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widening eye-cups (1 Viewer)


Out Birding....
United States
I'm glad I helped.

WJC reminds us that the importers etc are in the business of sourcing binoculars, not dispensing worldly love.

I would suppose one can expand that to: 'The business of sourcing high value items like binoculars', the problem of small value items like accessories being that they take just as much trouble to source and import, for much smaller reward.

The small man does not fill the gap because he/she cannot discount the cost of getting his product to market against a sufficiently high price that is also acceptable to the consumer.

Or some such!

I encountered the problem in the field of cameras.

The Chinese manufacturers churn out cheap red dot sights in thousands for hunters, paint-ballers, etc, but when I bought mine there was just one small man right round the world, and one factory making the mounts to fit them to a camera hot shoe.

Later the small man circulated that he had had to lower the specification of the mount because rising costs meant that he could no longer make a profit on sales of the present model.


I find that interesting..... I know when I worked in 'retail' ...(30 years ago), the value of add-on accessories was where much of the profit was. Sell a product for X $'s and sell that add-on accessories to increase the profit.

But I also realize that optics (cameras and bin, and lens etc) have fairly low profit margins and but sell for quite a bit of $. So tagging on a minimal dollar or euro for an accessory isn't going to really pull in profit.

Stephen Prower

Well-known member

At the height of the boom in the sale of desktop computers, a retailer told me that the box shifter's entire profit was represented by the £10 charge for post & packing.

That was a time when the salesman's job for in store purchases was essentially to to sell high-priced accessories (and also, as I read, unnecessary purchases, such as unlikely to be claimed under extended warranties*).

I don't remember if essential items of kit were sometimes deliberately not included in the in store price of a computer so that they could be sold as accessories, but wouldn't be surprised if that happened.

The Greens did a good job in past days when they concentrated more upon practical commercial issues that we could all agree on, such as the above, or--my particular bugbear--planned obsolescence*, rather than political issues.


* The rule of thumb was that, if a computer was going to go wrong, it was by far the most likely that it would go wrong in the first year after sale

** Apple is notorious for it. But on a more mundane level, I believe Robinson Willey used to stock spare parts for models of their gas fires that were up to 25 years old. So I was not pleased a couple of years ago when mine needed a vital spare part to learn from the fitter that Robinson Willey had since reduced the period to 10 years
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Well-known member
I have daytime, night time binoculars and...

Peter, a bit off topic, but I see you have a 10x50 APM ED APO. I'm seriously considering that particular binocular, given that it's half the price of quality roof binoculars which I would actually use mostly for stargazing. What do you make of it? Thanks and sorry for off-topic-ing ;)


Well-known member
More on topic that it has got. The 10x50ED are nicely wide and sharp to practically the edge, they are quite chunky and solid though you can hand hold. The eye lenses are quite big and they pinch my nose slightly. I got them purely for night time use, but they’re very nice optically in the daytime (though individual focussing is less ideal). You can buy ring cheap adapters add 2” filters to the objectives if you want. They are considered the equal of the famous fujinon 10x50fmtx but cost a fraction... a no brainier really. I don’t like narrow fields of view and I have developed a dislike of the way bright stars can change shape round the edges in less well corrected models.



Well-known member
Peter, thank you very much for the detailed explanation. It is really helpful. I couldn't agree more on your comments about useless superwide FOV for stargazing. My idea is to used them mainly for that as well. The weight remains a big concern. I've borrowed a pair of 7x50 Fujinon to see how I like the feeling/weight/bulk and will decide upon that (although probably the similar weight of the Fuji is less critical being a 7x, and the vibrations can get more worrying in a 10x). Thank you again, also for the tips on the filters. What do you use them for? Eclipses or regular stargazing, nebulae, etc.?


Well-known member
have several kg class bins like the 10x50. You can hold them fairly steady by hand if you brace your arms, but better if mounted. They come with a solid tripod adapter. I’d get a monopod and trigger ball head as shown here: http://binocularsky.com/binoc_mount.php
10x50 will show fainter stuff and have a wider apparent field of view, unless you need the large exit pupil of the 7x50 (which nearly universally have quite narrow fields of view).

Use them standing or better when reclining in a garden chair. If you slump down and jam the monopod in the ground by your feet you can even reach the zenith…. not something you can do with a tripod.
I’ve used mine in the daytime occasionally and then at night when I don’t want to drag out heavier stuff, lovely small stars. For nebulae I’d probably go larger to get image scale (not that many are visible from an urban location) and for solar stuff I have dedicated kit.



Well-known member
Peter, thanks again, this was most clarifying. Never thought of the monopod+triger ball combo, but it is seriously worth considering! I'm not a big fan of tripod for the kind of stargazing I do. I mean, I use the scope on a tripod (not an astro telescope, I know), but what I really like about binocular stargazing is especially the capacity of hovering around, star-hoping, and basically surfing freely through the stars, so the monopod+trigger ball does seem a really attractive prospect :) Thanks!


Well-known member
Here are step by step instructions for ordinary eyecups -- Constant diameter, no lumps and bumps:


Stephen - wanted to thank you for this idea. Finally had a chance to try it out; we have a friend who owns a bike shop and he gave me an old inner tube to play with.

Here are some photos of the results on my Pentax 9x32 AD WP (Sightron clone). The narrow diameter, hard edged eyecups of the Sightron and its clones was always my least favorite part of these binoculars. Not only do I dislike the feel, they are also too long for the eye relief so you I have to use them at an intermediate position, but the detents are weak and they always slip from the position I want.

Added the doubled-over sleeve with the inner tube has totally changed the ergonomics for the better! The increased diameter and softer edge are much more comfortable in my eye socket. And the extra friction from the rubber (and the o-ring I added) means the eyecups no longer slip from the mushy detents.

With a little bit of effort I managed to get it nice and even, it almost looks like it was not an add on! The inner tube was a bit smaller diameter than I anticipated though, so it was tight to stretch it and slip it on, but the side benefit is I cut a little extra length so it “wraps” around the ends of the stock eyecup and the doubled over edge contracts in a bit, adding a little taper at the point of contact. I will grab a larger diameter tube next time I see him and play some more. (I wasn’t too concerned about damage since these are cheap binoculars and this was really proof of concept).

I really don’t understand why some binoculars have needlessly narrow diameter eyecups. It’s one thing if it’s a 20-25mm objective where the tubes are super narrow, but the modified Pentax/Sightron eyecups are now a similar diameter to the optical tubes. The Swaro CL 30 and Meostar 32 are two others that for some reason have eyecups much narrower in diameter than the optical tubes; I’m excited to try this on the Meostars when they return from their transatlantic voyage to the Czech Republic.

My one quibble is the texture of the inner tubes. It’s kind of tacky / sticky and not nearly as pleasant to the touch as nicer eyecups (like those on the Leica UV or Nikon EDG). Does anyone know of a way to soften the texture? Or is there an alternative material that is more pleasant to the touch?


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Stephen Prower

Well-known member

That's a very happy post to receive!

I shall quickly give you a part answer your last question:

My one quibble is the texture of the inner tubes. It’s kind of tacky / sticky and not nearly as pleasant to the touch as nicer eyecups (like those on the Leica UV or Nikon EDG). Does anyone know of a way to soften the texture? Or is there an alternative material that is more pleasant to the touch?

And I shall hurry to answer the rest of the post as soon as I can.

I started using bicycle inner tube to customise binoculars four, or maybe five, years ago. I have never had any problem of the tube going sticky.

I should say though, specifically, 'butyl rubber' bicycle inner tube, because I have checked my memory from the web, and there are two sorts of rubber currently used in making bicycle inner tubes, butyl rubber and latex rubber.

I have never heard any fellow rider in conversation say that they use latex rubber tubes. I have never seen, let alone used, a latex inner tube. Perhaps it's the circles that I mix in!

But on the web I found an advert by Chain Reaction Cycles for a 'Michelin C4 AirComp Latex MTB Bike Tube' at the seeming very reasonable street price of £7.99 (Manufacturer's recommended retail price £13.49), and the spiel:

'The natural elasticity of Aircomp Latex tubes can actually improve efficiency by reducing rolling resistance. Latex has a remarkably high modulus of elongation (700%!), giving it outstanding resistance to punctures and pinch flats.

It's the perfect complement to today's high-performance wheels and tyres. The Aircomp Latex weighs just 130 grams (C4 MTB version), making it one of the lightest tubes available. ...'

That's a big clue.

It's the inner tubes for the large section tyres now used by many mountain bike riders (if they haven't gone tubeless) that are most useful for customising binocular eyecups.

So all I can suggest is that your friend who owns a bike shop may have thought to have been ultra helpful by giving you a discarded inner tube from a fat-tyred modern mountain bike.

In support, I wouldn't be surprised if butyl rubber inner tubes only had historically a small sale on the market, certainly for fat-tyred mountain bikes, and have now been largely supplanted by latex inner tubes, or tubeless tyres.

If so your friend would perhaps have been more likely to have a latex tube to hand to give you than a butyl rubber tube.


Stephen Prower

Well-known member


Further to the last post, I am too late to correct an error 'invisably'.

'I wouldn't be surprised if butyl rubber inner tubes only had historically a small sale on the market, certainly for fat-tyred mountain bikes'

should read:

'I wouldn't be surprised if butyl rubber inner tubes only had historically a small sale on the market for fat-tyred mountain bikes'


Stephen Prower

Well-known member

Here's the rest of the answer to your post dated 13 September (#29).

It's a long one!

1. Potential use of O-rings

I see you have access to a sufficient variety of O-rings to have found ones of the right size for the job on the Pentax 9x32.

I have not yet done a search of local shops for a source.

O-rings may supply a mechanically 'friendly' means of freezing the diopter adjuster of my Opticron 8x32 SR.GA.

2. 'Changed the ergonomics for the better'

I'm most happy, as I said, that you're pleased with the way that the job has turned out. I admire the tidy cosmetic result. You don't exaggerate. The 'new' eyecup does look to my eye too like a regular manufactured eyecup.

If you've now got the customising bit between your teeth, I attach photos of my fully customised, right down to wings and rainguard, Bushnell 7x26 Custom Elite.

I achieve an eyecup width of 40mm (compared with an original width of 30mm) by adding one section of inner tube freezing the eyecups in the up position; one doubled over section of thickish gauge tubing effecting the main bulking out; and one section carrying the wings.

The Bushnell is now, as customised, a good fit to my face. My eyes are located immediately at the point of eye relief.

3. 'I really don’t understand why some binoculars have needlessly narrow diameter eyecups'

I pass on possible optical or mechanical explanations, except for the obvious explanation that constraints may be imposed upon the designer by the stipulated small size of the binocular in question.

(In passing though I note that Nikon managed to distinguish its Sprint series of reverse Porros from the general run of reverse Porros with 30mm diameter eyecups by giving them, if my 7x21 Nikon Sprint is typical, 35mm diameter eyecups.)

Dispassionately, one has to accept that it could be an ergonomic issue*. Marketers simply get the physical facial profile of the target market wrong.

But I don't pass on the possibility that designers of some binoculars may have been influenced in the choice of the diameter of eyecups by the marketing side of their company to prefer appearance to function.

The marketing side fear, and I am afraid may fear rightly, that potential customers will be put off by chunky eyecups.


* The ergonomic context of customising the width of eyecups is that the location of the eyes at the point of eye relief of a binocular is theoretically assured by three dimensions of binocular and subject:
- The height of the point of eye relief of the binocular
- The height of the rim of the eyecup of the binocular
- The inter-pupillary distance of the subject.
The height of the point of eye relief of the binocular, and the IPD, are fixed dimensions, and the height of the rim of the eyecup of the binocular is usually now an adjustable dimension.

However when the eyes are presented to the binocular, unless the eyes hover over the rim of the eyecups, the location of the eyes over and at the point of eye relief will be determined by the location of the points of contact of the face of the subject with the binocular.

The location of the points of contact of the face of the subject with the binocular:
- As to the binocular, are determined by a fixed dimension, the width, ie radius, of the eyecups, and an adjustable dimension, the distance separating the points of eye relief, as determined by the setting of hinge of the binocular
- As to the subject, are determined by the facial dimensions of the subject. The fact that people's facial dimensions vary considerably is well known.

The potential usefulness of transforming the width of the eyecups from a fixed dimension into an adjustable dimension too like the separation of the eyecups is that, by adding points of contact at the sides of the nose and the browridge, it may assist the subject in the task of correctly locating his or her eyes at the point of eye relief.

In particular it may assist subjects who are missed by the 'One size shall fit all' target of the designers of binocular eyecups



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