Eitan
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.
Stephen
* 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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