I have the following items:
- a round target object, approx. 6mm in diameter
- a lens, focal length 20mm, F/2.8
- a camera sensor, optical size 1/4" (note: I know this camera has a fixed-at-infinity lens, but I can pop it off so it has no lens at all)
I need to take a picture of the target object, through the lens, using the camera sensor. I'm trying to figure out how to position these items (distances between them) such that the object is in focus and fills the camera sensor.
This online calculator suggests that for a lens with the above specifications, and a target area of 6mm x 8mm, the object should be 4.44cm from the front of the lens. How, though, do I calculate the distance from the back of the lens to the camera sensor? I know I could use the focal length for a focus at infinity, but that would require the object to be at least 5m or so beyond the lens, which is far outside of the allowable distance for this application.