instruments in the past I got into the habit of a quick proof of principle before exploring the full capabilities. I find it useful as a test of understanding - to really make sure you know what you are doing before going to any further effort. So it was with the moon camera.
I live on the side of a valley and on the opposite face is an old factory chimney, around 600m away. Often used as a convenient test object for my camera systems it was once again put to good use. If my calculations were right and I placed my D750 around 4m from the mirror with the 200mm lens focussed at around 2.1m I should get a reasonable image in the mirror.
Pre-flight check completed. Time to open the throttle and see if it works full scale. Watch this space...
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I would expect the image of the distant chimney to be 2m from the mirror but highly magnified. To make this easier to capture I used a 200mm lens to produce a minified image onto the sensor, and a much improved depth of focus. The image scale should be roughly what I would see imaging the chimney directly with the D750 / 200mm lens combination. This proved to be the case.
I set the lens to f/8 again to throw the mirror mount somewhat out of focus. It also reduced that veiling glare - I still need to clean that mirror!