Tag Archives: blur

Commentary, Equipment, Photographic Myths and Platitudes, Technique

Photographic Myths And Platitudes — Diffraction Limited Aperture

October 20, 2017 G Dan Mitchell Leave a comment

It has been a while since I posted an article in my “Photographic Myths And Platitudes” series — so here is a new one! It is a bit different than some of the previous posts in that it is based on something I wrote elsewhere in response to a lengthy (and long-winded!) discussion that suggested hyper-awareness of the so-called diffraction-limited aperture.

What is the diffraction-limited aperture, you ask? It is a real thing — not a myth — though it is sometimes over-emphasized by overzealous techno-photographers. In simple terms, as you stop down a lens its potential maximum resolution declines as a result of diffraction blur. (Keep in mind that other factors affect sharpness, too. Also, this happens to every lens, from the cheapest to the most expensive — it is a universal optical phenomenon.) At some aperture, the increase in blur becomes significant enough, in a technical sense, to be more of a “limitation” on image sharpness than the ability of the sensor to record detail — e.g. the “number of megapixels” of the sensor. A simplistic interpretation of the concept suggests that a photographer should avoid other apertures in order to “get the sharpest image.”

As with many things in photography, it isn’t that clear-cut.

Now on to my original post. It is a bit technical, though I think most photographers should be able to follow it — and I will conclude with some simple, straightforward practical advice. (And here I remind readers that sharpness is not the most important, much less the only important thing in photography. Far from it!)

Sharpness, or at least the perception of sharpness, is a more complex thing than choosing the aperture the provides (to the extent that this can be determined) the highest optical resolution at the sensor plane, measured at either a) the best performing point in the frame, or b) the average across the frame.

(Speaking of “the extent that this can be determined,” I wonder how folks would answer the following question: Which is “sharper,” the image with the best center resolution but slightly lower corner resolution or the image with slightly less center resolution but better overall resolution across the frame?)

While we might consider whether f/16 will be softer than f/8 on some lens/camera combination — it almost certainly will be softer — it isn’t irrelevant to ask: “How much softer, and will this affect my print?” In quite a few cases the difference in maximum resolution in the print will be essentially invisible. In other words, while you will get optimal resolution at some particular aperture, you will actually still get extremely good print resolution at a smaller (or larger) aperture, too.

If there is no particular photographic reason to choose a smaller (or larger!) aperture, you might as well use whatever aperture you think will produce the highest resolution. That best resolution aperture will vary based on the lens you are using, the camera format, and arguably the photo site density of the sensor. To generalize, if you are shooting full frame it will probably be somewhere in the f/5.6-f/8 range with many lenses. (Other things can affect that — for example, what the maximum aperture of the lens is.) On a cropped sensor camera you could, in many cases, use either the same aperture or guess at one stop larger or so — while realizing that there could be resolution downsides to going larger with some lenses. Trade-offs abound! (I’ll spare you the technical discussion of all of the variables. You can think me later.)

But, seriously, if you are calculating the “sharpest” aperture to the closest 1/3-stop for each lens and using that aperture in the field and avoiding others that are slightly different, you probably aren’t really gaining anything significant from your efforts, and you may be sacrificing things that could make your photographs better.

That said, if we know that some mid-range aperture can provide the highest resolution, why use other apertures? And if we do use other apertures, won’t we end up with a softer print? Continue reading Photographic Myths And Platitudes — Diffraction Limited Aperture →

Photographs: New York City, Photographs: People

Americans

January 20, 2017 G Dan Mitchell Leave a comment

People in the street, New York City

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Photographs: Central California, Photographs: Flight, Photographs: Nature, Photographs: Wildlife

Twilight Birds

March 26, 2016 G Dan Mitchell Leave a comment

A flock of geese against twilight sky above the Central Valley

February was mostly a very good month for photographing migratory birds in the Central Valley this winter. This was a relief, quite honestly, after the past four years of drought and increasingly dire conditions in the Valley and throughout the state. In normal times, the wildlife refuges where I often photograph can be filled with water and life in the winter — flowing creeks and flooded fields where thousands of birds collect. But much of this water comes from sources that are not local, and as they dried up the refuges also began to shrink the acreage that was under water. It was sad to see locations that I’ve thought of as ponds become plain, dry fields. And at times the birds seemed to suffer a bit, too, or at least change their habits. Back in the late fall, before the course of the winter season became clear and Northern and Central California received rain again, we were concerned about what would happen this year.

But in most of California the rains came, at times heavy, and water flows once again. The birds returned, and sometimes it seemed that there numbers were exploding with the return of water. By February it wasn’t uncommon to find many thousands of birds in the refuges, and by late in the month the scene was downright wild, with all kinds of geese, huge numbers of cranes, and much more. In the evening things become active, and as the light fails I often continue to photograph, but at longer shutter speeds that allow me to work with the moving poetry of blurred birds in flight against dusk sky.

Photographs: Central California, Photographs: Nature, Photographs: Wildlife

Evening Geese

March 12, 2016 G Dan Mitchell Leave a comment

A large flock of geese takes to the air in evening light

Each day among these migratory birds moves through a kind of cycle, with variations that eventually become familiar but which don’t become any less compelling or exciting. It typically starts with a pre-dawn drive and arrival at a likely spot to find them — preferably in fog! It is always thrilling to catch the first sight and sound of the birds. The day continues, likely passing from fog to hazy sunshine, as the birds tend to settle into midday routines. Sometime after lunch it is (almost always) time for a break, but the work resumes by mid-afternoon. At first things happen slowly, but as evening approaches the pace picks up – more birds coming and going, more frequent take-offs, light that evolves in beautiful ways — and before long it is sunset and then dusk.

Early morning and evening are times of daily transition for the birds, so there is often a lot of action. Although a mass take-off can occur at almost any time if something sets off the flock, they become more likely and more impressive in the evening. They also become more difficult to photograph! As light fades and the subject becomes more interesting, the photographic challenges of low light increase. Rather than giving in to the dimming light I often take a different approach and embrace the motion blur, following the general mass of birds but allowing the fine details to soften and merge.

G Dan Mitchell Photography

Tag Archives: blur

Photographic Myths And Platitudes — Diffraction Limited Aperture

Americans

Twilight Birds

Evening Geese

Photographer and visual opportunist. Daily photos since 2005, plus articles, reviews, news, and ideas.