What Lenses Are Needed for Minimal Movement and Infinity Focus?

[artiswar]

Posted a while back but to no avail. I've since done some tinkering but need a little bit of help perfecting the math.

I've constructed an experimental version of the above set up with success. Moving the plano-concave element away from the plano convex element brings the focal point towards the sensor. Moving the concave element back towards the convex element pushes the focal point further away.

What I'm trying to figure out is what power or focal length lenses I need to construct this. I want minimal movement (around 5-10mm) and to be able to achieve infinity (afocal). Any advice is much appreciated!

 

[M Quack]

Are you familiar with ray transfer matrix analysis?

http://en.wikipedia.org/wiki/Ray_transfer_matrix_analysis

You should be able to model your configuration with such matrices, leaving the geometrical parameters (radius of lens elements, distance between the plano-convex and plano-concave elements) as variables.

You then solve for the distance for focus to the nearest point and to infinity.

 

[artiswar]

I should have specified, I only hold a BA. I'll do some research on this.

 

[M Quack]

As long as you manage to multiply 2x2 matrices you'll be fine.

In the worst case you can write a little computer program in python or basic and tweak the parameters until you get what you want.

 

[sardar]

Hello,

Thank you for reaching out for help with your focusing lens block experiment. It sounds like you have made some progress with your setup, and now you are trying to determine the necessary power and focal length for your lenses.

To calculate these values, you will need to use the lens formula, which relates the focal length (f), object distance (u), and image distance (v) of a lens:

1/f = 1/u + 1/v

In your setup, the object (plano-convex lens) is located at a fixed distance from the sensor, and the image (focal point) can be moved by adjusting the distance between the two lenses. To achieve infinity focus, the image distance (v) should be equal to infinity, meaning the focal point will be at a distance of 5-10mm from the plano-convex lens.

To determine the necessary focal length for your lenses, you can rearrange the lens formula to solve for f:

f = uv/(u+v)

Where u is the distance between the object and the first lens (plano-convex) and v is the distance between the two lenses. By plugging in the values you want (u = 5-10mm and v = infinity), you can calculate the necessary focal length for your lenses.

Additionally, to minimize the movement of the lenses, you will want to use lenses with a larger focal length. This will result in a smaller change in the focal point for a given distance between the lenses.

I hope this helps you in perfecting your experiment. If you need further assistance with the math or have any other questions, please don't hesitate to ask. Best of luck with your research!