The other day I saw this link from dsvilko and thought it was a really good idea. He uses the sled from a cd or dvd player to accurately position a subject for macrophotography. If you have never tried it before, then shooting something macro usually means that there is very light coming in to the camera and it makes manually focusing something (by twisting the lens) almost impossible.
Initially I wanted to directly duplicate dsvilko’s rig, but the sled I have doesn’t have the belts traveling in the same direction as his, so there was no easy way for me to replace the dc motor with a stepping motor. I decided to just roll with the punches and stick with what I had. By limiting the amount of time the motor was on I could build a reasonable facsimile of a repeatable step. I am currently moving the sled in 20 millisecond periods.
I directly soldered wires to the existing motor’s terminals. I zip tied them to the sled and then started work on the arduino side of things. I am using a l298 h bridge motor driver to control the motor. It takes 3 wires from the arduino. Two wires control the direction of the motor, and the third turns it on.
I also added an ir receiver diode so that I could use a remote control. I have it set up so that an apple remote can step it in single steps or groups of 10 in either direction and you can set a “home” position and then return to that position with the push of a button. Everything runs off of usb power via my laptop (possibly not a good idea).
The main reason for building this as opposed to a sliding sled is that you can do what is called “focus stacking” with this. Macro photography will sometimes have an area of the subject that is in focus (focal plane) that is only a millimeter thick. Focus stacking enables you to have a wider focal plane by combining photos. There is software that cuts the in-focus sections of each photo and layers them all into one file. I have only done this once (just this morning!) but it seems really really cool. I used an app called Helicon Focus once I had enough photos and it did as promised. It combined 30 photos that all looked like this