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    Focus Bracketing advice

    I've been using the Focus Bracketing feature on my 90D, which gives me choices in terms of the number of shots and the Focus Increment. These will vary with lens, aperture, size of and distance from the subject, but I was wondering if anyone had come across a formula for working this out in advance of pressing the shutter. At present I do it entirely by guesswork.
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    #2
    If you have one there are smartphone apps that will calculate DoF for you once you’ve entered all the required parameters, divide the DoF into the total depth you need to cover and you should get an indication of how many steps you need; you’ll need to add in a small percentage for contingency. I’ve never tried this as my cameras do not have this facility but I would think it should work. I do my focus stacking manually and refocus using the magnifier for each step.

    Ian
    Ian

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      #3
      Originally posted by Farider View Post
      If you have one there are smartphone apps that will calculate DoF for you once you’ve entered all the required parameters, divide the DoF into the total depth you need to cover and you should get an indication of how many steps you need; you’ll need to add in a small percentage for contingency. I’ve never tried this as my cameras do not have this facility but I would think it should work. I do my focus stacking manually and refocus using the magnifier for each step.

      Ian
      I already have DoF calculators on a couple of apps and I think that is certainly part of the answer. But as well as the number of shots, I need to select the Focus Increment which ranges from 1-10 with no indication of what that scale represents. It would be possible to experiment with different lenses at different apertures and at different distances, but the results of that would only be of practical use if they were to form a formula that could be added to the smartphone app..
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        #4
        I thought I'd try a little experiment so I took some photos of a steel rule so I could measure the change in distance of each shot with different increments. The table below shows some of the results. The 2nd and 3rd columns are showing the change in 32nds of an inch, so a bit less than a mm. But what this does show is that Canon's Focus Increments are on an ordinal scale, not an interval scale, the higher up you go, the greater the difference. If I did enough measurements I would end up with a graph that showed a curve getting increasingly steeper.
        Focus Increment f/2.8 f 8.0
        1 1 3
        4 2 5
        10 10 21
        EOS 90D with EF-S 35mm. Initial point of focus approximately 5 inches from the front of the lens.
        Last edited by BobSapey; 10-11-2020, 11:40.
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          #5
          That’s an interesting experiment Bob, clearly canon ought to provide a deal more information. Looks like your only option at the moment is to practice with the lense you intend to use to understand how the control works in that instance.

          Ian
          Ian

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            #6
            I thought I'd try the DPP 'Depth Compositing' tool to see how it compared with stacking in Photoshop. The resulting pictures appear identical to me, but DPP is a lot simpler for this task and faster because its all in one process.
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