I often remove my sunglasses in flight. It does significantly increase my
ability to see details both near and far.
One reason is that the eye's pupil works just like the f-stop in a camera
lens. The smaller the opening the greater the depth of field. With
sunglasses the pupil opens wider and reduces the depth of field. Older
pilots like me find that a large depth of field compensates somewhat for
presbyopia making PDA's easier to read.

Another reason is that few human corneas are perfect. A small pupil opening
reduces the area of cornea surface used to form an image on the retina
increasing the sharpness of the image.

Yet another reason is that any optical surface where light passes from one
refractive index to another, like the surface of sunglass lens where the
light goes from air to plastic, reduces the light intensity and contrast by
about 4% in addition to any tinting. The lens actually has two optical
surfaces, one is the front surface and the other the rear surface. There
are other effects like internal reflections within the sunglass lens that
reduce acuity.

I always wear wrap-around sunglasses on the airfield, both to protect my
eyes from the sun and to protect them from the high velocity grit kicked up
by tow planes. Any time you are in the vicinity of a turning propeller,
ballistic eye protection is a must.


Bill Daniels


"kirk.stant" wrote in message
oups.com...

Tim Taylor wrote:
Ray,

The answer is probably not because we wear sunglasses while I am
guessing the participants in the study did not.

Tim

Well that begs the question: Is it better to wear sunglasses (knowing
that you are reducing the amount of light your eyes are seeing,
therefore possibly reducing visual detection range) or no sunglasses
and black anti-glare face paint?

I know of some old fighter pilots who swore by not wearing sunglasses
or colored visors - instead they squinted. Since it was a life or
death situation, I have to think they might have been on to something.

I just got through a season wearing non-tinted prescription glasses
(instead of my usual sunglasses) and find I did not miss the sunglasses
much - and found vis under clouds much better (also the PDA is easier
to see).

Now I may have to stop by the sports store and get some anti-glare
paint - and really freak out the twirlybirds at the local glider club -
to say nothing of the crowd at a contest!

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