Eye relief? (1 Viewer)

Troubador said:

I have frameless spectacles fitted with Zeiss Drivesafe Lenses. These must be thinner than previous Zeiss lenses ......

Lee

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Lee,

We looked at the Drivesafe option when my wife was waiting for her cataract operation and was particularly having problems with glare. I didn't find much of an explaination for their claims, other than they reflect more light in the blue region of the spectrum. That would increase contrast with modern headlights. There was a slight yellow tinge to the lenses, so they might affect colour discrimination a little.

As for lens thickness, that is firstly down to your prescription and the choice of which refractive index lens. Rimless glasses need a slightly thicker lens for extra strength, so the highest index option is not usually justified. What does make a big difference is how the bridge sits on your nose, and the adjustments they make when fitting. Once you move up the Zeiss range they adjust the prescription for vertex distance. That is the gap between the eye and the lens. I discovered that two pairs of rimless frames from the same company differed in distance by 3mm and could have been adjusted even further. As it was, that made the difference between needing 14mm and 17mm ER. With a wire framed lens and higher index compound, even the 13.2mm of the Ultravid 10x32 should be achievable. At least for those with short eyelashes.

David

typo said:

Lee,

We looked at the Drivesafe option when my wife was waiting for her cataract operation and was particularly having problems with glare. I didn't find much of an explaination for their claims, other than they reflect more light in the blue region of the spectrum. That would increase contrast with modern headlights. There was a slight yellow tinge to the lenses, so they might affect colour discrimination a little.

As for lens thickness, that is firstly down to your prescription and the choice of which refractive index lens. Rimless glasses need a slightly thicker lens for extra strength, so the highest index option is not usually justified. What does make a big difference is how the bridge sits on your nose, and the adjustments they make when fitting. Once you move up the Zeiss range they adjust the prescription for vertex distance. That is the gap between the eye and the lens. I discovered that two pairs of rimless frames from the same company differed in distance by 3mm and could have been adjusted even further. As it was, that made the difference between needing 14mm and 17mm ER. With a wire framed lens and higher index compound, even the 13.2mm of the Ultravid 10x32 should be achievable. At least for those with short eyelashes.

David

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Thanks for this David and no, I don't see much to justify the 'Drivesafe' brandname either.

When I changed to frameless and the new prescription with the Drivesafe lenses my prescription had only slightly changed so I was surprised to find I suddenly needed slightly extended eyecups on binos where the screwed-down position was fine in the past. However, consulting my notes, I am reminded that my optician recommended having my glasses positioned slightly higher on the bridge of my nose so this must be the reason for the change.

This does hint at the possibility of adjustment using the position of the spectacles to help out with eye relief issues. All eyelash-length dependent of course :-O

Lee

I like to dart my eyes around, whether using bins or not, so I am partial to aviator or modified aviator type glasses. These have large lenses to provide lots of peripheral coverage, but at least for me, I find it possible to find designs that fit my face closely and that work with bins with modest amounts of eye relief (e.g. as found in many Leica models). I look for frames that (when properly adjusted) cover most of my visual field but do not contact my brow (lest I transfer a gush of sweat to the bins) or my raised cheeks when smiling (again, to avoid transfer of sweat). I wear a sweatband in summer, and I almost always wear a wide-brimmed hat to block lateral light. I don't use coated lenses because I prefer glass lenses for their scratch resistance and (unfortunately) glass are not available (at least in USA) with oleophobic coatings. Conventionally coated glass lenses seem to be especially attractive to oil, require constant cleaning, and end up being much worse (esp. after a bit of real world abuse) than uncoated glass. Incidentally, when it comes to lens thickness, I am told that in USA safety standards require lenses to be thicker than are available in the EU, so it may be more challenging to make some glasses styles work with bins here.

--AP

Kevin Conville said:

Though I don't like to wear glasses when using binoculars as I prefer contacts, I can see the full field in my Leicas with my glasses on. 8x32 and 12x50 Trinovids BTW, and we all know what miserable specs for eye relief they have!

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That's very fortunate. A lot must depend on anatomy, depth of eye socket and hence distance from eye to eyeglass lens. I couldn't use my 10x32 Leica with any glasses; I'd see maybe half the field. Fortunately I don't have to.

Alexis,
Does the U.S.A. thickness requirement for lenses apply only to glass or also to plastic lenses?

Can plastic lenses shatter and cause eye injury?

All my glasses are single vision multicoated plastic, except cheap window shopping glasses, which are uncoated glass.
But I don't use glasses with binoculars or scopes.

tenex said:

That's very fortunate. A lot must depend on anatomy, depth of eye socket and hence distance from eye to eyeglass lens. I couldn't use my 10x32 Leica with any glasses; I'd see maybe half the field. Fortunately I don't have to.

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I have wire framed glasses with relatively small eye size of 55mm wide x 29mm high, and high index glass. I have to snug them close to my face but it's doable.

I also almost never do it as I wear contacts nearly all the time. It greatly simplifies seeing generally, and binocular use is much improved. I can also use over the counter Maui Jims instead of prescription sunglasses.

Kevin Conville said:

Maui Jims

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These sound like exotic underwear............

Lee

Troubador said:

These sound like exotic underwear............

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That you wear on your face!

I don't expect you to know what these are, Lee. You see, I live in a place where people actually need sunglasses.

Kevin Conville said:

That you wear on your face!

I don't expect you to know what these are, Lee. You see, I live in a place where people actually need sunglasses.

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:-O:-O:-O
If Maui Jim also sells waterproofs and rubber boots he could do well over here.
Lee

Binastro said:

Alexis,
Does the U.S.A. thickness requirement for lenses apply only to glass or also to plastic lenses?

Can plastic lenses shatter and cause eye injury?...

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I don't know. Will ask my eye doc next time I get a chance. Maybe someone else knows.

--AP

Binastro, Alex-

I googled and found this:

"Actually, this issue is fairly complicated, and even confuses many people
in the ophthalmic industry. First of all, the only lenses which have to
meet a specified minimum thickness are lenses which are sold as "safety
glasses". These must be no less than 3.0mm at the thinnest point on the
lens.

Although regular eyeglass lenses do not have a specified minimum
thickness, they nonetheless have to meet the FDA requirements for "impact
resistance." For glass lenses, this means that the lenses must undergo
heat or chemical tempering, then subjected to a "drop-ball" test (a 5/8"
steel ball dropped from 50 inches.)

Plastic lenses do not require special treatment or testing. They do,
however, require that lens manufacturers state under what conditions their
lenses will meet the FDA impact requirements. For each specific lens
material, lens manufacturers do this by "certifying" their lenses will
meet these requirements when processed to a certain minimum thickness and
processing standard. These recommendations are based on exhaustive and
continuous "batch" testing done as part of the manufacturing process. Any
lenses ground thinner than the manufacturers' recommendation will not be
in compliance with FDA impact requirements, unless the grinding laboratory
is willng to conduct their own tests. Since the drop-ball test oftens
mars the surface of plastic lenses, this is not a practical option for
most laboratories.

The upshot of all this is that a "standard of care" has developed
concering minimum thickness for various lens materials. For CR-39 lenses
(the lens material in about 70% of all eyeglasses in the U.S.), all
manufacturers that I'm aware specifiy a minimum center thickness of 2.0mm.
Minimum edge thicknesses depend on overall lens power. Some "high index"
and polycarbonate lenses are certified to meet impact requirements at
1.5mm centers, and, in some cases (very high minus powers), even as low as
1.0mm thickness.

I hope this helps clarify rather than confuse the issue. :->

Regards,

Steve
Sola Optical, USA"

Thanks Kevin, that's interesting stuff. I can't find the equivalent info for the EU but I'm sure something similar exists.

My lenses are 1.6 index so probably Mitsui Chemicals MR-8 which is rated very good for impact resistance. That compares to polycarbonate excellent and CR-39 good. In their illustrative examples, which appear geared for the US market, the minimum edge thickness is 1.5mm and centre thickness 1.4mm. For CR-39 is is 2mm for both. In practice that's prescription and frame dependant of course.

David

@ Bill / Chuck: Thanks for your advice!

I've checked out a 8x42 Noctivid at our local Leica Store today. Eye relief / ease of view is just perfect for me and my spectacles (eye cups fully retracted). Let's see to where this positive experience will lead me...

Tom

Lightbender said:

@ Bill / Chuck: Thanks for your advice!

I've checked out a 8x42 Noctivid at our local Leica Store today. Eye relief / ease of view is just perfect for me and my spectacles (eye cups fully retracted). Let's see to where this positive experience will lead me...

Tom

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Tom, That's great news that you found a binocular that gives you the whole field.
In addition, it has excellent optics, so its a win-win, except for your pocket book...

If you want to shop for less pricey alternatives, you might check out the Zeiss Conquest 8x42 HD, and also the Vanguard Endeavor edII 8x42. Make sure your IPD works for them as well. Unless, of course, you've already tried these.

-Bill

Eye relief is a tricky thing for me. I can look through Nikon EII or Swift Audubon with short eye relief and no blackouts. I recently had to send back a pair of Leica Noctivid 8x42 because even at 18mm ER I was getting blackouts in certain portions. Yet my Leica Trinovid 8x32 BN with shorter eye relief is no problem. I use binoculars without eyeglasses.

Coolhand,

Interesting for someone to have blackouts not wearing glasses with 18mm eye relief. Is it possible that it was a flawed sample? I think you have experience with the EDG, how were they regarding eye relief.

Andy W.

dries1 said:

Coolhand,

Interesting for someone to have blackouts not wearing glasses with 18mm eye relief. Is it possible that it was a flawed sample? I think you have experience with the EDG, how were they regarding eye relief.

Andy W.

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Sounds like too much eye relief rather than not enough. Some people have similar issues with the Zeiss Conquest HD.

What is important is that the required eye relief of the individual (whether wearing glasses or not) matches the eye relief offered by the binocular (either through sufficient eye relief in the first place and/or being able to precisely adjust the eye cups to suit - this means they need sufficient range to accommodate that).



Chosun :gh:

Thanks Chosen, perhaps the same plight has happened to Kingfisher regarding the Noctivid, is that why longer/different eye-cups were provided for the Conquest.

Andy W,

dries1 said:

Thanks Chosen, perhaps the same plight has happened to Kingfisher regarding the Noctivid, is that why longer/different eye-cups were provided for the Conquest.

Andy W,

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Chosen and Andy, I think you are right. I am thankful that there are a few binoculars that actually fit me really well WITH my glasses on. But its clear that when they accommodate me, others that don't need glasses may have a problem with the same binocular. But then, maybe 95% or more of all binoculars made fit the folks that don't need glasses.

-Bill

Bill,

Lack of adequate eye relief seems to be the more common issue with not being able to see the entire FOV, but aside from facial features and getting a glass to fit the bridge with sufficient IPD (we have all had one glass that just did not fit), the subject of too much eye relief perhaps needs to be discussed more often.

Andy W.