Focusing for relaxed eyes (1 Viewer)

To keep yourself from accidentally focusing with eye strain,
I have found this trick "relaxing":

----focus on something closer than your target (approximate focus)
----now focus on something beyond
---note the direction you had to move

---now slowly pull the focus back (from far) to clear up your target...
stop when it just looks sharp

This puts your eye muscles in the relaxed 'infinity' position so you
can stare longer without strain. The same applies to doing diopter
adjustment...even moreso.

Way back in the 1970's when I bought my first Zeiss Dialyt, the instruction booklet advocated something similar.

It advised that you should roll the focuser so that the point of focus went past the object of interest and that you should then smoothly reverse the direction of focus and stop when your object is sharp. In this case the suggested initial direction of focus was from far to near, followed by a final move from near to your object.

Lee

Troubador said:

Way back in the 1970's when I bought my first Zeiss Dialyt, the instruction booklet advocated something similar.

It advised that you should roll the focuser so that the point of focus went past the object of interest and that you should then smoothly reverse the direction of focus and stop when your object is sharp. In this case the suggested initial direction of focus was from far to near, followed by a final move from near to your object.

Lee

Click to expand...

Lee, I remember something similar.

By gosh I do remember something from the 70's! : )

Anyway I tend to work my binocular in that fashion.

Bryce...

This sounds very counter-intuitive to me, being myope and optician. If the binoculars are focused to an object at a distance like say 10 meters, the eyes have no chance to relax so that objects further away become sharp.

I'd advocate the opposite: Focus closer than the object and dial in the focus from closer to further. This means that the accommodation effort is at its minimum but the perceived depth of field might suffer from this if you're young.

//L

The problem is, your eyes can get something into perfect "close focus" without
you realizing the muscles are under tension. (you can focus your eyes paerfectly
over a certain range).

If you achieve 'good focus under tension', it will only dawn on you over a few minutes
as the muscles fatigue and let the diopter value of the eyes slip. When you focus as
though you were looking at infinity (or the long limit of the unaided eye), there is
no muscle tension left and the eye can maintain that indefinitely.

OPTIC_NUT said:

To keep yourself from accidentally focusing with eye strain,
I have found this trick "relaxing":

----focus on something closer than your target (approximate focus)
----now focus on something beyond
---note the direction you had to move

---now slowly pull the focus back (from far) to clear up your target...
stop when it just looks sharp

This puts your eye muscles in the relaxed 'infinity' position so you
can stare longer without strain. The same applies to doing diopter
adjustment...even moreso.

Click to expand...

This approach for relaxed eyes doesn't make sense to me either, nor does it match with my experience. If bins are focused beyond the object, or beyond infinity, the eyes will use accommodation to correct the focus (i.e. will not be relaxed). If, instead, the bins are focused in front of the object, the eyes relax to achieve best possible focus under the circumstances. If the focus is then refined to perfection by slow adjustment from near to far, the eyes should be be relaxed. Your procedure seems better for a different purpose: maximizing apparent depth of field for a person with good accommodation ability using a binocular with a curved field (but with little astigmatism). Focus in the center will be achieved using accommodation (eyes not relaxed) and will be achieved off center by relaxing the eyes.

--AP

I agree with LS and Alexis. For an object at a given distance, there is a range of focus settings and a corresponding range of muscular accommodations that will give a sharp image.

The virtual image is brought closer at the focus settings for further away. That situation requires accomodation however, and if overdone results in eyestrain.

The most relaxed condition for the eye muscles is for the virtual image to be at infinity, or for a myope, beyond the distance of sharp viewing. So it seems to me that starting with the focus set too close puts the eyes in their most relaxed state, and when the focus is finally set far away enough to looksharpe, and you stop right there, the eyes never strain.

There is however a natural tendency, when straining to see detail, to position the virtual image as close as possible, because the magnification is a little greater that way. But you will wear your eyes out fast like that, as planetary observers soon learn.

Ron

Sounds like most of us are agreeing with the method Zeiss advocated all those years ago.

I wonder why they stopped giving this advice?

Lee

Troubador said:

Sounds like most of us are agreeing with the method Zeiss advocated all those years ago.

I wonder why they stopped giving this advice?

Lee

Click to expand...

It may depend on their presumed audience.
When it was originally written, people newly to binoculars with a sudden
flush of money could have been the target. If the market is mostly
fanatics with prior experience, the instructions might not be read.

Still, someone could go many years without realizing the best practices.
Eyestrain down the drain.
There should be a "basics of binoculars" book/booklet.
How to pick, adjust, clean, hold, etc...
A 24 page version blurb, not much on the internal lore.
I do a broadsheet giveaway for my bookshelf at the antique shop...
mainly what the numbers mean, what uses vs. sizes and types, etc...
There have been many takers. People start out on the chopped/monoculars
often. Less intimidation. Just the diopter business baffles many. Funny,
they can whip through a couple dozen keystrokes to get a number on
their phone. "Real" things shock them. Someone told me the view
"was too real".