Spanish newbie (with a couple of CNC projects for photography)

[blackburn mark]

for focus stacking i would just concentrait on camera stability and hand crank a gearbox attached to a 1mm pitch screw to drive it (backlash wont be an issue as you will only be driving in one direction at a time)
if your using CS5 i dont think you need overly consistant steps as long as your steps dont over reach your depth of field... if your taking a pictures of insects the slide only needs to be short

selecting the right ratio gearbox will take a little bit of maths (you dont want to be cranking it 30 times between each frame)

let say your typical DOF is 0.1 mm then your probably safe to crank 0.05mm at a time.
ergo, 1mm pitch screw 20/1 gearbox would give you 0.05mm per revolution
if you were going to play it safe a 40/1 gearbox would give you 0.025mm and a bumble bee would need aprox 680 frames.... OWCH!!!! i hpoe you can get a wider DOF than 0.1mm :)

a single linear bearing and short piece of rail would be ideal, pre-loaded if you can, they do come up cheap on ebay now and again as most people will only buy them in sets of four