BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="Binastro" data-source="post: 3569284" data-attributes="member: 111403">Thanks Ron.Does the Nikon 8x20 XL have a distortion free eyepiece?I am not sure if your photo shows slight barrel distortion or no distortion.The problem in real life is that I think people measure the field at much closer distances than 1000 yds or 1000 metres, where the field size differs slightly.Also hand held I find that the field is slightly larger than tripod mounted because of slight movement and eye memory.And the IPD makes a difference if not set perfectly. Plus eye positioning.My problem is that I think in angles whereas birders may think linearly.Yet the AFOV even for birders is in degrees, which doesn't seem consistent.And how does one describe a 180 degree field in feet at 1000 yds or metres at 1000 metres?Is it infinite, or maybe not, as space is curved.My professional telescope making friend used a collimator and pinholes at about 15m representing close double star to test his telescopes. And also to examine the star images in and out of focus.</blockquote>