Yep :t:I notice that the prisms are reversed. I wonder if that was done to move the center of balance of the SF back closer to the eye cups?
Bob
Okay, so it seems that longer bins give more freedom for design/ different construction choices and are less prone to aberrations, mainly chromatic. Doing a basic calculation I found that the distance between the outer lenses of the Zeiss SF is 31mm larger than on my old 42mm bin. which translates to a 25% larger focal length. This also translates to a 25% smaller entry angle (for the outer light rays into the next lens 90-10 deg= 80 deg and otherwise 90-12,5=77,5 deg). I was thinking about it for a bit last night, and I can imagine that the better entry angle (closer to 90deg) results in less reflection issues.
Thinking along these lines only works for binoculars with simple achromatic doublets for objectives. ..... By the time the objective light cones reach the eyepiece fieldstops (after further massaging by the negative eyepiece field groups) the Swaro might be the one with the longer effective focal length and lower axial aberrations in spite of its shorter physical length.
Also, it's baffling, not "entry angle", that determines freedom from internal reflections.
I certainly do not think image quality of a bin can be judged solely by binocular length, but there must be some advantages to longer tubes and I like to know which benefits these are |:d|
Well, there's an advantage to a higher focal ratio as long as designs and glass types remain identical. You can see that in a star-test when you compare a binocular at full aperture to itself at a stopped down aperture. That's one reason I prefer binoculars with large exit pupils in daylight. The reduction in effective aperture and increase in focal ratio imposed by the eye will nearly always lead to lower aberrations.
400 years maybe.
... but I do have a question: in photography a stopped down diaphragm gives more depth of field. Would/ could that effect also take place in (stopped down) binoculars?
A rather controversial question I suppose, but hey... I am fairly new here, so I can ask stupid and controversial questions.