# Geometrical optics

1. Sep 18, 2015

### isnainidiah

How do you use Fermat's principle of least time to explain various concepts in geometrical optics?

2. Sep 18, 2015

### Staff: Mentor

You can use Fermat's principle to derive the laws on which geometrical optics is based: The laws of reflection and refraction.

3. Sep 18, 2015

### Staff: Mentor

For example, do a Google search for "law of refraction fermat principle" and you'll find many web pages and even a video which try to explain how the law of refraction can be derived from Fermat's principle. If you don't understand one of those derivations, post a link to it and ask questions about the specific things that you're stuck on.

4. Sep 18, 2015

### isnainidiah

Okay thank you,,

So when we talk about optic geometry, we just explain the reflection and refraction, isn't it ??

then what if the answer to the question "how do you use Fermat's principle to explain the need for forms of mirrors and lenses"?

5. Sep 18, 2015

### Staff: Mentor

Yes. That is the basis of geometrical optics.

I don't quite understand the question. Use Fermat to derive the laws of optics, then use those laws to design mirrors and lenses to do what you would like (form images, for example).

6. Sep 18, 2015

### isnainidiah

Yeah i mean, how we use fermat principle to explain the required shapes of lenses and mirrors ?

7. Sep 18, 2015

### blue_leaf77

Usually, the need for designing certain shapes of the mirrors and lenses is for aberration correction purpose. Aberration comes in various forms, all of them have adverse effect on the formed image, so suppressing them by designing certain shapes and/or material of the mirrors and lenses is demanded.

8. Sep 18, 2015

### isnainidiah

So, the design of mirror and lens just for certain purpose, is'n it?
Then, we derived the fermat principle that can we use to design the mirror and lens for certain purpose, is'n it

9. Sep 18, 2015

### Staff: Mentor

10. Sep 18, 2015

### blue_leaf77

The (practical) purpose for which lenses or mirrors with certain shapes needs to be produced usually comes first, then one applies the theories either through Fermat's principle or merely ray tracing to analyse the optical elements.

11. Sep 18, 2015

### isnainidiah

I asking about basic shapes of lenses or mirror and also another shapes of lenses or mirror,

12. Sep 18, 2015

### isnainidiah

So, we need the purpose first,
then we can use many theories to analyse it, isn't it ?

13. Sep 18, 2015

### blue_leaf77

It should be that way, you don't normally use your design software to design optics as a plaything as weird as you want (except for learning purpose). There must be a specific purpose for certain optics design.

14. Sep 18, 2015

### isnainidiah

Okay, thak your for the explanation