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binocular overlap

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Old Friday 5th January 2018, 09:10   #1
chris6
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binocular overlap

It was raining so, indoors, did another comparison within my collection, where I have also previously seen semi-circles on either side towards the sides of the view. In each set of binoculars this was present to some degree and seemed to be an overlap between the views with either eye rather than something wrong, although I did not fully understand it.

This was usefully confirmed and explained in an old thread here:
http://www.birdforum.net/showthread....hlight=overlap
and elsewhere at:
http://vrguy.blogspot.co.uk/2013/05/...p-and-why.html
- so thought it might be worth mentioning again.
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Old Friday 5th January 2018, 10:43   #2
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This is normal Chris. At very close distances the fields of view of each of the optical tubes of your binos do not overlap fully so you see a field in the middle where the fields do overlap and then to each side a crescent-shaped field that is the field seen by only the single tube on each side. As the distance to what you are looking at increases, so more of the two fields of view overlap until a point where the overlap is total and there is just the big circular field that we all expect, providing we have set the inter-pupillary distance correctly.

When using the close-focus capability of binos this splitting of the view into crescent/overlap/crescent can be distracting and by closing up the bino hinge a bit (reducing the IPD) you can reduce this effect but actually if you concentrate on the subject you are looking at it is possible to ignore the distractions of the 'split' field of view. I say that it is possible but this might be a trick that not everyone is comfortable with, like not everyone can look through a scope with both eyes open and just concentrate on the view coming through the scope.

Hope this helps.

Lee
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Old Friday 5th January 2018, 12:23   #3
chris6
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Lee, thank you for your advice, it is just as you said. In a fresh bout of obsession with binoculars I have been comparing them indoors, which evidently makes it more obvious.

I blame the comments and recommendations in this forum for causing yet another acquisition, Eden XP 10x56. These have just been delivered and, once I have looked them over a bit more, will post about them too.

Last edited by chris6 : Friday 5th January 2018 at 12:43.
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Old Friday 5th January 2018, 12:49   #4
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Quote:
Originally Posted by chris6 View Post
Lee, thank you for your advice, it is just as you said. In a fresh bout of obsession with binoculars I have been comparing them indoors, which evidently makes it more obvious.

I blame the comments and recommendations in this forum for causing yet another acquisition, Eden XP 10x56. These have just been delivered and, once I have looked them over a bit more, will post about them too.
Look forward to hearing about them Chris. As an aside, it is better to set the dioptre on new binos at your normal viewing distances rather than the super close distances inside your house.

Lee
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Old Friday 5th January 2018, 17:50   #5
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Right Lee thanks. Just in case it mattered, I have got used initially to checking this both ways, and apart from the odd Bushnell , for me, with updated glasses they have seemed to be ok at zero.

I have reckoned that my glasses (meaning 'spectacles') have put me to zero and that has solved the problem. The glasses have themselves been a nuisance, simply because "eye relief" is often quoted so imprecisely. Anyway crude testing has indicated that using my glasses has helped a lot, presumably because of astigmatism so that, at least for me, this is the way to go.

Unfortunately, although my lovely recently acquired vintage 8x30 WA Avocets have roll-down eye cups it is not nearly enough. They are already plenty sharp without it so it would be nice to see what they would be be like with correction for that particular type of refractive error. To me it has been interesting both to see how much the Avocets need good light to perform, and that otherwise their (early?) coatings seem to be able to handle things very well. Perhaps they were especially good even then, or perhaps sharpness and CA were not so much of a problem before the 'roof prism' takeover.

From various comments it has seemed to me that, since then, it has been light transmission as well as control of CA (apparently not so critical with porros) which may have become more important, even than sharpness.

Clearly porros can still rule, SE 8x32, and i.m.o. even still be good at very reasonable cost with Celestron 7x35, but I just don't like the idea of the eyepieces wobbling around on a stalk, or the stiff focus action which seems to be required to waterproof the latter.

With porros I have often tried moving them individually by hand and found that it made no difference, while images of broken bridges have certainly made an impression. May I ask what else might Not be Happening (to change focus) when each eyepiece is moved individually by hand? Is it just that the eyes accomodate to match the altered binocular relationship?

I guess that 'waterproof' is largely a marketting/subjective thing: how often do I go out at all? (rhetorical)....let alone how often do many others wander about in the rain? Anyway the focussing action of waterproof porros seems (in my limited experience) to introduce unacceptable friction and stiffness.

If the eyepieces were to be outside the volume which has been 'nitrogen purged' (roofs?) while something (?) else is moved, this would not be a problem. However I have somewhere seen reference to pumping action when porro eyepieces are moved, so how is this accommodated please? Is it just a question of greased O rings on the eyepiece tubes? ...surely not, or maybe that's why porros are not the thing i.e. because they can't really be made waterproof?

Last edited by chris6 : Friday 5th January 2018 at 20:48. Reason: correction
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Old Saturday 6th January 2018, 08:28   #6
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We all speak based on our own experience and often believe that it is the same for everybody and I am as guilty of that as anyone. So it always surprises me when anyone says something along the lines of 'is waterproofing really necessary when hardly anybody stands outside in the rain'. I hope I haven't misrepresented what you posted there.

At home, if its raining, I generally don't say 'lets go out for a walk' but on holiday its different. We mostly go to the west of Scotland and especially the islands and we can set off over the hills and coasts in glorious sunshine and then the clouds open up and dump rain. Our car or cottage might be miles away and even if it is raining there can appear eagles, divers, otters, seals, falcons etc etc at any time. We don't put our binos in our backpacks. OK, you say, serves you right for going to the west of Scotland, but doesn't it apply elsewhere too?

Take Suffolk. If it rains at RSPB Minsmere you are probably 5 minutes maximum from hide where you can shelter, but if you are a few miles away on the marshes at Walberswick it could be an hour before you reach shelter. So you can see why we are grateful for waterproof binos and shudder at the memory of Swift porros in the 1970s that fogged up after every shower on the North York Moors and needed to be sent back to the importer after every holiday to be dried out. We didn't understand that these centre-focus porros were not waterproof and were so glad to get our Zeiss and Leica roofs that were.

My Zeiss Dialyt 10x40 BGAs focussed by moving the objective lenses so in principal they had similarities with the centre-focussing Swift porros but they never fogged. On the other hand the moving objectives did act like a pump and although they never let any dust in past the objective seals, when I used them up in an airliner with reduced air pressure the pump action could be felt through the focus wheel. Clearly the objective seal was not consistent in its gas sealing effect because as I focused sometimes there was a lack of resistance and then suddenly there was an increase in resistance which I put down to the gas-sealing letting go and then making good. The objective seals were grease lubricated so as the lenses moved back and forth I am guessing this grease layer sometimes made the bins gas-tight and at other times this didn't work. Back on the ground there was never any sensation of pumping of variation in focus effort required.

Lee
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Old Saturday 6th January 2018, 08:47   #7
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Lee

Of course you are right, and I must try to get a grip. I can see that roofs are essential for serious hiking and birdwatching and admit that I prefer them too, if only in case I forget about them and leave them out in the garden, which happens quite often
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