Ellipse by Focuses Point

Focal length

Focal

Focal Length

Focal blur

Focal point

First Focus

Second Focus

Focal Length

Focal length

And this is f2.

And it's for focus.

Hyperbola by Focuses Point

We have focused on the worst case scenario.

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

We focus on Parker. And move it.

Focal length of the lens

Well, we just used the distance formula.

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

Just focus.

Bifocals.

Your focus,

There and there.

Conic by Directrix, Focus Point

Well, the first thing you do is though I've never well, we could just figure out the focal length just by plugging into the formula.

Focal Length

Telescope focal length

Eyepiece focal length

So let's call that a directrix.

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

But the point is we are right on target.

So what's the reality?

This one's fun.

Set here equivalent focal length assuming a 35mm film camera, in mm. A value of 0 means the focal length is unknown.

The coordinate of this focus right there is going to be 1 plus the square root of 5, minus 2.

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.

Parabola by Directrix Focus

Just remember, you're going 1 over 4A below the vertex.

This is f1, this is f2.

An ellipse constructed by its focuses and a point that pertains to it

I won't revise this equation, but this is the fundamental equation that governs when things are in focus, for a lens.