How Much Eye Relief Do I really Need?

[HoosierGuy]

Since I got my first pair of really good binocs - Nikon Monarchs 8x42, I'm becoming more aware of the important things like eye relief, field of view, and such.

As I try to find a good pair of higher power binos in the 9x to 10x range, at a low price, I'm always looking at eye relief. Since my Monarchs have 19.6 (I think) eye relief and I always wear glasses, I always look for binos with at least 19 eye relief.

But, do I really need 19mm eye relief? I wear glasses. The glasses sit on my nose normally, not close to my eyes and not on the tip of my nose, but normally. I'm happy with my Monarchs.

So, would I get good eye relief with 18mm or 17mm or even 16mm? I've read if you wear glasses don’t' go below 16mm. But I've also read from bino users not to drop below 19mm and maybe go for 20+mm.

So, how low can I go with eye relief?

I'm talking about binos for birding. 9x to 10x.

Much Thanks!

[Kevin Purcell]

What you want is the "correct" ER for you: the one that puts the exit pupil coincident with the entrance pupil of the eye (the iris).

It depends on your prescription (myope/near or hyperope/far? how strong?). Myope glasses with a negative prescriptions lengthen the effective ER. Positive prescriptions shorten it.

It depends up how closely your glasses fit i.e. how far the eyeglasses are from your eyeball. This isusually taken as 12mm but it varies by plus or minus 5mm depending on your glasses.

It depends on what the maker means by his ER number? The technically correct: ER from the backside of the last ocular lens? That gives the biggest numbers. Or perhaps more useful: the usable ER. From the closest point you can place your eye (well eyeglasses) which depends upon how the ocular lens mount and eyecup are designed.

Throw in a couple of mm for lens thickness to (that goes up with your prescription) depending on the thickness of your eyeglass lens. Again hyperopes get screwed with their lens being thickest in the center.

Answer: Only you can know by checking out the bins.

For me I tend to have more problems with modern bins with blackouts and too much ER rather than too little!

If you have more than one pair of glasses you can "tune" them to the ER.

Search for "eye relief" amongst my posts ... I've talked about this quite a few times. In great detail.

[Swedpat]

Hi HoosierGuy!

I think I am in the same occasion as you are. I need long eye relief and mostly close to 20mm. I think Monarch 8x42 is quite comparable to Swarovski SLC 7x42 in this case. I have the Swarovski SLC7x42 and have also tried Monarch 8x42. Maybe you will make it with 2-3mm less eye relief than these have. But remember that the stated numbers of eye relief isn't always comparable. You have to try before yoy by. Nikon SE porro glasses are stated to 16mm eye relief and works well for me.

Regards, Patric

[spyglass2]

15mm seems to be about the minimum if you need to wear specs....and then only if they sit as close to yr eyeballs as possible. 16 is good, 17 is probably ideal and really all ya need. My 7x42Discoverer has 20, and I've put a 2mm thick neoprene grommet (actually faucet seal rings from Ace Hdwe) under the eyepiece flange to decrease the relief a little. In a perfect world, I'd be able to transfer about 3mm of the excess on the Discoverer to my Swift 820, which, although has stated 17mm, actually has only about 12. That would nearly make my optics life complete, altho even with that, I suspect perfection in that realm is a pipe dream.....sigh

[J. Moore]

As others have stated, you cannot trust the numbers since different companies measure differently. Take them only as a rough indication of the amount of eye relief, and using 19 as an absolute cutoff probably means you are eliminating many binos that have adequate ER for you. Trying is the only way to know for sure.

Best,
Jim

[Kevin Purcell]

As others have stated, you cannot trust the numbers since different companies measure differently. Take them only as a rough indication of the amount of eye relief, and using 19 as an absolute cutoff probably means you are eliminating many binos that have adequate ER for you. Trying is the only way to know for sure.

For example with my fairly close fitting glasses I find I get the whole field of the Yosemite 8x30 with a speced 14mm ER.

I find too much ER to be a much bigger pain than too little. Blackout suck more that loosing the edge of field.

But as both J. Moore and I say you need to try. The only time I feel confident in extrapolating is between same or very closely related designs from the same company when I've tried one of them. But in general even that doesn't work too well: different eyecups design with different offsets make the predictions less reliable.

[HoosierGuy]

So when I'm in a sporting goods store with binos I need to try a lot of them out, not only focus on image but eye relief, and field of view, and etc...

My brother has so many cheap binoculars that my Nikon Monarchs almost made me cry - I could use both eyes! I could keep my glasses on!

[statestat]

I also suffered from choosing between wearing my eye glasses and seeing the full field through the binos or leaving the glasses on, and have tunnel vison, until I found the Steiner Peregrine XP, in 8x44. Eye relief published at 20mm. You have recived good advice, try as many pair as possible. I purchased some binos on the net based on the published eye relief and was usually disapointed. Once I picked up the Peregrines and tried them with glasses I could not put them down. Now I can spot the birds with my eye glasses on, and then just put the Peregrines up to my eyes and what a view. It is almost magical on how I can see everything without worring about eye placement. I only hope you can find a pair that works so well for you. I even took my Lecia 10x42 to my eye doctor to get eye glasses fitted to the binos and he thought I was nuts and was not too helpfull, so really trying a lot of binos is the best bet.

[Kevin Purcell]

I also suffered from choosing between wearing my eye glasses and seeing the full field through the binos or leaving the glasses on, and have tunnel vison, until I found the Steiner Peregrine XP, in 8x44. Eye relief published at 20mm. You have recived good advice, try as many pair as possible. I purchased some binos on the net based on the published eye relief and was usually disapointed. Once I picked up the Peregrines and tried them with glasses I could not put them down. Now I can spot the birds with my eye glasses on, and then just put the Peregrines up to my eyes and what a view. It is almost magical on how I can see everything without worring about eye placement.

I've tried the Peregrine XP (and still have to write up the review) but I found that the ER was WAY TOO LONG for me! I had to use them with about 5mm or so of eyecup which mostly worked except the eyecups aren't stopped and they would drift a little. So given other ER numbers I can well believe that with the eyecups fully down the exit pupil is 20mm behind the lens.

But I would guess statestat has any of: thick glasses; glasses that aren't close fitting; deepset eyes and is maybe a hyperope (has a positive prescription). These all add up to place the eye's entrance pupil further back from the front surface of the bins ocular.