Black out effect when talking about telescope eyepieces?

Question

Was looking at reviews of different eyepieces and the term "blackout effect" came up, even in the review of the 12mm Nagler type 4 and I was wondering what the blackout effect was

Answer 1

Some eyepieces are sensitive to eye position such that placing your eye too close will cause the image to black out. This is mostly a problem with long eye-relief eyepieces. There is also the "kidney bean" effect, in which parts of the field black out. This typically happens over roughly bean-shaped areas, hence the name. Kidney-beaning is worse in the daytime when your pupil is smaller.

Answer 2

I believe this refers to what seems to happen when a person's pupil gets misaligned with the image circle coming out of the eyepiece. I've experienced it many times. Better eyepieces have a much larger image circle so the eye is much less likely to get outside that circle.

Answer 3

I agree with injanier's answer, but I thought the blackout effect was associated with wide field of view rather than long eye relief?

Answer 4

particular, a Barlow lens will double the magnification of any eyepiece so 10mm + 2x barlow will supply the equivalent of a 5mm eyepiece. simply by fact which you have already got a 20mm eyepiece you may desire a 2.5x or a million.8x barlow, so as which you at the instant are not duplicating the 10mm with the 20mm. do exactly not purchase the very maximum inexpensive barlows nevertheless, they're going to degrade the overall performance of the eyepieces.