I have read that kidney beaning occurs as a result of spherical aberration in the exit pupil, especially with regard to wide field eyepieces.
I got my UO HD 18mm today and observed my neighbor's doorbell and saw no kidney beaning.
When I put in the Nagler 17mm T4, that's practically all I could see. The more I tried to find a place where I didn't see it, the more I couldn't. I noticed that to get away from kidney beaning entirely I had to back out so far that it no longer was a wide field eyepiece. Even as I got to "a good spot" I noticed that there was a very slight depression or darkness in the center of the fov that you had to sit real still to notice. It occurred to me that when some people do reviews and talk about "light pass through," they may in fact be talking about marginal kidney beaning that has caused some darkness in teh fov but not enough for them to move their heads and correct.
The XW20 did the best job on the doorbell (this is in the FS128). I could get kidney beaning but I had to really work at it by screwing down the eyecup.
XW14 was a bit more jittery. What I noticed here that surprised me was that when I got a kidney beaning effect it started *from the outside in.* In the 17 NT4, on the other hand, I could get the effect, and often did, from the center out.
I guess with nighttime observing kidney bean won't be as bad because a wider pupil can accommodate more curvature in the exit pupil of the eyepiece? I don't know....
But I did see enough "marginal effects" today that I began to think that the issues of "clarity and transmission" that many of us report with regard to XWs may have more to do with the way the kidney bean is controlled.
regards
Greg N
I got my UO HD 18mm today and observed my neighbor's doorbell and saw no kidney beaning.
When I put in the Nagler 17mm T4, that's practically all I could see. The more I tried to find a place where I didn't see it, the more I couldn't. I noticed that to get away from kidney beaning entirely I had to back out so far that it no longer was a wide field eyepiece. Even as I got to "a good spot" I noticed that there was a very slight depression or darkness in the center of the fov that you had to sit real still to notice. It occurred to me that when some people do reviews and talk about "light pass through," they may in fact be talking about marginal kidney beaning that has caused some darkness in teh fov but not enough for them to move their heads and correct.
The XW20 did the best job on the doorbell (this is in the FS128). I could get kidney beaning but I had to really work at it by screwing down the eyecup.
XW14 was a bit more jittery. What I noticed here that surprised me was that when I got a kidney beaning effect it started *from the outside in.* In the 17 NT4, on the other hand, I could get the effect, and often did, from the center out.
I guess with nighttime observing kidney bean won't be as bad because a wider pupil can accommodate more curvature in the exit pupil of the eyepiece? I don't know....
But I did see enough "marginal effects" today that I began to think that the issues of "clarity and transmission" that many of us report with regard to XWs may have more to do with the way the kidney bean is controlled.
regards
Greg N
"Scope will get you through times of no money better than money will get you through times of no scope." --Freewheelin' Franklin
