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What Does Depth of Field Mean on a 36 Megapixel Camera?

B&H Photo has the Nikon D4, Nikon D800 and D800E and Canon 1DX available for pre-order. See the gear pages for Nikon and gear pages for Canon.

At close range at f/8, depth of field is very shallow. Read more below.

(Larger image can be viewed in Making Sharp Images)

Poppy on Blue
Nikon D3 + Coastal Optics 60mm f/4 UV-VIS-IR APO macro @ f/8

Geophysicist Glenn K writes to say:

Per pixel (sample) noise levels have to be significantly higher to outweigh the benefits of higher sampling frequencies... and as recent DX/APSC cameras have shown, noise levels are under pretty good control at remarkably small pixel pitches these days. The value of higher sampling frequency is even more important given the Bayer matrix approach to color, since color interpolation distances decrease.

You might also remind people that thinking about the image cast by the lens being sampled by the sensor is also valuable when considering depth of field. At a given image size and viewing distance, finer pixel pitch really doesn't change depth of field, its just that film and coarser sensors simply blurred things out more... and if the image needs the DOF, use it... it's the image that matters, not the per pixel sharpness in the end.

I am really curious if there is much difference between the 800E and 800. After all, the AA filter should need to be very mild with that pixel density and it could be that lens sharpness and diffraction make things a wash... I certainly don't see much difference between the two samples that Nikon has posted... and give questionable technique, who knows what the real difference is... could just be a way to grab 10% more per body to offset the strong Yen :-)

DIGLLOYD: As Glenn correctly points out, depth of field is purely an optical property which is fixed by optical laws, and thus bears no relation which sensor or film is recording the image; the particular sensor or film is merely a sampling frequency of whatever happens to be projected by the lens.

However, depth of field has always been discussed in a context of “how big a print”, which fixes the “acceptable” amount of blur. Since the photosites (pixels) are much smaller on a 36MP camera than on an 16-18MP camera, the amount of acceptable blur is lower, at least if one wants more resolution., since blur beyond the size of a photosite is thus smeared over more than one photosite. The Circle of Confusion (a blur dot) and diffraction (a more complex blur dot) get involved in that computation.

I generally simplify this to an actionable “how many real megapixels of detail can I capture”— which means a balance between stopping down (more depth of field) and diffraction ( loss of contrast and then loss of detail). Both subjects are explored in detail in Making Sharp Images. On the 36MP Nikon D800 / D800E, aperture f/5.6 is the point at which that balance tilts; stop down beyond that point and contrast is rapidly lost on fine detail, then resolution starts to be lost as well. However, f/8 should hold up well enough that its extra depth of field is worth it over f/5.6. The lens also has an influence; a lens that is world class will provide acceptable contrast a bit longer on the finest details. A mediocre lens might not provide good contrast even at its best; the image is optically limited to begin with.

Looking at it another way, at f/8 on the 36-megapixel D800/D800E, there is exactly the same depth of field (by whatever definition is used). But outside a very shallow zone which resolves to the sensor capabilities, the blur quickly becomes larger than the photosite size, and thus the increased sensor resolution is in fact only more detailed sampling, carrying no more detail than a camera with lower resolution. Still, that increased sampling density has its benefits when downsampled to the resolution of camera with (for example) half the resolution— all sensor qualities being otherwise equal of course. And in an intermediate zone, it might still have oversampling benefits to reduce aliasing as well.

A fast (bright) aperture = shallow depth of field

More depth of field is not better or worse. It depends on the goal of the photograph, and the subject matter. Sometimes less is more, much more! Which is why an f/3.5 - 5.6 zoom is a paperweight for my purposes— lousy quality to begin with, and no versatility.

Regardless of sensor resolution, there is no substitute for a fast (bright) aperture to separate subject from background. One that combines a high level of color correction and very good contrast, such as the Leica 50mm f/0.95 Noctilux-M ASPH for the Leica M9.

Although one can argue that Canon’s 85mm f/1.2L II has even more background blur, the fact is that f/0.95 has a look all its own, at least the look that the Noctilux produces. Still, I highly recommend all f/1.2 lenses as superb creative tools.

Bristlecone stump, sampled for science
Leica M9 + Leica 50mm f/095 @ f/0.95
Snow Cat high in the White Mountains
Leica M9 + Leica 50mm f/095 @ f/0.95
Having fun high in the White Mountains
Leica M9 + Leica 50mm f/095 @ f/0.95

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