# How much does a step move the focusing ring?

Does anyone know about how much a lens step rotates the lens? I’m just after an approximation for field use. In other words you are out in the field and want to shoot a stack. My goal is to be able to focus the camera on the close part and then focus on the far part paying attention to how much I turned the focusing ring.

Where this comes from - with Magic Lantern to do focus stacking you need to set a number of steps and a step size. The step size is a number that moves the focusing ring a given amount. This number goes from 1 – 10. With a 50mm Canon macro lens, 50 steps move the ring around one inch. This is not exact at all - just a ball park amount. With the 50mm lens you can see how much it turns when the stacking is being done. If you do 20 steps with a step size of 1 it moves the focusing ring about a ¼ of an inch. With 20 steps at a size of 2 it moves around ¾ of an inch. With 10 steps and a step size of 10 it moved around 2 ¼ inches. None of this comes up with 50 steps per inch. But if you used 50 steps for the distance traveled you should have a good stack. Naturally the number of shots you took would have to be determined based on magnification and aperture.

This should work for a 50mm but the 100mm moves internally so you have nothing to compare it with. Any ideas on how to come up with something that would be somewhat useful?

• Why does it matter? What problem are you trying to solve? Feb 25, 2016 at 16:10
• It will depend so heavily on the lens that any single answer is likely to be useless. Feb 25, 2016 at 16:39
• It can also depend on the Implementation of the focusing motor, if it is by-wire. E. g. on my Fuji 35mm 1,4, a slow movement of the ring results in a small change of the focus point, a fast one over the same distance in a big change. Weird at first, but you can be very accurate once you get used to it. Feb 25, 2016 at 23:33
• magiclantern.fm/forum/index.php?topic=16659.msg162352#msg162352 may be of interest - looks like a thriving community of developers and scripters that may already have a workable solution available. Feb 26, 2016 at 13:34