To Infinity, and Beyond (1 Viewer)

Dr Owl · Feb 1, 2015

Good afternoon everyone,

Can binoculars focus closer if I wear reading glasses?

Let me explain. Many binoculars focus beyond infinity if a person with “normal” vision racks them right in. This, I understand, is so that folk with short sight, who have no astigmatism and a relatively moderate prescription, can use the binoculars without eye glasses ... and without having to worry about how much eye relief the binoculars offer.

So, in turning the focusing wheel from their infinity to the closest possible setting, short-sighted folk turn the focusing wheel just a little more than normal-sighted folk. Surely this should mean (he said hopefully rather than confidently) that they focus just a little closer?

Personally, I cannot get the best out of binoculars without my eye glasses: I have a prescription of -9 dioptres, and significant astigmatism. (This makes me neurotic about eye relief for cameras and binoculars.)

And, like everyone else, in middle age, I have lost close focus; and need a different, less negative, prescription for reading. I have a pair of single-vision reading glasses with +2.75 dioptres over my base prescription (ie a total of -6.25 dioptres).

Would our original-EL 8.5x42 Swarovskis focus closer if I wore these reading glasses?

(You may be wondering why I just don’t go out into the back garden and experiment? It’s like this: I took all three pairs of Owl and Pussycat binoculars to our son’s house to show our embryonic-astronomer ten-year-old grandson. He was thrilled to be given a pair of standard-grade 10x50 Nikons. Big sister (14 going on 30) tried them all, decided the Swarovskis were the best, and “borrowed” them. They haven’t come back yet: other grandparents will understand.)

Later

Dr Owl

----------------------------
John Owlett, Southampton, UK

Troubador · Feb 1, 2015

Dr Owl said:
Good afternoon everyone,

Can binoculars focus closer if I wear reading glasses?

Let me explain. Many binoculars focus beyond infinity if a person with “normal” vision racks them right in. This, I understand, is so that folk with short sight, who have no astigmatism and a relatively moderate prescription, can use the binoculars without eye glasses ... and without having to worry about how much eye relief the binoculars offer.

So, in turning the focusing wheel from their infinity to the closest possible setting, short-sighted folk turn the focusing wheel just a little more than normal-sighted folk. Surely this should mean (he said hopefully rather than confidently) that they focus just a little closer?

Personally, I cannot get the best out of binoculars without my eye glasses: I have a prescription of -9 dioptres, and significant astigmatism. (This makes me neurotic about eye relief for cameras and binoculars.)

And, like everyone else, in middle age, I have lost close focus; and need a different, less negative, prescription for reading. I have a pair of single-vision reading glasses with +2.75 dioptres over my base prescription (ie a total of -6.25 dioptres).

Would our original-EL 8.5x42 Swarovskis focus closer if I wore these reading glasses?

(You may be wondering why I just don’t go out into the back garden and experiment? It’s like this: I took all three pairs of Owl and Pussycat binoculars to our son’s house to show our embryonic-astronomer ten-year-old grandson. He was thrilled to be given a pair of standard-grade 10x50 Nikons. Big sister (14 going on 30) tried them all, decided the Swarovskis were the best, and “borrowed” them. They haven’t come back yet: other grandparents will understand.)

Later

Dr Owl

----------------------------
John Owlett, Southampton, UK

John

My bins work at close focus just fine with my varifocals, looking through the long distance section.

Thing is, if you were to wear you reading specs you would have a tough time spotting and following those pesky butterflies and dragonflies that are just a few paces away.

Lee

Binastro · Feb 1, 2015

. Dear John,
. The magnification of the binocular may also change if you wear glasses, and possibly without glasses.

I am longsighted and can use spectacles to increase the magnification.

I'm not sure if the field of view varies also.

Alexis Powell · Feb 1, 2015

Dr Owl said:
...Would our original-EL 8.5x42 Swarovskis focus closer if I wore these reading glasses...

Yes.

--AP

kabsetz · Feb 1, 2015

The answer is yes, but not by much. +2.75 is a little more than what my glasses have, and in the quick and dirty comparison I just did with a 10x42 that focuses to a little over 2 meters, the difference in distance between no glasses and glasses was less than 5cm. This was not a rigorous test, but the result should be in the right ballpark.

Kimmo

WJC · Feb 2, 2015

How does a binocular focus "beyond" infinity? I thought infinity was . . . infinite!

OPTIC_NUT · Feb 2, 2015

kabsetz said:
The answer is yes, but not by much. +2.75 is a little more than what my glasses have, and in the quick and dirty comparison I just did with a 10x42 that focuses to a little over 2 meters, the difference in distance between no glasses and glasses was less than 5cm. This was not a rigorous test, but the result should be in the right ballpark.

Kimmo

Makes sense. The diopters of the eyepiece are so much stronger.
If you really want to focus closer, take a page from the camera book:
a 0.25D or 0.5D camera closeup lens makes a huge difference in the
nearpoint...when put in front of the objective.
The view will be out of alignment, of course. So you apply that
to just one side and use it as a minocular. I've done that. It's fun.

Dr Owl · Feb 2, 2015

Thank you everyone.

Alexis Powell said:
Yes.

kabsetz said:
The answer is yes, but not by much. +2.75 is a little more than what my glasses have, and in the quick and dirty comparison I just did with a 10x42 that focuses to a little over 2 meters, the difference in distance between no glasses and glasses was less than 5cm. This was not a rigorous test, but the result should be in the right ballpark.

Thank you for confirming that my optical ramblings were valid ... even if they are of no practical benefit. I wasn't sure: I have no training in optics beyond sixth form (high school) but have learnt to apply these principles to photography. Light is still light (even if I don't believe in photons) so the same principles should work for binocular systems, but I realize that I'm starting again.

Troubador said:
My bins work at close focus just fine with my varifocals, looking through the long distance section.

Thing is, if you were to wear you reading specs you would have a tough time spotting and following those pesky butterflies and dragonflies that are just a few paces away.

You're right of course: it would be a pain to have to swap outdoor varifocals and reading glasses between sighting a butterfly and closing up on it. But I would so much prefer to carry a single pair of do-everything binoculars -- which may not exist -- and I usually have reading glasses in a jacket pocket.

Though swapping is not worth doing if all it gains is 5cm or so.

Binastro said:
The magnification of the binocular may also change if you wear glasses, and possibly without glasses.

I am longsighted and can use spectacles to increase the magnification.

I'm not sure if the field of view varies also.

Good point. I'd forgotten that if you change one part of an optical system, you affect everything.

And I've known for half a century that my short-sight eye glasses reduce the size of what I'm looking at, as well as sharpening the image enormously.

WJC said:
How does a binocular focus "beyond" infinity? I thought infinity was . . . infinite!

You're asking someone who learns his astrophysics from Buzz Lightyear? :eek!:

My theory is that it is caused by quantitative easing. Because of a fear of deflation, which would crash our weather balloons (o)< and make us unable to predict snowstorms reliably, the Bank of England and the Federal Reserve go in for this financial engineering which ensures continued inflation. This means that infinity is larger than it was.

In fact there are infinitely many different infinities of different sizes, so mathematicians have to use unramified forcing to keep them all under control ... but this has absolutely no significance for geometrical optics. :h?:

Later,

Dr Owl

----------------------------------
John Owlett, Southampton, UK

Troubador · Feb 3, 2015

Dr Owl said:
financial engineering which ensures continued inflation. This means that infinity is larger than it was.

In fact there are infinitely many different infinities of different sizes, so mathematicians have to use unramified forcing to keep them all under control ... but this has absolutely no significance for geometrical optics. :h?:
Dr Owl
----------------------------------
John Owlett, Southampton, UK

John

This is a common misconception. There is only one infinity and it is of fixed size because clearly it can't be any larger and it cannot be smaller or it would not be infinite. However, being the same size as ever it was, since everything else has been subject to inflation for millenia, infinity has got more crowded and there is not as much room left in it as there used to be. In this sense (and in this sense only) infinity is now smaller.

Euclidian geometry has, unnoticed by mortals, changed over the centuries due to this progressive crowding of infinity. The effect has been that one can no longer have right-angled triangles with the astronomically long hypoteneuses that Pythagoras imagined, as there is no longer enough room for them. QED.

Still the universe is fascinating optically. For example, the next time you are on the summit of Everest, you will find that it's field of view is an infinite number of metres wide from only 1 cm in front of your face! Amazing. Although the edges are not as sharp as we would like. Still, there are other objects of interest, like the lensing-galaxies, known by some as Zeiss Galaxies, which produce up to more than one image of the interstellar objects hidden behind them.

Sorry, what was the question?

Lee

brocknroller · Feb 10, 2015

WJC said:
How does a binocular focus "beyond" infinity? I thought infinity was . . . infinite!

It all depends on whether the universe is flat, open or negatively curved. :smoke:

Of course, being an old pro, you know that every bin's focuser turns a bit beyond closest focus and a bit beyond farthest focus, how far depends on how many diopters the right EP has. I knew my 7x36 ED2 was failing when the focus beyond "infinity" began to shrink until there was none left. At first, I thought the universe might be collapsing back on itself, but then I figured out that the diopter was drifting...

<B>

OPTIC_NUT · Feb 10, 2015

"
thought the universe might be collapsing back on itself, but then I figured out that the diopter was drifting...
"
Good God! Scary moment. Carlos Castenada described such moments after consuming Datura.
heh..

So the latest/greatest theory is.....our Universe is just one of many and its bits will expand
but be pulled to join other bang-leftovers from other universes to join up and make
another bang made out of those leftovers, etec. etc.... a "foam" or universes.

At that isn't even the extra - dimensional scene where the other gravity poles are stashed in another
universe-plane somewhere else.

To Infinity, and Beyond (1 Viewer)

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Dr Owl

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Binastro

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