# How do a microscope's optics expose defects in the user's vision?

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I've got cataracts in both eyes. My vision is correctable to 20/30, so the cataracts are essentially a non-issue in daily living. But when I use a microscope, which I do daily, (binocular, zoom 7x-30x) the picture I see is occluded in the area where the cataracts are on the lenses of my eyes. I can sort of see the shape of my cataracts by using the microscope. What is it about a microscope's design that makes viewing much more difficult than with ordinary vision?

This post imported from StackExchange Physics at 2015-05-15 23:44 (UTC), posted by SE-user Lenny

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My intuition is that normally your eye collects light from a large area to form an image, so small-ish obstructions like cataracts get "blurred over" whereas when looking through a microscope the image is coming from a very small area and the light acts as the bulb in a projector, with your cataracts as the projected "slides" and your retinas the "screen."

This post imported from StackExchange Physics at 2015-05-15 23:44 (UTC), posted by SE-user Asher
answered May 9, 2015 by (20 points)
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When looking with the unaided eye, light from a single point object reaches all parts of the lens and is focused back onto a single point on the retina. Light from all points on the lens reaches all point on the retina. Point defects on the lens affect the quality of the entire image rather than specific parts of it. Occlusions on or near the lens are equivalunt to using a smaller lens. They predominatly make the image on the retina dimmer and fuzzier.

When optical instruments are used they do most of the focusing. The light reaching your lenses is already prefocused. The light going to a single point of your retina then only goes throgh a small part of the lens. Point defects on the lens only affect small parts of the image and occlusions on the lens actually block corresponding parts of the image.

This can be worked out usig ray diagrams A Wolfram interactive demonstration of microscope ray diagrams can be found here. There is also a youtube video

This post imported from StackExchange Physics at 2015-05-15 23:44 (UTC), posted by SE-user Daniel Mahler
answered May 15, 2015 by (255 points)
I don't get how could a virtual image be prefocused

This post imported from StackExchange Physics at 2015-05-15 23:44 (UTC), posted by SE-user Azad

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