[alfredbird]

I am a little bit confused now.

Wiki says NGC 5139 is about 36.3 arc sec, why it occupys more than 50% of my EP which should have FOV of 42 arc min.

EP 13mm, 65 FOV on a 1200mm F/4.7 10 inch dob, which gives FOV of 0.7 degree.


anyone can help me this those calculation? many thanks.