The DOF Calculator featured in Zerene Stacker is by far the best tool for determining depth of field and the safe step size for focus bracketing. Rik Littlefield, creator of Zerene Stacker, recently released an online interactive version of DoF Calculator. Sincere thanks to Rik for sharing his expertise!
How to use the calculator
There are several ways to use the DOF Calculator, as shown in the following screen capture. I used two methods to calculate the “safe step size” (with 20% overlap) for focus bracketing with all of my basic macro photography rigs.
Choose Option 1 for the best quality focus stacked composite images. Set the aperture for your camera lens to its “sweet spot.”
Choose Option 4 if you are using a microscope objective for a macro lens.
As you can see in following examples, it isn’t necessary to input values for every field in the calculator.
AmScope / Reakway 4x microscope objective
Determining depth of field – safe step size for a 4x microscope objective is the simplest calculation of all my macro photography rigs. All you need to input is the “NA” (numerical aperture) that’s labeled on the side of the microscope objective. In this case, the NA equals 0.10.
It’s recommended that you use a 20% overlap between steps. Input a value of 0.2 in the field for “Step overlap.”
DoF: 0.054862 mm (54.862 microns)
Step size (suggested) at 20% overlap: 0.04389 mm (43.89 microns)
Let’s apply the output from the DOF Calculator (shown above) to my relatively new NiSi Macro [manual] Focusing Rail NM-200. The larger adjustment knob is shown below. One full rotation of the knob moves the carriage one millimeter, or 1,000 micrometers (microns). The knob is marked in 100 increments, so each increment on the knob is 10 microns. Every numbered increment is 100 microns.
For my 4x microscope objective, I would turn the adjustment knob four (4) increments between shots or 40 microns (rounded down from 43.89 microns). It’s OK to use a smaller step size than the DOF Calculator recommends.
Laowa 25mm Ultra Macro (at 2.5x, f/4) plus Fujifilm X-T3
The Laowa 25mm Ultra Macro lens can be set for magnifications ranging from 2.5x to 5x. The following example shows the lens set for 2.5x. Input a magnification of 2.5, and a lens F-number of 4 (an aperture of f/4 is the “sweet spot” for this lens).
DoF: 0.068854 mm (68.854 microns)
Step size (suggested) at 20% overlap: 0.055083 mm (58.038 microns)
For the Laowa 25mm Ultra Macro lens, I would turn the adjustment knob on my NiSi NM-200 five increments between shots or 50 microns (rounded down from 58.038 microns).
Fujinon 80mm macro (1x, f/8) plus Fujifilm X-T3
The Fujinon 80mm macro lens is one of the sharper lenses I own. Maximum magnification is 1:1 (life size).
DoF: 0.56306 mm (~563 microns) ← remember 1 mm = 1,000 microns
Step size (suggested) at 20% overlap: 0.45045 mm (~45 microns)
Each increment on the NiSi NM-200 manual focus rail is equal to 10 microns. For my Fujinon 80mm macro lens, I would turn the adjustment knob four numbered increments between shots — equal to a distance of 40 microns (rounded down from ~45 microns).
Canon 100mm macro (1x, f/11) plus Canon EOS 5D Mark II
The Canon 100mm macro is another one of the sharper lenses I own. Maximum magnification is 1:1 (life size).
DoF: 1.0647 mm (1064.7 microns) ← remember 1 mm = 1,000 microns
Step size (suggested) at 20% overlap: 0.85176 mm (851.76 microns)
Each numbered increment on the NiSi NM-200 manual focus rail is equal to 100 microns. For my Canon 100mm macro lens, I would turn the adjustment knob eight numbered increments between shots — equal to a distance of 800 microns (rounded down from 851.76 microns).
Canon MP-E 65mm macro lens (1-5x) plus Canon 5D Mark II
The Canon MP-E 65mm macro lens can be set for magnifications ranging from 1x to 5x. The following example shows the lens set for 3x.
DoF: 0.12251 mm (122.51 microns)
Step size (suggested) at 20% overlap: 0.098008 mm (~98 microns)
Remember, each increment on the NiSi NM-200 manual focus rail is equal to 10 microns. For my Canon MP-E 65mm macro lens set for 3x magnification, I would turn the adjustment knob nine increments between shots — equal to a distance of 90 microns (rounded down from ~98 microns).
Related Resource
What if you don’t know the magnification of the macro rig you’re using? Or maybe you add an extension tube and/or close-up filter to a 1x macro lens — how does that change the magnification of the lens?
How to measure magnification provides photo-illustrated step-by-step directions, including sample math calculations.
The Backstory
I have been working behind the scenes trying to figure out how to determine focus bracketing step size for a variety of macro photography gear that I own. I have tested many depth of field – step size calculators and all of them are fatally flawed in one or more ways except for the one in Zerene Stacker.
See How to calculate step size for a long thread of posts related to my search for the answer to what turned out to a more complex process than I imagined. Thanks to the many members of photomacrography.net, especially Rik Littlefield, who kindly and patiently answered all of my questions.
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