[Roo]

Hi,
I'm a newbie to this forum and planning to build a Newtonian reflecting telescope (Dobsonian).
I'm interested in the ultra wide eyepieces available that have apparent fields of view around 82 degrees. I have read that sometimes they can be limited by the telescope internal geometry. Can someone tell me what the limitations might be and how to calculate them for a Dob?
Cheers,
Andrew.