Wide AFOV bins question

[pipnina]

I have measured the exit pupil of my 10x50s and it has come out as 5mm (pretty much exactly) On my last TFOV test on cassiopeia it came out as around 7-7.5 degrees which still isn't the binoculars stated 8 but is close. (I need to redo the test though since I realised an issue with my method that may have made the value smaller than it is in reality)

The only other way that FOV could have been achieved with the exit pupil correct but without the AFOV being high is by stopping down the front aperture, how would I know if that's happened?

However, I have done some searching and most 10x50s don't go above 6.5 degrees, and I'm yet to find one that advertises 7 or more degrees of TFOV. Why is it so hard to make bins with high AFOV? We've got scope eyepieces that go as high as 82 degrees or even 110 or 120 degrees AFOV. Why do binoculars lag so far behind at around 65 degrees?

    ~pip

[Peter Drew]

My Opticron Elite 10x50 have an Actual Field Of View (AFOV) of 7 degrees due to their apparent FOV of 70 degrees. I believe the Zeiss 10x50w binocular is similar.

It would be difficult to exceed this specification due to the relatively small dimensions of the normal binocular mechanical components. I have a Gernan ww2 binocular with a 8 degree AFOV, 80mm objectives, 80 degree eyepieces and 10x magnification. 

[pipnina]

My Opticron Elite 10x50 have an Actual Field Of View (AFOV) of 7 degrees due to their apparent FOV of 70 degrees. I believe the Zeiss 10x50w binocular is similar.

It would be difficult to exceed this specification due to the relatively small dimensions of the normal binocular mechanical components. I have a Gernan ww2 binocular with a 8 degree AFOV, 80mm objectives, 80 degree eyepieces and 10x magnification. 

Is it the prism size that limits AFOV? That's all I could think of unless the aperture also limits AFOV?

It's my great grandad's bins I'm trying to test- proably made a bit later than your german ones (I think he got them in the early 60s)  I believe made in Japan. Still haven't been able to track down much about the company who made them "Perl" aside from that they were bought by another company (french?) and were in Japan (or was it the other way around?).

[Stu]

Given the similar focal length and magnification, the difference must come from the apparent field of view of the eyepieces, or their field stops? I would think that it is difficult to package eyepieces with more than 65 degree afov in binoculars whilst still ensuring sufficient adjustment in inter pupil distance, not to mention cost.

[Peter Drew]

All these things as mentioned play a part.  

[F15Rules]

Perl was a brand name (not a manufacturer) used for goods sold in France. Perl branded scopes and binos were usually made in Japan and of good quality. For example I had a really nice 60s 60mm F6.6 refractor branded Perl but which also carried the SYW mark denoting that it was made by Yamamoto of Japan who made some of the best achromats in the world in the 1950s to 1970s..I believe they were eventually acquired by Takahashi. Enough said! Some Vixen scopes also carried the Perl name.

Your Perl bins should perform well if they have not been abused..the main deficiency will be light transmission as they simply didn't have access then to the high quality multi coatings now available.

Dave