What does it mean that binoculars with larger lens diameter are more comfortable? (1 Viewer)

F

Fjodor

Member

• Jul 1, 2014

• #1

Hi,

I've often heard that larger binoculars with larger lens diameter are more comfortable to use. E.g. it is more comfortable to use 8x42 vs 8x25 binoculars.

But what exactly does that mean? In what way are larger binoculars more comfortable? Can someone please try to explain that.

Thanks!

 

Hermann

Well-known member

• Jul 1, 2014

• #2

Fjodor said:

Hi,

I've often heard that larger binoculars with larger lens diameter are more comfortable to use. E.g. it is more comfortable to use 8x42 vs 8x25 binoculars.

But what exactly does that mean? In what way are larger binoculars more comfortable? Can someone please try to explain that.

Click to expand...

Larger objective lenses mean that the binocular's exit pupils are also larger. It thus becomes easier to keep the eye's entrance pupil aligned with the binocular's exit pupil. Given that on a "normal", overcast day your exit pupils are likely to be about 2.5mm, binoculars with exit pupils >2.5mm are likely to be far easier to use. This becomes most obvious in prolonged use or on windy days, or when're you're tired.

I personally don't use any binoculars with exit pupils <4.0mm for everyday birding. Compacts with their small exit pupils are OK to have a quick look - but I don't really like using them for "real" birding.

Hermann

 

F

Fjodor

Member

• Jul 1, 2014

• #3

Ok, I see. And what problems does it cause if the exit pupil is too small? What happens if the eye's entrance pupil is not aligned with the binocular's exit pupil?

 

perterra

Well-known member

• Jul 1, 2014

• #4

Fjodor said:

Ok, I see. And what problems does it cause if the exit pupil is too small? What happens if the eye's entrance pupil is not aligned with the binocular's exit pupil?

Click to expand...

Depending on how far out of alignment, all you may see is black.

 

C

ceasar

Well-known member

• Jul 2, 2014

• #5

Large binoculars with large objectives and large eyepieces usually have large eye cups with wide rims and these are more comfortable to use. It is easier to brace them up against your eyebrows which is a good way to keep the binocular steady.

Bob

 

WJC

Well-known member

• Jul 2, 2014

• #6

Hermann wrote: "Larger objective lenses mean that the binocular's exit pupils are also larger."

What if the magnification is inordinately large? The exit pupil is not the size of the rear eyelens. Case in point: the Fujinon FMT-SX and FMTR-SX have rear eyelenses just over an inch wide. However, the optical exit pupil is just over 7mm. To determine the size of the exit pupil, divide the clear aperture of the objective lens (in millimeters) by the magnification. That said, the larger mechanical exit pupil does make it more comfortable to use, and it allow one to wear classes and still be able to see the whole field. Some people, new to binos with good eye relief, complain of having too much. That, however, if much like riding a bike. When you get the hang of it, it becomes second nature.

Bill

 

Last edited: Jul 2, 2014

F

Fjodor

Member

• Jul 2, 2014

• #7

WJC said:

Some people, new to binos with good eye relief, complain of having too much.

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Hmm... how can it ever be bad to have good eye relief in binoculars? What drawbacks are there?

 

WJC

Well-known member

• Jul 2, 2014

• #8

Fjodor said:

Hmm... how can it ever be bad to have good eye relief in binoculars? What drawbacks are there?

Click to expand...

Not knowing, intuitively, exactly where to place your eyes relative to the eyepiece. It has never been a problem for me, and probably won't be for you. I guess for some it can be a problem, but I've never seen a need to make it an issue.

Enjoy, and don't go looking for issues; enough will find you on their own! :t:

Cheers,

Bill

 

Last edited: Jul 2, 2014