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Z7ii with 105 s macro lens focus shift question

Started 4 months ago | Questions thread
john isaacs Veteran Member • Posts: 8,414
Re: Z7ii with 105 s macro lens focus shift question
2

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).

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Panasonic GH5 Olympus E-M5 III Olympus E-M1 III Nikon Z6 II Nikon Z7 II +15 more
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