Second Focus

So let's solve for the focal length.

Or they can be, I don't want to say always.

So f squared minus a square.

And what we want to do is, we want to find out the coordinates of the focal points.

Let's get back stereo rig.

Select the second focus of the new ellipse...

Now we're asking you what is the focal length if an object of size 20 m that is 400 meters out if we observe it to be 1 mm on our projection surface.

Select the second focus of the new hyperbola...

In the last video, I told you that if I had a hyperbola with the equation x squared over a squared minus y squared over b squared is equal to 1, that the focal distance for this hyperbola is just equal to the square root of the sum of these two numbers.

And then I have this distance over here, so I'm taking any point on that ellipse, or this particular point, and I'm measuring the distance to each of these two foci.

Now in the hyperbola, what is the difference of the distances to the two foci?

Focal length

Focal

Focal Length

Focal blur

Focal point

First Focus

Focal Length

Focal length

And this is f2.

And it's for focus.

Focal length of the lens

Well, we just used the distance formula.

So there's one point that just by looking at it we could say is going to be in our locus.

There and there.

We have focused on the worst case scenario.

That's our directrix and it has the equation y is equal to k.

Let's look at this in more detail.

Ellipse by Focuses Point

And we learned that the focus, the focal distance or the distance from the central of the ellipse, which is this distance right here that focal distance is just the square root of the difference of these two numbers.

The intersection of two objects

35mm equivalent focal length

That's this distance right there.

And that's what we set out to figure out in the beginning.

And you enter that space, and you feel like, Wow!

Requires great focus.

Just focus.

Bifocals.

Your focus,

It looks something like that.

Hyperbola by Focuses Point

I just factor out the x squared there, minus y squared is equal to f squared, the focal length squared, minus a squared.

But the whole point of this video is to discuss foci, and you might have guessed and I did touch on it in the last video that hyperbola also have foci, but they open.

The focal length, f squared, is equal to a squared minus b squared.