# The relationship between object and image in mathematics

### Object image and focal distance relationship (proof of formula) (video) | Khan Academy Ray diagrams provide useful information about object-image relationships, yet fail to provide the information in a quantitative form. While a ray diagram may help. Get this answer with Chegg Study. View this answer. Already a member? Sign in · Previous questionNext question. Need an extra hand? Browse hundreds of. object size in image = Object size * focal length / object distance from The relationship between object size and distance is an inverse linear.

Use the widget as a practice tool. A constant challenge of photographers is to produce an image in which as much of the subject is focused as possible. Digital cameras use lenses to focus an image on the sensing plate, the same distance from the lens.

Yet we have learned in this lesson that the image distance varies with object distance. So how can a photographer focus objects within the field of view if they are varying distances from the camera?

Additional mathemtics chapter 1-FUNction (find the image of (object))

This is a constant challenge for photographers whether amateur enthusiasts or professional who wish to controle how much of the subject is focused. Depth of field is the photographer's term to describe the distance from the nearest to the farthest object in the field of view that are acceptably focused within the photograph.

The Photography and Depth of Field widget allows you to explore the variables affecting the depth of field. The f-stop or f-number of a camera lens is related to the size of the circular opening or aperture through which light passes on its way to the digital sensor. The greater the f-number, the smaller the opening and the less light that gets through to the sensor.

The circle of confusion is related to the limitation of the eye to resolve the detail of an image within a small region. And let me just be clear, this is this triangle right over here. I just flipped it over. And so if we want to make sure we're keeping track of the same sides, if this length right here is d sub 0, or d naught sometimes we could call it, or d0, whatever you want to call it, then this length up here is also going to be d0. And the reason why I want to do that is because now we can do something interesting. We can relate this triangle up here to this triangle down here.

And actually, we can see that they're going to be similar.

## The unreasonable relationship between mathematics and physics

And then we can get some ratios of sides. And then what we're going to do is try to show that this triangle over here is similar to this triangle over here, get a couple of more ratios.

And then we might be able to relate all of these things. So the first thing we have to prove to ourselves is that those triangles really are similar. So the first thing to realize, this angle right here is definitely the same thing as that angle right over there. They're sometimes called opposite angles or vertical angles. They're on the opposite side of lines that are intersecting.

So they're going to be equal. Now, the next thing-- and this comes out of the fact that both of these lines-- this line is parallel to that line right over there. And I guess you could call it alternate interior angles, if you look at the angles game, or the parallel lines or the transversal of parallel lines from geometry. We know that this angle, since they're alternate interior angles, this angle is going to be the same value as this angle.

You could view this line right here as a transversal of two parallel lines. These are alternate interior angles, so they will be the same. Now, we can make that exact same argument for this angle and this angle.

### Object image height and distance relationship (video) | Khan Academy

And so what we see is this triangle up here has the same three angles as this triangle down here. So these two triangles are similar. These are both-- Is really more of a review of geometry than optics. These are similar triangles. Similar-- I don't have to write triangles. And because they're similar, the ratios of corresponding sides are going to be the same. So d0 corresponds to this. They're both opposite this pink angle. They're both opposite that pink angle.

So the ratio of d0 to d let me write this over here. So the ratio of d0. Let me write this a little bit neater.

## Image (mathematics)

The ratio of d0 to d1. So this is the ratio of corresponding sides-- is going to be the same thing. And let me make some labels here. That's going to be the same thing as the ratio of this side right over here. This side right over here, I'll call that A. It's opposite this magenta angle right over here. That's going to be the same thing as the ratio of that side to this side over here, to side B. And once again, we can keep track of it because side B is opposite the magenta angle on this bottom triangle.

So that's how we know that this side, it's corresponding side in the other similar triangle is that one.

### Image (mathematics) - Wikipedia

They're both opposite the magenta angles. We've been able to relate these two things to these kind of two arbitrarily lengths. But we need to somehow connect those to the focal length. And to connect them to a focal length, what we might want to do is relate A and B. A sits on the same triangle as the focal length right over here. So let's look at this triangle right over here.

• The Mathematics of Lenses
• Object image height and distance relationship
• Object image and focal distance relationship (proof of formula)

Let me put in a better color. So let's look at this triangle right over here that I'm highlighting in green. This triangle in green. And let's look at that in comparison to this triangle that I'm also highlighting.

This triangle that I'm also highlighting in green. Now, the first thing I want to show you is that these are also similar triangles.

This angle right over here and this angle are going to be the same. They are opposite angles of intersecting lines. And then, we can make a similar argument-- alternate interior angles. Well, there's a couple arguments we could make. Or we know from the last video the distance of the object to the distance of the image is the same thing as A to B.

So this is going to be the same thing as this. So the ratio of the distances is also the same thing as the ratio of their heights. So let me write it this way. So the ratio of the distance from the object to the lens, to the distance from the image to the lens, is the same as the ratio of the height of the object to the height of an image, or to the image of that object.

So I just wanted to do that little low-hanging fruit there, since we set up all of the mechanics already. Anyway, hopefully you found that useful.