Jorgen,JH wrote:I use a microscope. The distance between the microscope lens and the tube lens I fixed. The distance between the tube lens and the sensor is set so the tube lens is focused at infinity (in this case a three top at my neighbours). I focus the microscope on the butterfly scale and take a picture – the second picture in the first row in the series above.
If I increase the distance between the tube lens and the sensor the lens focus closer. If I decrease the distance the lens focus further away. When I did this the picture was totally out of focus and I needed to refocus the microscope before I could take a new picture.
My point was that a few mm wrong in tube length (deviation from infinity) at NA 0.6 could be OK at least in the center of the picture.
[Edit: I am sorry, I should have mentioned in the beginning that the 150mm apo gerogon lens that I used cannot focus by itself, it needs to be used on bellows or tubes]
Best regards
Jörgen Hellberg
Thank you for doing this, the completely confirms what I had thought.
Best,
Mike