Potential dead horse: how bad is FF's deep DoF disadvantage?

Started 4 months ago | Discussions thread
Mike Davis
Contributing MemberPosts: 686
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Re: Zero
In reply to Lee Jay, 4 months ago

Lee Jay wrote:

sportyaccordy wrote:

So my question is, for folks who have used an array of different formats extensively, how much does this affect real world shooting?

Not at all. As you pointed out, for constant (deep) depth of field, all formats are the same.

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Lee Jay

True, except that smaller formats operate at faster shutter speeds to yield the same DoF and diffraction at any given enlargement factor and desired print resolution, and confining the small-sensor photographer to use of smaller f-Numbers and, potentially, fewer diffraction-free f-Numbers from which to choose among those that are available on the lens.

Example:

12 MP Panasonic Lumix DMC-TS1

Sensor Size: 6.13 x 4.16 mm

Largest possible non-resampled 360 ppi (5lp/mm) print: 8.27 x 11.02 inches

Enlargement Factor: 45.67x

F-Number at which diffraction would begin to inhibit a desired print resolution of 5 lp/mm in the final print: f/3.2

Maximum aperture: f/3.3 - f/5.9 (variable across zoom range)

Conclusion: Other factors ignored, thanks to diffraction alone, this tiny 12MP sensor can only deliver 5 lp/mm worth of true subject detail in an 8.27 x 11.02-inch print when shot wide open at f/3.2, using its shortest focal length. The diffraction-savvy photographer therefore has a choice of exactly one FL and one f-Number if a print resolution of 5 lp/mm is desired, but at f/3.2, the DoF and diffraction will be identical to that had at f/17.7 with the larger sensor - at a proportionately faster shutter speed.

vs.

12 MP Nikon D3 or D700

Sensor Size: 36.0 x 23.9 mm (more than five times larger than the Lumix DMC-TS1 sensor)

Largest possible non-resampled 360 ppi (5lp/mm) print: 8.27 x 11.02 inches (same pixel count)

Enlargement Factor: 8.34x (less than 1/5th the Lumix DMC-TS1 enlargement factor)

F-Number at which diffraction would begin to inhibit a desired print resolution of 5 lp/mm in the final print: f/17.7 (more than five times larger than the f-Number at which diffraction would begin to inhibit a desired print resolution of 5 lp/mm with the Lumix DMC-TS1).

Conclusion: Other factors ignored, thanks to diffraction alone, this larger 12MP fullframe sensor can deliver 5 lp/mm worth of true subject detail in an 8.27 x 11.02-inch print when shot at any f-Number less than or equal to f/17.7. If this 12MP fullframe sensor is equipped with an interchangeable lens offering stops from f/3.2 to f/22, the diffraction-savvy photographer has a choice of six stops that would not inhibit a desired resolution of 5 lp/mm due to diffraction: f/3.2 through f/17.7. At f/17.7, the DoF and diffraction would be identical to that had at f/3.2 with the smaller er sensor - at a proportionately slower shutter speed.

Note that f-Numbers smaller than f/17.7 could only be used with the fullframe sensor when the intrinsic depth of the subject space does not require as much DoF, but with the smaller sensor, you have no choice but to shoot wide open at the shortest focal length, all the time - to prevent diffraction from inhibiting a desired resolution of 5 l/mm in a non-resampled 360 ppi print of the same dimensions.

Thus aside from signal-to-noise issues, the difference caused by diffraction, between large sensor and small sensor, all else being the same, is one of available f-Numbers from which to choose and the shutter speeds at which identical DoF and diffraction can be recorded.

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