Joachim
Sleeving bicycle rubber inner tube over binocular eyecups
Yesterday my cycle group rode out locally to Stanborough Lakes. I piloted them successfully through the back doubles of Welwyn Garden City. I had coffee and apple pie at the café by the lakes out in the sun. A happy day!
I return to my desk today, and find your posts on our other common activity, besides riding bicycles: customising binoculars to fit.
I focus my mind, and write:
1. I have gathered on the Forum that posters who intend to sleeve bicycle inner tube over binocular eyecups sometimes don't know what size of bicycle inner tube to look for.
The sizing of bicycle inner tubes is also a confusing area for cyclists themselves.
I would therefore add to the advice that you give in your post from my own personal experience: Look in the discard bin of the bicycle shop (or wherever you start your search) for starters for an inner tube marked to fit a mountain bike tyre of 2.3 inch or more maximum section.
Tubes to fit a tyre of lower maximum section will usually be too tight a fit on average diameter (say 30-40mm) binocular eyecups.
2. I have unfortunately not yet found a tube in my local bicycle shop to fit a tyre in the useful range of 2.3 - 2.4 inch of more than 2.35 inch maximum section.
There are tubes to fit fat tyres of 3 inch or so maximum section, but below the figure of 3 inch until one reaches the figure of 2.35 inch, certainly in my neck of the woods, there is a gap.
Some inner tubes are thinner than others. I am not sure that they necessarily stretch more (and so are more easy to work with) than a normal thickness tube made out of higher than average hysteresis rubber.
At this point though I am getting out of the limited sphere of both my personal experience, and my technical knowledge.
3. Eitanaltman, as I recall, found the rubber of the inner tube that he used to extend eyecups to be unpleasant to the touch.
In Britain I have never in my circle encountered tubes made out of anything else besides artificial, namely 'Butyl' rubber.
I have only ever used inner tubes made out of Butyl rubber for sleeving over binocular eyecups, and have always found them satisfactory.
But I should say that tubes can be made out of natural, namely 'Latex' rubber. It may perform differently.
Or Butyl rubber may not be as satisfactory a material to use in other climates as it is in the British climate.
4. I mention that Wllmspd got round the bicycle inner tube size problem as follows (Post #15);
Has anyone found a way to widen rubber eye-cups. I have seen lots of information on eye-relief but little on actually widening the eye cup itself. Given that everyone has different sizes of eye-sockets, it would stand to reason that binocular companies would recognize that and provide some...
www.birdforum.net
'Tyre labelling is a load of hurt, I bought what I thiugh I would fit but failed. So I bought one super ultra huge fat-bike tube and slice bits off as I need. You can then cut it so you have a long strip, then you can use contact adhesive to tune the exact diameter you want. I tried stretching, but the unstretched bit tends to construct the eye lens width. I prefer a light friction fit as sometimes I need to adjust the inter-eye correction or I am using individual focus binoculars and So I want to be able to rotate the cup about. I played about with wing design and some scissors... once I had one I like I just trace round it for other eyepieces. I have custom ones for a range of binoculars and other eyepieces... all for the cost of one fat bike tyre and a tube of glue. The roll down design is helpful if you want to use glasses and get closer.'
Regards
Stephen
PS I've started experimenting with extending the objective barrels of my Opticron 8x32 SR.GA using your method, except that I cut the stiffener from a 'hard' plastic milk bottle.
[The idea was to add a bit of light shielding, but I found out unexpectedly that the shields also, by way of improving the ergonomics, sorted out the balance problem of the Opticron in my hands]
I just managed to do the job with inner tube to fit 2.35 inch maximum section tyres, but it was ultra difficult, and I could easily have damaged the binocular.
I shall probably therefore try Wllmspd's method for the job next time.
Or perhaps duct tape if I can find some that has a matt finish!
