I’d like to discuss and demonstrate various lens defects. These defects are called aberrations in particular. We, I have the diagrams here for a couple of different aberrations. I have SP collaboration and chromatic aberration. Let’s talk about spherical collaboration first. with fair collaboration.

We have light rays coming in close to the axis here. For example, Ray one, a and Ray one B as I’ve labeled them will cross the axis at the focal point for those two rays. Whereas rays further out might have a different focal point. And if they do then Ray two, a and Ray two B for example, could cross the actions at this point here, that’d be the focal point.

For those two rays. And when we have inner rays and outer raise with different focal points, then the focal point becomes ambiguous for raisin between one and two. We’d have a focal point somewhere between F1 and F two. So if we have an ambiguous focal point, then we have an ambiguous image, plane, and therefore we have a blurry image.

And then chromatic aberration is where you have. For example, white light come in two parallel beams of white light, parallel to the axis come in. And blue light has a shorter focal point than does red light. So because of dispersion the light. We’ll spread out into his component colors. And we have an ambiguous focal point because of the coloring that takes place.

We call that chromatic aberration. And of course, all of the other colors would be in between here. So we have a whole series of focal points for for the different colors. We call that chromatic aberration. And again, if you have a a lens. where you have chromatic aberration. You have an ambiguous focal point.

You’d have an ambiguous image, plane. And so the different colors of light would form try to form images at different positions and you’d end up with a blurry image due to coloring. Now I’d like to demonstrate both of these types of defects using the Blackboard optics for the Blackboard optics turn on the light source.

And I have a receiving screen here so we can follow the Ray of light as they, as they leave this source here as a parallel bundle of rays. And let’s watch what happens when the light passes through, for example, a converging lens and that light then will converge to a focal point. And let’s turn the lights down for better contrast.

And we’ll be able to demonstrate that.

So here we see that light from the outer part of the lens, for example goes down, crosses the the axis at a different place than light from the central part of the lens. And as I move this up and down, we can see the light from different places will cross the axis at different locations, depending upon the shape of the lens at that particular place where the light passes through.

And if the lens isn’t properly shaped, then we have what’s called spherical aberration. Grammatic. Aberration is starting to show up here as well, but it’s a little more difficult to see to do that. I’m going to take a And even more converging lens by putting two converging lenses together, getting a shorter focal point.

So we can emphasize that a little bit more here again, you see the spheric collaboration with the ambiguous focal point, but notice also that the light because of dispersion goes off in in different directions there slightly differently. Depending upon the color of the light, the blue light refracts, the most, the red light refracts a little bit less.

And so we have coloring take place here and we have a focal point. That’s slightly colored because of chromatic aberration. so we see the spherical collaboration where all the white light has an ambiguous focal point, but within that white light, there’s that other subtle aspect of chromatic aberration, where the different colors also have a slightly different focal point demonstrating spherical collaboration and chromatic aberration.

Now I can demonstrate that even more. So within the, with an extreme lens, let me turn the lights up so you can see this a little better. Here I have a lens where we’re gonna have some rather severe SP collaboration and possibly also some severe chromatic aberration. This lens has the approximate shape of a of a nice lens, but let’s see what happens when we turn the lights down and let the light shine through through this Semicircular piece of plastic and let’s follow the the rays of light for this to do this, I’m just going to take three rays of light here and let that light come up.

And we see that we have those, we have those three rays of light. That do not come to a common focal point. They come up parallel. They do not come to focal focal point because of spherical collaboration. And we also see a more pronounced chromatic aberration with within each of those beams.

The light goes off in colors as if there this were a corner of a prism. So we had both fair collaboration and chromatic aberration demonstrated with, with this semicircular piece of plastic.