I have obtained an old telephoto lens that was adapted for astrophotography by the previous owner.
I have found a focal plane and I have placed a small webcam (without optics) there. There was a bit blurred and dark image.
Later I have found that the full image is like 2'' large, while my webcam sensor size is way smaller.
Is there a simple and cheap way to make the final image smaller to fit into 5mm x 5mm sensor? Cheaper than to buy a new astrophotography webcam?
When looking for answers I found How to make the projected image smaller by adding one ore more lenses in front of the built in projector lense? , which warns about achromatic troubles.