DOF calculations and circle of confusion

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Hartyewh New Member • Posts: 15
DOF calculations and circle of confusion
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Hi,

I just got a 5D4 and a Sigma 85m f/1.4 Art and this is my first contact with a lens with a wider aperture then f4 so I've started to develop my intuition to control the depth of field in my photos. I started by checking some online DOF calculators, but ran into the circle of confusion which led me for hours down some serious rabbit holes on this forum as well.

I'm now making a DOF chart of distances and apertures and maybe something more for practice and my wife want's to do some nice visualization from it so I'd like the numbers to make at least some sense.

Could someone more knowledgeable comment on the values I've chosen so that they seem approximately valid? It would be very much appreciated!

I'm using this calculator since it allows to select the CoC: https://dofsimulator.net/en/

I chose a CoC of 0,017mm instead of the more classic 0,03mm to match my most commonly used viewing method a 65" 4K TV from 2 meters. One CoC calculation gave me 0,0176mm and the 0,017mm is the closest the calculator will give me. Also the size of the sensor's pixels is 0,00535mm which times two is 0,017mm and I understand this is a good thing.

Is this a reasonable CoC for reference purposes?

The chart will consist of the required distance from the subject (2m tall in this example) to fit vertically into the photo and a list of DOF's with common apertures like this. Example values from the calculator mentioned above:

DOF chart example

Any thoughts? I'm thinking of making some other charts as well about hyperfocal distance, different sized subjects (2m = standing person, 25cm=face etc) and see how the numbers behave if I can see some useful information that I could transform into an intuitive visualization.

Another issue I have is with the calculated distance to subject. For a 2m tall subject with a 24mm focal length every calculator gives a distance of 2m as well, but when I try it at home I'm at about 1,5m from the subject to fill the frame vertically with the 5D4 and a Canon 24-105mm f/4L II. I assume that the lens isn't actually a 19-105mm so where's the mistake?

Thanks a lot for any comments or ideas!

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