I found this article on hacking macro lenses. The author used a lens extension tube to increase the magnification of a standard lens into a macro lens. To my surprise the lens's Minimum Object Distance (MOD) was also significantly reduced. The photos he took appear to be slightly distorted and have shallow depth of field. Will this happen with all lenses and extensions? Will resolving power be reduced?
Here's how I would like to apply this concept. I am trying to hack a close-focus machine vision industrial camera using cheap parts. The camera needs to focus on a 4" x 5" region with a working distance of 4"-5" inches between subject and lens. I used an online calculator to determine that I need a 5-6mm focal length camera lens to maximize the subject in the photos. The problem I'm running into is that most lenses have a MOD greater than 8". So I would like to instead use a 3mm lens with a 2.5mm extension. Could this work?