EE needs help with optics

[jtknep]

TL;DR Summary

Fixed lens limitation

I think this is a simple request but I’ve never been very good at optics and need help. I have a ccd video camera with a fixed lens. Images are in focus from about 20 cm to infinity. It has an angular fov of 60 degrees. Can someone explain how to add external lens(es) to magnify a plane image 4 times and focus at a distance of 3.5 meters? The magnified image can be inverted if necessary. Thanks!

 

[DaveE]

Since your desired image distance seems to be well within an acceptable range for the current camera design, you will want to look a telescope designs with a magnification of 4x. This may be as simple as two lenses with focal lengths f₁ and f₂. They are spaced apart by f₁ + f₂ and have a magnification of M=f₁/f₂=4. Of course it can get more complex, depending on what you care about. The web has tons of information about telescope design, find the stuff that makes sense to you and addresses your problem.
https://www.rocketmime.com/astronomy/Telescope/telescope_eqn.html

 

[jtknep]

Are you saying that I should simply put a telescope in front of the existing fixed lens? If so, what is the proper distance from the fixed lens to the first telescope lens? Thanks for your patience with my meager knowledge of this subject.

 

[DaveE]

Are you saying that I should simply put a telescope in front of the existing fixed lens? If so, what is the proper distance from the fixed lens to the first telescope lens? Thanks for your patience with my meager knowledge of this subject.

The short (approximate) answer is that depends on the FOV angle and the diameter of the telescope. You want to capture (or supply) all of the rays that the camera can see. But, as close as practical, to make the telescope design smaller and cheaper.

 

[renormalize]

Can someone explain how to add external lens(es) to magnify a plane image 4 times and focus at a distance of 3.5 meters?

Perhaps you can find a teleconverter lens that's compatible with your existing CCD camera lens: https://en.wikipedia.org/wiki/Teleconverter.