How much dof can you get with a large aperture on a PC lens?

Started 3 months ago | Discussions thread
BillW1204 Forum Member • Posts: 97
Re: Measure with a micrometer, cut with an axe.

Michael Benveniste wrote:

Mirvin wrote:

Measuring accuracy is really important, especially for wide angle lens if you want the closest focus you can get. In the above example focusing to 5.53 ft will get a focus depth from 2.77 ft to infinity. If you make a mistake and focus to 5 ft, then the focus depth is 2.63 ft to 51.23 ft.

Suppose I told you for a 20mm lens on a D850 at f/8, that the calculator I use states that the hyperfocus distance is 6.559 ft, and a reasonable case can be made for any value ranging from 4.687 to 18.885 ft or even a bit longer?

The problem is that there's one definition for something being "in focus." Instead, hyperfocal distances assume something called a "circle of confusion," which is the largest circle recorded on the sensor that the viewer will still perceive as a single point. Obviously, there's a lot of wiggle room in that definition, as different people have different visual acuity and view photographs in different ways.

The 5.53 foot value you cite assumes a Circle of Confusion of 0.030 mm. That's a holdover from the film era, although values of 0.025mm to 0.035mm were often frequently used. It assumed that the viewer with average adult vision was looking at an uncropped print from a distance equal to the longest dimension of the shot. So, for example, the assumption is that someone would be viewing an 8x12" print from a about 1 foot away.

Today few people judge whether something is "in focus" that way, I doubt any D850 owners are among them. Once you start judging on a monitor, traditional CoC measurements underestimate the necessary hyperfocus distance. And once you start looking at 100% crops from a D850, it underestimates it a lot.

Does that mean you shouldn't use 5.53 feet or whatever to compose your shot? No, but it also means that if trying to achieve that false precision means you don't get the shot you want, or that it sucks the fun out of shooting, you're better off just picking a spot "by eye" and using depth-of-field preview or live view to see if you're getting what you want.

Do you recommend a particular CoC for depth of field calculations?  Assume a high resolution camera like a D850 or Z7, with photos viewed on a high resolution screen like a 27” retina screen iMac or printed say 13x19.  The apps I use also factor diffraction into the calculation.  I have been using 0.015 mm on the assumption it was “safer” to use a higher standard than 0.030 mm.

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