ceasar said:Sounds (looks?) like a form of blackout (white out here?). Make sure you have your IPD set correctly and your eyecups positioned correctly. When it happens again move the binoculars closer to your eye or further away to see if it disappears. Does it happen if the sun is behind you, in front of you or all the time?
henry link said:Darrell,
Unfortunately you've had the misfortune of noticing an imperfection in the internal baffling design of the FL on your first day out with it. The "half moon" you see at the bottom of the field is actually two half moons superimposed over each other. They are out of focus reflections caused by the relatively bright light of the sky reflecting off the edge of the objective cell (mostly from the spacer between the air spaced elements) and a somewhat brighter second reflection coming from the edge of the focusing element cell. Properly sized knife edged baffles installed at the rear of those cells would have completely eliminated the reflections. You can see these crescent shaped reflections at the edge of the exit pupil if you move your eye back from the eyepiece when you see the "half moons" and look at the edge of the small bright circle formed by the exit pupil.
In the field these reflections are actually seldom visible. It takes a particular set of lighting conditions. It's most likely if you are looking into a dark area on a cloudy day or at twilight with open sky above you. Your eye needs to be open quite wide to catch a reflection from beyond the edge of a 5.2mm exit pupil. In bright sunlight the reflection is likely to fall harmlessly on the iris. If it's any consolation I've owned the 8x42 Fl's for about two years. I've looked through them thousands of times and almost never notice the problem. I consider it a minor annoyance since I know it could have been avoided in the design, but it's really not too bad and far from a deal breaker in a binocular with so many other virtues.
I should add that unbaffled reflections from objective cells are very common in binoculars. If you can see them under some conditions at least you know the objective is relatively unvignetted. Not seeing them isn't necessarily even a good sign. Some binoculars have prisms so undersized that they vignette the edge of the exit pupil. That takes care of the reflection problem but also effectively reduces the aperture of the objective.
henry link said:Thanks for all the nice stars, Bob. I'm almost speechless.;-)
I played around with this a little more today. I set up a tripod near a window and mounted various binoculars on it. I pointed the binoculars down toward a dark floor beneath the window and observed the reflection from the objective edge directly through the eyepiece and by looking into the binocular innards with a magnifier through the eyepiece.
Nearly every binocular I tried showed a "half moon" across the bottom of the field, some brighter than others. In looking directly through the binoculars large exit pupils have the advantage since the reflection is at the edge of a larger circle and therefore less likely to enter the eye. Some binoculars were much worse than the Zeiss FL. The absolute worst was a Steiner 6x30 which has a smooth highly reflective tube between the objective and the prism (what were they thinking?). The best performers in the test were the Nikon 8x30 EII and its predecessor E models which all use the same objective cell design. The big secret in these binoculars is a 5 cent piece of thin stamped metal formed into a shallow cone about 5mm deep and attached to the rear of the objective cell. It's sized and shaped to do a pretty good job of masking off the reflection of the cell edge. There is no baffling at all between the objective cell and the prism shelf in these binoculars. The interior is just painted flat black. In contrast the 8x32 SE has an impressive looking baffled tube between the objective and the prism. This should help generally with light scatter and improve contrast, but it doesn't do as much to mask the objective edge, so the SE didn't do quite as well in this test as the E and EII. For this particular problem elaborate interior baffling is not the solution. Just one properly designed and placed baffle is all that's needed.
ksbird/foxranch said:....There might have been a very few additional warranty problems with the Nikon EII binocular "internal cones" coming loose and so for some reason Nikon stopped using these cones.....
Somewhere in another website (I believe it was in another galaxy, long, long ago.) I read that man's object to achieve perfection in binocular construction was ultimately doomed to failure because of the inherent difficulty in coordinating the passage of light rays simultaneously through four sets of lenses and and a various variety of prisms through two OTA's at the given focal lengths of F4 into two differing eyes.
Binoculars are like quoits. Closeness counts!