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?

  • 1
    \$\begingroup\$ Why does it matter? What problem are you trying to solve? \$\endgroup\$
    – Michael C
    Feb 25, 2016 at 16:10
  • 1
    \$\begingroup\$ It will depend so heavily on the lens that any single answer is likely to be useless. \$\endgroup\$
    – Chris H
    Feb 25, 2016 at 16:39
  • \$\begingroup\$ 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. \$\endgroup\$
    – Vertigo
    Feb 25, 2016 at 23:33
  • \$\begingroup\$ 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. \$\endgroup\$
    – db9dreamer
    Feb 26, 2016 at 13:34

1 Answer 1


A lot depends on the focus distance. The same amount of focusing ring movement at a very close focusing distance will move the point of focus a LOT less than the same amount of focus ring movement at a far focusing distance. And when you move from one lens to another all bets are off, especially if you are measuring the movement of the zoom ring in inches rather than degrees of rotation. A larger barrel diameter will mean the same rotational movement will be larger in term of inches. But that's not really significant either because some lenses have longer focusing ring throws (the amount of rotation needed to go from minimum to maximum focus distance) than other lenses.


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