One of the real trouble jobs in #astronomy is collimating a reflector telescope. In particular, Maksutov-Cassegrains, like the ETX90, are tricky.

Fortunately, Escher over Cloudy Nights has posted a really useful guide.

https://www.cloudynights.com/topic/391392-dont-mess-with-etx-collimation/

How good is my camera lens?

This is a series of images of an artificial star as seen by a camera lens and digital camera. They range from one side of best focus, through focus, and onto the other side of focus.

I see two errors:

1. Collimation/alignment

2. Astigmatism (probably pinched optics...bad optomechanical support)

I will disassemble this lens to investigate further.

https://www.skyatnightmagazine.com/advice/how-to-star-test-a-telescope