How to determine the focal length of a random lens? Here's how: EO video.

[Alaskan]

I have found a very simple explanation of how to determine the focal length of an unknown lens, thought it would be worth a share.

 

[Alaskan]

This method works great, so simple. One thing I want to add is the distance from the lens and the collimated laser source (laser pointer) going into and through the lens does not matter, it's how far away the output of the lens is to the target when the dot is at its smallest possible size is the focal length.

Of course, if the laser you are using is not fully collimated, you will have error.

 

[steve001]

This method works great, so simple. One thing I want to add is the distance from the lens and the collimated laser source (laser pointer) going into and through the lens does not matter, it's how far away the output of the lens is to the target when the dot is at its smallest possible size is the focal length.

Of course, if the laser you are using is not fully collimated, you will have error.

Edmund Optics offers a lot of optical information than most other companies I think.