Re: 5" "apo" refractor

Easiest would be a star test and then perhaps followed by letting Jupiter drift from one side to the other of the FOV so you can judge whether the image is good edge to edge. A good EP is required as well as removing the diagonal to make sure it does not effect the tests.

Hi Bill,
The Moon would also do nicely. Off color will show on the limb and edges of the craters if there is any. Plus you can use the Moon to drift it and look at the details over the surface as it moves.