# Do eye-glasses decrease the Depth of focus?

I was reading up about Depth of Focus and wondered if glasses affect depth of focus. If yes, is it noticeable to the user?

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This is very much like the concept of depth of field in photography. The wikipedia article is here. Changing the focal length of the lens changes depth of field, but it is only noticeable for large changes. –  Fingolfin Oct 23 '11 at 5:37
I think this probably depends on your preferred definition of depth of field. I'm nearsighted, so I could say that without glasses, my depth of field, measured as a length, is about 1 meter. Looking through the tops of my bifocals, I can see stars that are ten light-years away, and I can also comfortably focus as close as about 2 meters. Does this mean that my depth of field improved by some gigantic factor? Well, maybe, but it sort of depends on how you define it. –  Ben Crowell Sep 14 '14 at 16:49
It might actually be more natural to measure depth of field in terms of $\Delta(1/x)$ rather than $\Delta x$. –  Ben Crowell Sep 14 '14 at 17:19

Depth of focus is most strongly affected by the pupil size--- when the pupil is very constricted, the depth of focus is large, and when the pupil is dilated, it is narrow. The effect is most obvious in the extreme case of a lensless pinhole camera.

The eyeglasses simply change the location of the focal point for a given tension in the eye's lens, and the effect on depth of focus is negligible, I believe.

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Depth of field is related to aperture in a way you can understand with these diagrams. Are common glasses reducing aperture as a diaphragm do, for example, in photography? You can think of the lens in that diagrams as your eye pupil. The frame of your glasses is wider than it, so the limiting element is your eye entrance.

Anyway decreasing aperture will enlage DoF! That is why pinhole camera pictures focus at every distance. You can try some things looking through a pinhole, as I point out in the link.

Edit: I understood your question as pointing to aperture and not to focal length...

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