Re: Z7ii with 105 s macro lens focus shift question
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Billstek wrote:
What would be a good setting for focus stacking individual flowers— f stop, how many frames, what width? I’m finding that I run out of depth before I get to the back of the subject, leaving the back out of focus. I can do it manually, but would prefer the automatic option.
None of this is well documented, but I use the following rule of thumb for close up photography (not for macro photography).
I assume that a step width of 1 is about 1/8 the standard depth of field calculated from the standard circle of confusion (CoC) of 0.03. So all you need is a DOF calculator and you can calculate how many step sizes you need to get a certain depth.
If your flower is 3" tall and deep, then the image will be 4" tall at 1.5 feet and you will want a depth of 3" to capture it. This is for a 105mm lens, and is proportional so if you want an image that is 8" tall, the distance would be 3 feet.
Use a DOF calculator to calculate depth of field. This is dependent on focal length (105mm) and aperture. An aperture of f/8 will provide sharp images with significant DOF. You can go with smaller f/number (f/5.6), but then you need more images. You can go with larger f/number (f/11), but then you get less sharp images with diffraction.
The DOF with 105mm lens, f/8, at 1.5 feet is 0.3".
The number of steps needed is
StepNumber = Depth / DOF / StepWidth * 8
Or 3" / 0.3" / 1 * 8 = 80 steps.
But do you need a step size of 1? I tend to use a step size of 3 for standard full frame like the Z6ii, and a step size of 2 for high resolution sensors like the Z7ii. For crop sensors I adjust the CoC by the crop factor.
There is a useful online calculator here:
https://www.pointsinfocus.com/tools/focus-stack-calculator/#comments
In the field, it is easy to adjust these calculations to compensate for changes. All you need to remember that the DOF at f/8 and 1.5 feet is 0.3". If you change aperture, the DOF changes linearly with f/number (at f/16, it is 0.6"). If you change distance, the DOF changes with the square of the proportional change in distance (at 3 feet, it is 4 times as large, or 1.2").
So, for a 3" flower, I would focus at 1.5 feet and use a step width of 2 and 50 steps (fudge the 40 steps I calculate just to be conservative).