Impaired binocular vision? exit pupil problem?

[Alfian]

I have been having a problem using my 10x50 binoculars. Wearing specs' I couldn't quite get the views I wanted and had put it down to the marginal eye relief. I'd had an eye test and a new prescription, but the optician wanted an opthalmologist to check my eyes with respect to a scar he had found on my left eye. Given that I didn't feel to have any problems and that my eyes were "healthy" I thought he was perhaps just being a bit over cautious.

After the usual long-ish  wait for an appointment I visited the opthalmologist yesterday, who with effeciency and a slightly over clinical manner revealed that I had indeed got a small healed scar on my left eyeball which she didn't think would affect my general vision (which I don't think it has generally) and could see no reason to take the matter any further. Discharged. Fine, a  storm in a tea cup. Yes, the optician was just being cautious.  Then of course, once the sting and the ache in my eyes from the eye drops to dilate my pupils and more to anaesthetise my cornea,  had worn off, I gets to thinking why didn't I ask where this little scar was?

It has occurred to me that if the scar is off centre then perhaps with a normal 2-3mm exit it indeed would not be an issue, with a wider exit in dim light for normal purposes (ie not astronomical observation!) it would probably also not be an issue. Maybe though when you are deliberately trying to get as clear an image as you can with a 5mm (ish) exit pupil, as in looking through an eyepiece, it might be a problem.  Part of my reasoning here is that I don't have a perceived issue with my Pentax20x60s which have a 3mm exit  and possibly when using my 6.5 x32s which give a much wider less contrasty view, I'm not  being quite so picky in terms of the detail I expect to see. Perhaps I'm trying to make the facts fit the theory!

I suppose, that's my question and its the one I should have asked yesterday, if there are any astronomers out there who are also optometrists, is that conclusion a possibility?

If I am correct in my assumptions then any binocular purchased in the future will have to have to have a smaller exit - but how small? Perhaps I do need to have a another word with my optician!

Incidentally  after initially dismissing the notions of the optician that I'd had an accident involving my eye, I remembered, digging deep, that earlier this year when working in the garden a blade of grass caught my eye, making it  really water, in fact for a day or two it was a bit of problem, but then it was OK , it was fine, all forgotten about.  There's a lesson there somewhere.

 

Apologies, meant to put this in the Astro Lounge! Where are my glasses?

 

 

 

[billyharris72]

Not an optometrist, but this seems unlikely. As the exit pupil increases (assuming your pupils are dilated) you'll be getting the sort light input to the eye that you would be under normal circumstances, where there does not seem to be a problem. Also, assuming the problem is relatively minor, your eyes should do a prety good job of compensating.

I'm not an optometrist though, so why not test it further? A couple of things come to mind.

1) What kind of views do you get when you close one eye and just use the other? If the views are both decent then it's probbaly collimation.

2) If your "bad" eye does have a worse view, what about trying a telescope with that eye and a 5mm exit pupil? That could help to rule out any other problems effecting that part of the binocular.

If, in both tests, the "bad" eye really is worse then another visit to the optician might well be on order.

Billy.

[Astrobits]

Apart from the suggestions from Billy, why not take your binoculars along to your normal/nearest astronomy group, there might be someone there that can assess your bins. Alternatively,  The Amateur Astronomy Centre in Todmorden. Peter Drew at the AAC  will be able to tell you if the bins are faulty.

Nigel

[Alfian]

Hi and thanks for the response. I think I have pretty much resolved the issues, at least  in terms of being settles in my mind about things.

I found there was a minor issue with the bino. The L/H eyepiece  eye-cup had come partially unscrewed, but was not loose, making the somewhat marginal eye relief even more so on that side. I think this might account for the odd feel to things.  The collimation of the WOs  as far as I could test them  hands free on a  tripod is spot on.  As to my eyesight, I have had a very mild astigmatism in my left eye as well as myopia. The latter isn't a problem as this focuses out, the former  has not been much more than an irritation that I can put up with to some extent choosing to use binos without specs as it so  much more comfortable. That astigmatism has been "stable" for many years, but it has changed in more recent times to the point where I now really do need to use my specs.  Add to this the damage issue that the opthalmologist  wanted to look at, and I was wondering whether a smaller exit would help, especially given that my Pentax 20x60s with the 3mm exit seem fine to use.

I think the bottom line here was coming to terms with changing eyesight and the need to use specs' for observing. The marginal eye relief of the WO 10x50s together with its little imbalance, now corrected, served to emphasise this. I think a reduced exit possibly does help as well.

I have just purchased an Opticron iMagic 10x42, which is a nice little binocular. It has very good eye relief and I have not had a problem with them so far, though time under the stars has been limited.

I have annual tests which come around too quickly so I shall no doubt keep myself appraised of the state of my eyes.