Eye relief - rule of thumb method? (1 Viewer)

[Themoog]

Wondering if someone could clear this up for me.


Picture if you will a pair of binoculars placed flat and at maximum ipd (just for steadyness) By flat I mean horizonal, mimicking the position they might be held in during use.

I place a steel ruler against the edges of the eye pieces where they touch the paper whilst they are in a retracted position i.e. For use with glasses.

I make a fine pencil mark along part of the ruler edge that is in contact with the outer rims of the eye pieces. Mark A.

I carefully extend the eye pieces to their full extent, re-lay the ruler in position again and make a second pencil mark. Mark B

Is the gap between mark A and B reflective of the eye relief?

I'm working on the principle that whilst some will hold an eyepiece slightly closer or further away depending on comfort, bone structure, glasses use and blackout relief there must nevertheless be a fixed plane at which the light being transmitted comes together most expediently otherwise there cannot be an agreed protocol for establishing relative and absolute ER. Also, rarely are the objective face of a pair of glasses entirely flat but largely convex and of course, the eye lense/contact lense is convex.

Setting that aside and not looking to be more that 1mm in error, have I understood this correctly and would this method be a reasonable way of establishing ER, rule of thumb?

I understand manufacturers vary in their methods in measuring ER but I suspect it would be;

a) from the surface of the occular to the front edge of the eye piece surround at it greatest extent
b) as described above
c) half way between the surface of the occular and the back edge of the eye piece in its fullest deployment i.e. A mean average between a) and b).

Could I also ask which manufacturers use which method? (and or something completley different if I'm having a senior moment- for which I apologise in advance for wasting your time with)

Many thanks

Tm

 

[pete_gamby]

We measure from the outmost/top edge of the eyepiece in its lowest position (twisted down or folded down) to the point at which the exit pupil diameter is measured to be at it's maximum/optimum e.g. 5.25mm for an 8x42 binocular. This is done using a device with an extendable tube which projects the exit pupil onto a semi-translucent sheet with a scale.

HTH

Cheers, Pete

 

[jring]

We measure from the outmost/top edge of the eyepiece in its lowest position (twisted down or folded down) to the point at which the exit pupil diameter is measured to be at it's maximum/optimum e.g. 5.25mm for an 8x42 binocular.

Which is the honest way of doing this - quite often the numbers are given measured from the eyelens which might be deeply recessed thus limiting usable ER.

Thank you Pete for the explanation!

Joachim

 

[Troubador]

We measure from the outmost/top edge of the eyepiece in its lowest position (twisted down or folded down) to the point at which the exit pupil diameter is measured to be at it's maximum/optimum e.g. 5.25mm for an 8x42 binocular. This is done using a device with an extendable tube which projects the exit pupil onto a semi-translucent sheet with a scale.

HTH

Cheers, Pete

Pete

Thanks for this explanation of how you do it. Am I right though in thinking that actually this dimension will change from unit to unit due to (among other things) variation in the precise positioning of the threads that locate the eyecups in the optical tubes as well as variations in the dimensions of the cavities that mould the components that make up the eyecups as well as differing shrinkages of the plastic from mix to mix? I guess these variations are individually very small and that some times they cancel out but perhaps they sometimes add up to a measurable difference. I can imagine it would be impossible to come up with a publishable dimension for this due to the possible variations. Or am I exaggerating or just plain wrong??

Lee

 

[Themoog]

Think I get it...ish

We measure from the outmost/top edge of the eyepiece in its lowest position (twisted down or folded down) to the point at which the exit pupil diameter is measured to be at it's maximum/optimum e.g. 5.25mm for an 8x42 binocular. This is done using a device with an extendable tube which projects the exit pupil onto a semi-translucent sheet with a scale.

HTH

Cheers, Pete

Thanks very Pete.

Would that be the same as saying you protect the the occular end with tubes to prevent incidental light from interfereing with the measurement and then allow light in through the object end, then use this sheet as a form of (for want of a better term) 'focal plane' pressed flat on the end of the tubes.

You they extend/retract the tubes until the circle of light falling onto the sheet is precisecly equal to the effective apeture for the given configuration e.g. 5.25/f5.25 and then read off the pre-calibrated markings on the sheet when the diameter of the beam is 5.25mm?

Sorry for my round-the-houses, discombobulated explanation. Bit of a luddite but get there in the end....or perhaps on this occasion - not

Tm

 

[pete_gamby]

Lee - no, we don't take a multi-unit sample to account for any extremely small variations in the precise placement of the eyecup ridge. The fact that we publish to the millimetre and not to fractions should be enough to indicate the tolerance.

Tm - the exit pupil is always well-defined and the instrument design is such that stray light is not an issue. Yes, your description of the process is correct.

HTH

Pete

 

[Themoog]

Lee - no, we don't take a multi-unit sample to account for any extremely small variations in the precise placement of the eyecup ridge. The fact that we publish to the millimetre and not to fractions should be enough to indicate the tolerance.

Tm - the exit pupil is always well-defined and the instrument design is such that stray light is not an issue. Yes, your description of the process is correct.

HTH

Pete

Thanks for clarifying that Pete.

I would be curious to know if this is an industry standard, who else adheres to it and if not, what alternative methods do they use.

My method in the OP yields about a 7mm change from retracted to fully deployed. Useful as a relative figure- useless as an absolute one. There must be a better way of establishing a closer rule of thumb absolute value without needing exacting professional equipment.

It only matters to me whilst I'm unable to get out and test other gear because an ER is either going to be sufficient for an individual or it isn't. Proof of the pudding etc.
With so many choices it would be useful to have an agreed and trusted method of calibration so that the catalogues and brochures have transferrable metrics as they do with say, FOV or weight, size, etc.

(I understand that such things can occasionally get misprinted of course)

All the best

Tm

 

[Alexis Powell]

...it would be useful to have an agreed and trusted method of calibration so that the catalogues and brochures have transferrable metrics as they do with say, FOV or weight, size, etc.

A standardized method for measuring usable eye relief will never be as useful as those other metrics because the amount needed varies according to how the eyecup meets the user's face or glasses, and that varies according to the eyecup diameter.

--AP

 

[typo]

It seems different companies tend to either use the true eye relief, the distance fron the lens to the exit pupil, and others the available eye relief, the distance from the rim of the eyecup to the exit pupil, as Pete describes. A minority seem to just make it up. Available eye relief, is obviously more useful for spectacle wearers and I wish more would adopt it. I suspect the reason some don't is that the true eye relief is part of the product's optical spectification and is covered by the relevant ISO standard. Interestingly it currently allows a 5.5mm tolerance around the specified value. I think that might drive all of us to dispair.

The Nikon Monarch 7 8x30 and the Kite Lynx 8x30 are the same design, made by the same company in different countries. The Nikon lists 15.1mm ER and is just right with my close fitting glasses and the Kite with 15mm is not even close to usable. I've tried expensive models that claim 19mm, but in reality have less than 16mm available. It's a bit of a minefield.

An eyecup serves two perposes. Firstly it's a light shield and secondly it's potentially a platform to rest against your face or glasses. Often the eyecups on compacts are too small to fit round your eyeball anyway, and rarely extend enough to reach your face. At the other extreme, some get to almost 50mm across and leave no room for a nose at narrow IPDs. As Alexis says, there is almost no way to devise a fitting formula that would work for all. Hence we end up with variations of the MOLCET technique as a compromise.

Life is often a little easier if you use glasses, but still often necessary to fiddle around with O-rings and the like to get the eyecup hight just right.

With glasses you quickly get to know your minimum requirement. If it's 20mm, there is probably no point in trying those that list 16mm. Beyond that it's a bit of a lottery.

David

 

[Troubador]

It seems different companies tend to either use the true eye relief, the distance fron the lens to the exit pupil, and others the available eye relief, the distance from the rim of the eyecup to the exit pupil, as Pete describes. A minority seem to just make it up. Available eye relief, is obviously more useful for spectacle wearers and I wish more would adopt it. I suspect the reason some don't is that the true eye relief is part of the product's optical spectification and is covered by the relevant ISO standard. Interestingly it currently allows a 5.5mm tolerance around the specified value. I think that might drive all of us to dispair.

The Nikon Monarch 7 8x30 and the Kite Lynx 8x30 are the same design, made by the same company in different countries. The Nikon lists 15.1mm ER and is just right with my close fitting glasses and the Kite with 15mm is not even close to usable. I've tried expensive models that claim 19mm, but in reality have less than 16mm available. It's a bit of a minefield.

An eyecup serves two perposes. Firstly it's a light shield and secondly it's potentially a platform to rest against your face or glasses. Often the eyecups on compacts are too small to fit round your eyeball anyway, and rarely extend enough to reach your face. At the other extreme, some get to almost 50mm across and leave no room for a nose at narrow IPDs. As Alexis says, there is almost no way to devise a fitting formula that would work for all. Hence we end up with variations of the MOLCET technique as a compromise.

Life is often a little easier if you use glasses, but still often necessary to fiddle around with O-rings and the like to get the eyecup hight just right.

With glasses you quickly get to know your minimum requirement. If it's 20mm, there is probably no point in trying those that list 16mm. Beyond that it's a bit of a lottery.

David

Moving one's glasses up or down one's nose by even a tiny amount can often help a great deal.

Lee

 

[typo]

Moving one's glasses up or down one's nose by even a tiny amount can often help a great deal.

Lee

Or hinder. :-O

David

 

[Troubador]

Or hinder. :-O

David

Indeed. :-O

You could try keeping your glasses stationary and moving your nose forwards or backwards the required amount, but this is not recommended for beginners.

Lee

 

[typo]

That just makes my eyes water:-O

A frown is sufficient to extend my ER requirement by a couple of millimetres, but it has been interpreted as a look of disapproval on occasions.... sometime justifiably.

David

 

[Alexis Powell]

With glasses, tilting the head backwards a bit can help as it brings the binocular eyecup flatter against the eyeglasses rather than angling out (with a gap at the bottom). This is especially helpful when the glasses lenses and the binocular oculars are large.

--AP

 

[Troubador]

That just makes my eyes water:-O

A frown is sufficient to extend my ER requirement by a couple of millimetres, but it has been interpreted as a look of disapproval on occasions.... sometime justifiably.

David

:-O:-O

 

[Troubador]

With glasses, tilting the head backwards a bit can help as it brings the binocular eyecup flatter against the eyeglasses rather than angling out (with a gap at the bottom). This is especially helpful when the glasses lenses and the binocular oculars are large.

--AP

Yes Alexis, I have found this as well. Its a good tip. You need to take care you are still viewing on axis though or bins you thought were free from CA suddenly suffer from it.

Lee

 

[Themoog]

A standardized method for measuring usable eye relief will never be as useful as those other metrics because the amount needed varies according to how the eyecup meets the user's face or glasses, and that varies according to the eyecup diameter.

--AP

Never AS useful- true Alexis.

Useful though.

I can see with my current glasses that they have a slight curve to them. This is preventing the eyecups from making a connection at all points at once. The sweet spot on the glasses, which is fairly small as they are progressives, is located, as might be expected, in the middle of the verticle and horizonal axis.

This point is frustratingly not at the apex of the curvature. It's probably adding a few mm to my required ER on its own. Flat fronted glasses for me next time - ha ha.

All the best

Tm

 

[Themoog]

It seems different companies tend to either use the true eye relief, the distance fron the lens to the exit pupil, and others the available eye relief, the distance from the rim of the eyecup to the exit pupil, as Pete describes. A minority seem to just make it up. Available eye relief, is obviously more useful for spectacle wearers and I wish more would adopt it. I suspect the reason some don't is that the true eye relief is part of the product's optical spectification and is covered by the relevant ISO standard. Interestingly it currently allows a 5.5mm tolerance around the specified value. I think that might drive all of us to dispair.

The Nikon Monarch 7 8x30 and the Kite Lynx 8x30 are the same design, made by the same company in different countries. The Nikon lists 15.1mm ER and is just right with my close fitting glasses and the Kite with 15mm is not even close to usable. I've tried expensive models that claim 19mm, but in reality have less than 16mm available. It's a bit of a minefield.

An eyecup serves two perposes. Firstly it's a light shield and secondly it's potentially a platform to rest against your face or glasses. Often the eyecups on compacts are too small to fit round your eyeball anyway, and rarely extend enough to reach your face. At the other extreme, some get to almost 50mm across and leave no room for a nose at narrow IPDs. As Alexis says, there is almost no way to devise a fitting formula that would work for all. Hence we end up with variations of the MOLCET technique as a compromise.

Life is often a little easier if you use glasses, but still often necessary to fiddle around with O-rings and the like to get the eyecup hight just right.

With glasses you quickly get to know your minimum requirement. If it's 20mm, there is probably no point in trying those that list 16mm. Beyond that it's a bit of a lottery.

David

Amazing about the Nikon and Kite being so different ! Nothing is going to beat first hand experience for this parameter.

Agree also that part of the reason that a view without glasses is so much more immersive is that it's like sitting in a good seat in a darkened cinema.

With glasses it's always going to be a little like standing in the foyer by the swing doors looking into the darkened auditorium- if you stand in the right place you'll see the full screen but your also can't avoid seeing people queuing for popcorn out out of the corner of your eye.

Better that than no film though right?

Tm

 

[Themoog]

Yes Alexis, I have found this as well. Its a good tip. You need to take care you are still viewing on axis though or bins you thought were free from CA suddenly suffer from it.

Lee

Good points - not sure about facial reconstruction surgery as an option - at least not yet.

My glasses have little latitude off axis horizontally but becaue they are multifocus they naturall have plenty on the vertical axis.

Tilting back works well for me as my frames taper back from top edge to bottom edge. I get a much better overall rendering of solid field stop too.

Tm

 

[The-Wanderer]

Tm

Re: "This point is frustratingly not at the apex of the curvature. It's probably adding a few mm to my required ER on its own. Flat fronted glasses for me next time - ha ha."

At a well advertised high street franchise, you can buy single lens frames for £25.00. I presume that would be affordable as birding bins.

You might, depending on your age, get a free eye test too!