I found this article on hacking macro lenses. The author used a lens extension tube to allow closer focusing. IE The lens's Minimum Object Distance (MOD) was significantly reduced.
I cannot find an affordable lens that suits my requirements, so I would also like to extend or shorten an existing lens to achieve my goals. Basically I am trying to hack a close-focus machine vision industrial camera from an S-Mount Raspberry Pi camera. The problem I'm running into is that compatible lenses have too high MODs. Given the constraints below, how do I solve the variables?
- Object Size: 4" x 5"
- Object Distance: 4.5" (Object to Lens)
- Camera Sensor: 0.25"
- The Object should be in focus and snug to the edges of the captured image
- Avoid fish-eye or wide angle lenses, if possible
- Focal Length (Lens to principal focus)
- Image Distance / Back Focal Length (Lens to sensor)
I found this article which discusses Optics and the Lens Equation. I could simply solve the lens equation as follows: 1/115 mm + 1/x = 1/6 mm. In this case, the image distance would be 6.3303 mm. Is it really that simple though?
I can use any standard lens (3 mm, 4 mm, 6 mm, 8 mm, etc). My concern is that extension rings result in image magnificaion which would cut-off the image. I could plug my numbers into the magnification equation. and then extend my object size to include a 20% buffer, for example. But making that adjustment changes the figures for the lens equation. The two equations are intrinsically linked and I'm not sure how to solve them inclusively.