Size of Eyepiece Lenses vs. Image Performance (1 Viewer)

jremmons · Jan 2, 2019

Morning all and Happy New Year,

I've noticed the current trend in a lot of the upper-level optics is to have very large eye-piece/ocular lenses. Do such large lenses in any way improve the quality or 'ease' of view? If so, how/why? I don't know much of the technical design aspects of binoculars, though I have learned a lot from this forum particularly regarding distortions and aberrations, but these are certainly one of the most important tools of the trade, so to speak.

Thanks,
Justin

henry link · Jan 2, 2019

The diameter of the eyelens is determined by two things: the apparent FOV and the eye relief. The eyelens needs to be wide enough for rays from its edges to meet at a point equal to the eye relief distance behind the eyepiece thus forming an angle equal to the AFOV. In modern binoculars with large eyelenses that's likely to mean long eye relief combined with a moderately wide AFOV. No prediction can be made about the "ease" of view from the eyelens size.

jremmons · Jan 2, 2019

Thank you very much for the explanation Henry; this is the exact kind of information I was interested in. I suppose this is why some of the newer models, such as the Zeiss SF, are particularly pleasing to me as I need long eye-relief and desire a wide FOV to consider a view particularly "easy".

I suppose this is why you mean "ease" is not predictable from eye-lens size, as not everyone has these same requirements to produce an "easy" view.

ceasar · Jan 2, 2019

jremmons said:
Morning all and Happy New Year,

I've noticed the current trend in a lot of the upper-level optics is to have very large eye-piece/ocular lenses. Do such large lenses in any way improve the quality or 'ease' of view? If so, how/why? I don't know much of the technical design aspects of binoculars, though I have learned a lot from this forum particularly regarding distortions and aberrations, but these are certainly one of the most important tools of the trade, so to speak.

Thanks,
Justin

And likewise Justin;

A Happy New Year to all!

I have noticed on my Nikon 10x32 EDG that the diameter of the eyepiece lenses are wider by a couple of millimeters than the diameter of the eye piece lenses that are on my old Nikon 10x32 LX L which it replaced.

At the same time the new EDG received larger, wider and more comfortable replaceable eye cups while the eye relief increased from 16mm to 17.3 mm. The FOV remained unchanged at 6.5º from the older LX L and the close focusing distance of 2.5m remained unchanged. The EDG also got new di-electric prisms.

All this I think also contributed to the "quality" or "ease" of view I am sure; although the older 10x32 LX L still is an excellent binocular.

Cordially,

Bob

Vespobuteo · Jan 2, 2019

Probably not a coincidence that Swaro SV, Zeiss SF and Leica Noctivid all have larger ocular lens diameter than most.
Even the "cheapo" Zeiss Conquest HD have pretty large ocular lenses.
It's the evolution of optics.

dries1 · Jan 2, 2019

I think Henry is right speaking about the increased ER, if you look at many inexpensive and moderately priced models, eye piece diameter has increased in size equaling premium glass such as SF, SV or NV. ER has increased in models 7 through 10X as compared to 10 - 20 years ago, a demand for use with eyeglasses.

Andy W.

james holdsworth · Jan 2, 2019

The Victory FL models have relatively small ocular lens but I have found many models to be very easy to use, supplying more than adequate eye-relief.

Alexis Powell · Jan 2, 2019

henry link said:
The diameter of the eyelens is determined by two things: the apparent FOV and the eye relief. The eyelens needs to be wide enough for rays from its edges to meet at a point equal to the eye relief distance behind the eyepiece thus forming an angle equal to the AFOV. In modern binoculars with large eyelenses that's likely to mean long eye relief combined with a moderately wide AFOV. No prediction can be made about the "ease" of view from the eyelens size.

I feel like there must be more to the story, or at least more that is worth explaining. Why do oculars of bins with fairly similar specs have such seemingly different diameter ocular lenses? I guess a small difference in eye relief or FOV or both must translate to a large difference in ocular lens diameter. The Zeiss 8x32 FL was a leader for FOV (420 ft at 1000 yards) and claimed eye-relief (16 mm) in x32 bins when it was first released, but its ocular lenses seem tiny in comparison to recent models. If memory serves, the oculars of the 8x32 FL are smaller in diameter than the oculars of the 8x25 Victory Pocket, which has very slightly longer claimed eye relief (16.5 mm) but a smaller FOV (390 ft). The oculars of the Swarovski 8.5x42 EL SV seem enormous compared to the original EL, which had only modestly less FOV and eye-relief.

--AP

Binastro · Jan 3, 2019

It is also due to the focal length of the eyepiece.
In a fast system the eyepiece focal length will be smaller, for say an 8x instrument, than a slower system.
So the lens elements can be smaller.

Some 1940s military eyepieces were huge, probably too big for a binocular.

ceasar · Jan 4, 2019

james holdsworth said:
The Victory FL models have relatively small ocular lens but I have found many models to be very easy to use, supplying more than adequate eye-relief.

There was a discussion here recently about the eyepiece used on the 7x42 Victory FL binocular. It seems it uses the same eyepiece that is on the 8x42 Victory FL which is smaller than an eyepiece used on typical 7x42s.

If my memory is correct, to get the power of the binocular down to 7x the objective tubes were shortened to give the binocular a shorter focal length than f4.

Bob

henry link · Jan 4, 2019

Alexis Powell said:
I feel like there must be more to the story, or at least more that is worth explaining. Why do oculars of bins with fairly similar specs have such seemingly different diameter ocular lenses? I guess a small difference in eye relief or FOV or both must translate to a large difference in ocular lens diameter. The Zeiss 8x32 FL was a leader for FOV (420 ft at 1000 yards) and claimed eye-relief (16 mm) in x32 bins when it was first released, but its ocular lenses seem tiny in comparison to recent models. If memory serves, the oculars of the 8x32 FL are smaller in diameter than the oculars of the 8x25 Victory Pocket, which has very slightly longer claimed eye relief (16.5 mm) but a smaller FOV (390 ft). The oculars of the Swarovski 8.5x42 EL SV seem enormous compared to the original EL, which had only modestly less FOV and eye-relief.

--AP

Believe it or not I don't think there is more to the story provided all three parameters are accurately measured. If something seems off for a particular binocular after measuring the eyelens it's almost certainly because the published specs for eye relief and/or AFOV are off in some way. Either the eye relief spec is just inaccurate or perhaps is measured from the eyecup rim or from the center of a concave eyelens and/or the AFOV is fictitious or calculated (by either the ISO method or simply multiplying magnification by real field) rather than measured to include distortion.

Henry

Size of Eyepiece Lenses vs. Image Performance (1 Viewer)

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