Understanding diopter adjustment (1 Viewer)

I ran into this dilemma. Having pretty poor eyesight, I am forced to adjust the diopters but cannot quite get them as nicely adjusted as well as when I am wearing glasses.

And when wearing glasses, the diopter settings are different, but the picture is slightly more crisp.

Now this question - there is a display of the diopter setting, but what does it show? The right one or the left lense? I do understand that the top wheel controls the right lense and the bottom, the left. But it seems there isn't a display for the left lense?

You eyes probably have some astigmatism, which is why you get a better image with your glasses. I never use my binos without my glasses on for this reason.

The diopter setting shows the adjustment of the right side. The left side adjustment is coupled to zero on the scale, so it doesn't matter which wheel you turn, you'll get the same correction at a given setting on the scale.
--AP

I probably do have minor astigmatism, I need to check this.

Without glasses I cannot bring my left eye to focus at infinity, but the right eye is OK. For the left eye, it seems like I need the focusing wheel to travel forward another few millimeters after it bumps against the body of the binocular.

It's very close to focus but not quite.

The diopter setting is set to -1.3 units on the scale, whatever that means.

The focus is sharper with glasses. With glasses, I am in the + territory, forget exactly where.

Alexis Powell said:

The left side adjustment is coupled to zero on the scale, so it doesn't matter which wheel you turn, you'll get the same correction at a given setting on the scale.
--AP

Click to expand...

I don't understand the above. Are you saying that you can only adjust the diopter for one eye? Why then we have 2 focusing wheels? And why can't I adjust both of them, just one?

You do have 2 focusing wheels but one of them is for use with both eyes. The diopter focusing wheel is for your right eye only. Once you set it for your right eye you forget about it. Here is how I set mine. (I have a binocular that locks the setting of the right eye.) I set my left eye first. Using the center focus wheel and WITH MY RIGHT EYE SHUT I focus the left eye on a telephone pole that is about 400' distant from my deck There are letters and numbers painted on the pole that I use to determine the sharpness of the focus, once these are sharp I take my finger off the focusing wheel, THEN I CLOSE MY LEFT EYE and using the diopter wheel I focus for sharpness on the letters and numbers with my right eye, when they are sharp I then open both eyes and GENTLY fine tune the focus using the Center Focus wheel until I get a nice sharp image with both eyes open and then I lock the right eye diopter. The binocular here is a 7 x 42 BN Trinovid. I haven't had to reset it in months.

Cordially,
Bob

If your right eye focuses properly, but the left won't, it seems you either haven't set the diopter correctly, and/or you're running up against the bino's combined focus/diopter correction limit. I think the BN only allows a maximum of -4 diopters beyond infinity and that this is equivalent to its maximum 4 diopters of focus correction. The little raised circular bump next to the diopter readout will line up with a little triangular arrow molded into the bino armor on the left side when your eyes are perfect (or are properly corrected) and the bino is set at infinity. So if, without glasses, your right eye needs -2 correction and your left eye needs -5 correction, you won't be able to adjust the diopter to correct the focus of your left eye for infinity (when you aren't wearing glasses), because -2 diopters are being used up to correct the right eye, leaving only another 2 diopters to adjust the left eye though 3 are needed. I hope I thought this through and wrote this correctly!

The procedure that Bob gave will work to properly set the diopter, and is basically the same procedure that is used to set the diopter on any bino. But Leica binoculars (unlike other brands with integrated central focus/diopter adjustment) completely decouple the left and right side focus when the top and bottom parts of the focus knob are seperated. The top portion with the diopter scale changes the right side focus, and the bottom portion (which Bob incorrectly refers to as the central focus knob) will adjust the left side focus. As a consequence, after pulling apart the focus knob, you can adjust the diopter (relative focus of the left and right sides) by adjusting the focus of either the left or the right side of the binocular first, or even switch back and forth--it makes no difference. Once both sides are focused properly on a very distant object, lock the setting by snapping the two portions back together.

There is only one diopter scale needed because it shows the difference of the right side focus relative to the left side (the left side focus establishes where "0" is). So let's say your right eye needs a diopter adjustment of +1 relative to the left side. If you followed Bob's procedure, you would focus the left side first (so "0" would correspond to infinity focus). Then you would focus the right side to the +1 setting to bring it into focus. Alternatively, you could set the right side focus first (and the diopter might perhaps read "0"). Then , when you adjust the left side to -1 diopters to bring it into proper focus, the zero of the scale will move so that teh dial reads +1, which is the adjustment of the right relative to the left (equivalent to setting -1 on the left side).

If you have the correct glasses prescription, they will provide you both the proper diopter correction AND will correct your astigmatism. In that case, the only reason for setting the diopter is to correct for the slight miscallibration of the diopter scale (very common for it to have to be set slightly off the zero mark, though mine are perfect in this respect).

Bob mentioned closing each eye alterately--I recommend that you instead cover the objectives instead. Closing an eye causes squinting and pupil constriction and generally throws off your most relaxed left/right natural balance (imbalance) a bit. Bob's touch-up phase with both eyes open allows him to correct for this.

--AP

.... then I lock the right eye diopter. .


do you start with the diopter unlocked and keep it unlocked the whole time?



... or you're running up against the bino's combined focus/diopter correction limit.

That's it, I have something like -5.5/5.25 diopter vision. 4 diopters that 8x42BA offers is not enough apparently.

When I focus the left side, I immediately run out of room. The wheel (the bottom piece) needs to keep turning more but it stops. In fact, I don't get crisp focus with the left eye no matter which side I try to focus first.

etc said:

.... then I lock the right eye diopter. .


do you start with the diopter unlocked and keep it unlocked the whole time?



... or you're running up against the bino's combined focus/diopter correction limit.

That's it, I have something like -5.5/5.25 diopter vision. 4 diopters that 8x42BA offers is not enough apparently.

When I focus the left side, I immediately run out of room. The wheel (the bottom piece) needs to keep turning more but it stops. In fact, I don't get crisp focus with the left eye no matter which side I try to focus first.

Click to expand...

ETC
I keep the right diopter locked until I have focused my left eye. (Sorry I didn't make that clear.) THEN I unlock the right diopter wheel and focus the right eye, and then, as I noted, I fine focus with both eyes open using the bottom wheel and then lock the right (top wheel) diopter. (I note that you are using a Trinovid or Ultravid binocular.)

AP explains why there isn't enough focusing room for your left eye. You can test it yourself by trying to set your diopter while wearing and not wearing your glasses. Pick something about 400 feet away to focus on like I do. Note that I am setting my focus on an object 400 feet away, more or less, and that my binocular still has focusing room beyond that, but I rarely extend
it further. (For all practical purposes 400' is infinity with my binocular.) Can you get sharp focus from your binocular in your left eye while wearing your glasses? At any distance; close, medium or long range? If you can, then it is not likely a problem with your binocular or your focusing technique and you may be required to wear glasses to get a sharp view with your left eye.

Bob

..... Can you get sharp focus from your binocular in your left eye while wearing your glasses?


Yes... and cannot without, no matter what I do. Starting with the left unit (bottom focusing wheel), whether the top diopter wheel is locked or unlocked, the picture is not quite clear,not as sharp as when using glasses.