# Spherical Aberration Explained - Chris' Experiments

• cavis
In summary, the conversation is about spherical aberration in experiments with a concave mirror. The image on a flat piece of paper appears blurry due to the aberration, but when looking directly into the mirror, the image appears sharp. This is because the eye acts as a small aperture, reducing the effects of aberration. The suggestion is made to try using a circular aperture to improve the projected image.
cavis
Hi there,
I'm having a little confusion regarding spherical aberration from some experiments I've been doing with a concave mirror. I've been directing the mirror so that it faces the distance (ie. objects at infinity) and then positioning a flat piece of paper so that an image forms on it. The image, even at is sharpest, remains somewhat blurry which is due to spherical aberration from the mirror, as far as I understand.

And yet, when I look at the distance directly in the mirror (without looking at the screen), I see an image that is perfectly crisp. What am I missing here?

Chris.

What's the focal length, diameter, and F-Ratio of your mirror?

How far from the mirror are you placing your eye when you look in it? Very close to the focal plane, behind it, or in front of it?

It seems to me that your eye may only be getting part of the converging light cone from the mirror. If you take only a small piece of the light cone, the spherical aberration is greatly reduced.

cavis said:
Hi there,
I'm having a little confusion regarding spherical aberration from some experiments I've been doing with a concave mirror. I've been directing the mirror so that it faces the distance (ie. objects at infinity) and then positioning a flat piece of paper so that an image forms on it. The image, even at is sharpest, remains somewhat blurry which is due to spherical aberration from the mirror, as far as I understand.

And yet, when I look at the distance directly in the mirror (without looking at the screen), I see an image that is perfectly crisp. What am I missing here?

Chris.
That's a very astute observation. I agree with Drakkith about the reason. When you look at the image directly, you are effectively putting a tiny aperture in the way (your pupil), which means that each part of the image you are looking at is coming from only a small part of the reflector and the errors are small.
In cameras, the lens distortions are always less and the depth of focus is always much greater when using a small aperture. You could try putting a circular aperture in the way of your mirror and see how the projected image improves.

## 1. What is spherical aberration?

Spherical aberration is an optical phenomenon that occurs when light rays passing through a spherical lens do not converge at a single point, resulting in a blurred or distorted image.

## 2. How does spherical aberration affect image quality?

Spherical aberration can cause images to appear fuzzy, hazy, or distorted, reducing the overall sharpness and clarity of the image. It can also cause a decrease in contrast and color accuracy.

## 3. What causes spherical aberration?

Spherical aberration is caused by the spherical shape of a lens, which causes light rays passing through the edges of the lens to be refracted differently than those passing through the center. As a result, they do not converge at the same point, leading to a blurred image.

## 4. Can spherical aberration be corrected?

Yes, spherical aberration can be corrected through the use of specialized lenses, such as aspheric lenses, which have a non-spherical shape that helps to reduce the effect of spherical aberration. Additionally, using multiple lenses in a compound lens system can also help to correct for spherical aberration.

## 5. How can I prevent spherical aberration in my experiments?

To prevent spherical aberration, it is important to use high-quality, precision-crafted lenses with minimal spherical distortion. Additionally, carefully controlling the position and alignment of the lenses can also help to reduce the effects of spherical aberration.

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