I have an Explore Scientific AR102 refractor. I have successfully taken photos by attaching my Nikon DSLR to the Crayford focuser. But then I can’t look at the rear screen of the camera to check/adjust setting nor to view the previous exposure.
So, I thought that I could attach the camera to the diagonal. I did a daytime terrestrial test. Here’s what I found.
With a 20mm EP attached to the diagonal, the scope focuses on an object 1 mile away at Crayford=15mm and 88mm for an object 30 feet away. When I swap the EP for the camera, the near object comes into focus at Crayford=55mm, but I can’t focus on the distant object.
Does this mean I need Crayford = -18mm (e.g. the focuser would need to go past 0 and retreat into the OTA)? Is there some lens that I can put into the optical path to give me -18mm of negative focus?
Thanks for any explanation or suggestions.