A double image problem caused by eye problem

[richard5700]

Hi. Years ago I had an accident and damaged my eye socket. Ever since when I look at stars through binoculars I see two images of a star.  Because of the misalignment of my eyes the spacial separation is too great for my brain to combine the images from the right and left eyes.  I'd love to buy a pair of observation / angled binoculars (not cheap) , but I fear it would be a waste because of this eye problem. Is there a solution so I could use binoculars without seeing a double image?  Thanks.

[GlenM]

I'm not sure but it sounds like the binocular is not collimated to me. Perhaps it could be a prism out of collimation. Is it all binoculars?

 

Glen.

 

[Peter Drew]

It should be possible to optically decollimate a binocular to address your problem, it's just the reverse procedure to that applied to an out of collimation binocular that is giving double images to someone without an eye problem.   😀     

[richard5700]

Previously, I've never had a problem with double image with any binocular I have ever bought or used.  So, naturally, I'm wondering if my eye misalignment is too great for any pair of binoculars to provide a single image of a star.  I'm assuming that the binoculars I am using are collimated correctly  as per the factory setting.  I have no problem when using binoculars for terrestrial observation.  The binoculars I am using are "MEADE 10x50", also called "PORRO 10x50".   Has number: 4007922 144276. Bought them from LIDL some years ago for £10.  Tonight I'll try another pair of binoculars and see what gives.

EDIT: Point taken, must decollimate. 🙂

Edited August 28, 2019 by richard5700

[richard5700]

Hi. Actually, I don't think I can locate screws to adjust the prism. I've peeked under a rubber covering but nothing seen. So, I may need to use a method not involving prism adjustment.

EDIT:  Unscrewing the objective lens I see the prisms are held in my a flat spring, and the prisms are cemented into place.

I suppose with something like a pair of expensive observation binoculars, to decollimate (or whatever it would be) if really necessary, would be easy peasy. And hopefully easily reversed.

Edited August 28, 2019 by richard5700

[Peter Drew]

If you marginally unscrew the objective barrels you usually find that the stars move out of alignment. By trial and error whilst looking through them at a star you should be able to find a position to suit you. If you do, mark the positions and then fix them with adhesive.   🙂

[DaveL59]

hi Richard

Porro designs I've worked on don't all have prism tilt screws, some use small shims under one side of the prism to achieve tilt, tho these are not adjustable without dismantling. Al have a metal strap to secure the prism and some cemented also. Cemented prisms do mean you can't easily tilt them to adjust but that's not to say that the prisms weren't shimmed to the required tilt and then cemented so they can't easily move. The other method is to have the prisms set into place and correctly aligned to each other and mount the objectives in an eccentric ring, so you adjust alignment by rotating the ring which alters the image position at the eyepiece.

As Peter says, if you can unscrew one objective barrel a little you may find the image diverges/converges to suit your optical requirement. If that's the case then the objective lenses may well be eccentrically mounted and that'd be where you would adjust collimation. Only thing then is if you've had to unscrew more than a tiny amount the barrel can tilt a little in use, or work looser, neither of which would help the image stay "true" to your adjustment over time or even during use.

If the body is fully rubber coated then unscrewing the barrel would mean cutting/removing the armour and reducing any resistance to future moisture ingress. If that's the case take a close look at the objective end. Usually there's a beauty ring, or you'd peel the rubber coating away a little to reveal the lens retaining ring, below that would be the eccentric rings. Ideally you need a lens spanner to be able to slacken and remove the retainer without risking damage to the lens though, 2 small screwdrivers can work but one slip and... Adjusting eccentrics can be time consuming, working out which way to turn and the effect on the image, not losing position when tightening the retaining ring up etc, but can be done if patient.

I'd suggest only work on one side initially and see how that goes. Do you know which eye of now slightly offset, or is the condition affecting both?  Just thinking if it might be best to start with the one that you know is offset and adjust that side of the bino first. If both then adjust for your less dominant eye, perhaps? This is just a guess tho, ideally you don't want to offset the alignment on one by very much so you may end up having to make a smaller adjust on each objective to get a better balanced image for you. 

Worth noting also, these would then be specific you your needs, nobody else would be able to use them without getting the effect you currently do and eyestrain/headaches.

[DaveL59]

thinking a bit more on this, you might be able to determine which side to best adjust by alternately closing one eye and see which side seems the most offset (or keep both eyes open and cover/uncover one objective at a time)

[Alan64]

I'd hate to think for even a moment that you damaged the alignment of your eyes due to said injury.

I've read your introduction, and found that you prefer binoculars to telescopes.  I am the exact opposite, as I have three pairs of binoculars myself, but I rarely if ever use them, either during the day or night.

In any event, I do hope that that pair of binoculars is defective, as that will mean your eyes are not.  

[richard5700]

Hi.  What I thought I would do, is do the simplest thing, which was to turn the right hand objective barrel and see what happens. Well, I found that by unscrewing the barrel about 10 degrees, I achieved an alignment sufficient to produce a single image of a star. Of course, that leaves the barrel loose and it upsets the factory set collimation. After a spell of night sky viewing, I simply re-tightened the barrel.  Seems a reasonable solution in this case. But if I had very expensive binoculars possibly not.

Edited September 1, 2019 by richard5700

[DaveL59]

at least that's a fairly easy result, you may be able to improve the barrel "tightness" by adding some sort of gasket to keep it all stable. Something like sugru eased into the gap might work if you unscrew a little further and lay a thin segment round and retighten, or even a turn of ptfe tape on the thread may do it.

If you do want to get a more expensive pair, an optical shop that does bino repair may be able to sort an offset adjustment to suit, assuming there's a good target to use and you present to test with them of course. Would likely affect warranty tho...