Ocular Lens Size (1 Viewer)

[oldtimer88]

While this topic has been discussed across BF and CN, after a brief search I wasn’t able to find a clear answer to my question re ocular lens size. I am hoping members will be able to confirm my current understanding or correct me.

A larger diameter ocular lens will have a more forgiving eye box and longer eye relief.

Is this a fair assumption?

Why is this spec reported?

Thank you

 

[henry link]

A larger diameter ocular lens will have a more forgiving eye box and longer eye relief.


Is this a fair assumption?

Why is this spec reported?

Thank you

No, I'm afraid that's not a fair assumption. See the post below.

The Zeiss SFL 8x30 compared with select current 8x30/8x32 roof binoculars

Size and weight ; the retro more equal to a 8x30. According to B&H: SFL 8x30: 459g Leica 7x35: 590g SFL 8x40: 641g So the 7x35 are much closer to the 8x40. Length is: SFL 8x30: 11.9cm Leica 7x35: 13.2cm SFL 8x40: 14.5cm So the 7x35 are exactly in the middle.

www.birdforum.net

 

[oldtimer88]

Not sure I follow. Ocular diameter is a physical characteristic but AFOV is a result of physical attributes no?

No, I'm afraid that's not a fair assumption. See the post below.

The Zeiss SFL 8x30 compared with select current 8x30/8x32 roof binoculars

Size and weight ; the retro more equal to a 8x30. According to B&H: SFL 8x30: 459g Leica 7x35: 590g SFL 8x40: 641g So the 7x35 are much closer to the 8x40. Length is: SFL 8x30: 11.9cm Leica 7x35: 13.2cm SFL 8x40: 14.5cm So the 7x35 are exactly in the middle.

www.birdforum.net

 

[henry link]

In order to calculate the length of the eye relief you have to know BOTH the ocular diameter and the angle of the AFOV of the light cone that emerges from the eyepiece. No prediction can be made about the eye relief if only the ocular diameter is known.

 

[Foss]

Great conversation. Eye relief aside, does a larger ocular diameter help deliver a more forgiving eyebox? I tend to make that association having used 7x42, 6x42, 7x50, and 8x60...the later three, vintage Porros. Thanks

 

[oldtimer88]

Eye relief isn’t what i am concerned with primarily focused on the comfort and forgiveness. Unless eye relief and eye box forgiveness are directly correlated. I guess I am just trying to figure out if what I seem to be experiencing with 8x30s and smaller pocket binos is a result of the smaller ocular lens making that sweet spot tougher to achieve. The ELs and NLs have a big ocular lens so do the SFLs and they are comfortable and easy to get behind without any blackouts

 

[Maljunulo]

My guess (emphasize guess) is that it’s the small exit pupil, which has no correlation with the ocular lens size.

 

[tenex]

Eye relief isn’t what i am concerned with primarily focused on the comfort and forgiveness. Unless eye relief and eye box forgiveness are directly correlated. I guess I am just trying to figure out if what I seem to be experiencing with 8x30s and smaller pocket binos is a result of the smaller ocular lens making that sweet spot tougher to achieve. The ELs and NLs have a big ocular lens so do the SFLs and they are comfortable and easy to get behind without any blackouts

Various difficulties occur in eyepiece positioning, which some individuals seem to have more trouble with than others, but it's not just a function of lens diameter. Pocket bins can be tricky due to unergonomically small eyecups (if you don't wear glasses) and an especially small exit pupil, requiring precise hinge adjustment and careful holding. Another sort of blackout is caused by being too close to the lens, often because of too short an eyecup, but sometimes an unforgiving eye box makes the proper position too finicky to achieve or maintain. (Some find NLs and SFs problematic, although you seem not to.)

 

[oldtimer88]

My issue is the latter you mentioned. Too short and hard to maintain. Very sad when this happens. The conquests I received in the mail yesterday are really causing this issue.

 

[ArchStanton]

I prefer the view of 8x42 binoculars

My issue is the latter you mentioned. Too short and hard to maintain. Very sad when this happens. The conquests I received in the mail yesterday are really causing this issue.

Zeiss will send you extended eye cups at no charge. Maybe that might be worth trying.

 

[Swedpat]

A question: I have read it before but have forgot to ask: what does "eye box" mean?

 

[dorubird]

"Eye box" -how deep the eye is in the arch and what shape it has... its depends on the physiognomic architecture of each person. Some people have eyes deeper in the skull, others less so! Some have this larger cavity with prominent arches, others less so

 

[Ignatius]

"Eye box" -how deep the eye is in the arch and what shape it has... its depends on the physiognomic architecture of each person. Some people have eyes deeper in the skull, others less so! Some have this larger cavity with prominent arches, others less so

So eye box is more of a people quality than a binocular one? If so, why do the cognoscenti here talk about eye boxes of particular binoculars?

 

[dorubird]

Yes, because some binoculars have eyepieces that behave better with certain physiognomy than others. "Eye box" it is actually more a kind of combination between the eyepieces of the binoculars and the human physiognomy. That's why a pair of binoculars must be tried and tested by each individual, just like a pair of shoes.

 

[Bentley03]

I understand and accept 'the science' behind the so-called 'eyebox', it makes perfect sense. However, I have never really fathomed out why some binoculars have a reputation for being particularly finicky or unfriendly, and others of the same objective/magnification formula (8x42, for example), or even an entire model line at the various magnifications in the range, do not. The knowledgeable ones will usually maintain that it is the operator of the binocular which is the problem, not the binocular itself, insisting that it is simply a matter of setting up the binocular correctly. However, those same people also maintain that it is important to try before you buy, to make sure the binocular fits (or works for) you, eye relief and IPD allowing.

I get the theory, I don't really understand why the reality appears to be somewhat different.

I have experience of a pretty broad range of binoculars, and some I'm able to just pick up and use without thinking about them, others (despite adequate eye relief and IPD range) I simply can't, no matter how hard I try (including ages spent fiddling around with o-rings). This really doesn't bother me, apart from the fact that it goes against 'the science'.

 

[Mono]

I have only heard the term eye-box before in reference to rifle scopes. It being the point in space behind the scope you have to place your eye in order to use the scope. It is very much a function of the scope design rather than of the human face. Binoculars will have an eye-box but it is incredibly close, basically at the end of the eyecups. In contrast a rifle scope will have an eye-box many centimetres back from the occular and pistol scopes must have the eye-box an arms length away to be used properly.

 

[Swedpat]

"Eye box" -how deep the eye is in the arch and what shape it has... its depends on the physiognomic architecture of each person. Some people have eyes deeper in the skull, others less so! Some have this larger cavity with prominent arches, others less so

Thanks. That is actually what I have thought about bit did not know a word for it.

 

[Swedpat]

I have only heard the term eye-box before in reference to rifle scopes. It being the point in space behind the scope you have to place your eye in order to use the scope. It is very much a function of the scope design rather than of the human face. Binoculars will have an eye-box but it is incredibly close, basically at the end of the eyecups. In contrast a rifle scope will have an eye-box many centimetres back from the occular and pistol scopes must have the eye-box an arms length away to be used properly.

As I understand it that definition of eye box actually is the description of eye relief.

 

[Mono]

Link to Zeiss discussion on eyebox.

The optimized ZEISS eyebox - ZEISS Hunting

The eyebox is the usable area behind the rifle scope. Especially for driven hunts, a large eyebox offers a decisive advantage.

blogs.zeiss.com

 

[dorubird]

Link to Zeiss discussion on eyebox.

The optimized ZEISS eyebox - ZEISS Hunting

The eyebox is the usable area behind the rifle scope. Especially for driven hunts, a large eyebox offers a decisive advantage.

blogs.zeiss.com

now I understand better. It seems that I had a much too relative perception regarding the eyebox meaning. So a larger eye box means a greater degree of freedom of placement in relation to the optical axis. Therefore more permissive not only in relation to the distance from the eyepiece (eyerelief) but also in relation to lateral position from optical axis. But this is only possible with very large exit pupils of rifle scope. With binoculars, eyebox it is much smaler because bino it is in contact with the human face, so physiognomy becomes very important in this equation