Tag Archives: focus

Commentary, Equipment, Photographic Myths and Platitudes, Technique

Photographic Myths And Platitudes — Diffraction Limited Aperture

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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 →

Equipment, Technique, Tests

The Canon 5Ds R — Autofocus ‘Torture’ Test

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OK, “torture test” might be overstating things just a bit, but I’ve been meaning to check out a few things related to the capabilities of the autofocus system of my new Canon EOS 5DS R. A few years ago birds, especially winter migratory birds, became one of my photographic passions. While this camera is not really optimized for this sort of photography, I plan to use it for this purpose, as I did my 5DII.

The Landing
A brown pelican joins the flock on a rock along the Pacific coast of California

Most often when I photograph birds I use the Canon EF 100-400mm f/4.5-5.6L IS II lens. It usually provides enough reach for my purposes, it focuses accurately and quite quickly, it is sharp, and its flexibility fits my style of photography. (I often pause while photographing the birds and use the lens to photograph landscapes.)  It was my understanding that the 5Ds R added the capability to autofocus (AF) at smaller apertures down to f/8. This means that I should be able to add my Canon Extender EF 1.4x III tele-extender to get 560mm at f/8 from this lens.

A few days ago I was doing landscape/seascape photography along the Central California coast between lower Big Sur and San Francisco. On the final afternoon as we drove north we passed a small island where scores of brown pelicans had landed. Continue reading The Canon 5Ds R — Autofocus ‘Torture’ Test →

Equipment, Technique

Yet Another Reason to Like Live View – Shooting in the Wind

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I have posted in the past about some of the advantages of having a live view feature on your camera, especially for the types of photography that I do using my Canon 5DII. This past week I discovered another use, and an unexpected one at that – shooting in conditions of gusty winds.

I most often work from the tripod, and I usually use a pretty large and stable tripod in the context of shooting a full frame DSLR camera. But in some very windy conditions putting the camera on a tripod is not sufficient to stop camera motion and the consequent blur. This is especially a problem when you are shooting in low light or otherwise need to use very long exposure times, and it becomes worse when using long lenses which will catch more wind and magnify vibrations. There are a bunch of tricks that you can try in order to keep the camera steady, but in really strong winds the camera is just going to move, especially if you have a very large lens attached.

One way I try to deal with this is to time my exposures for moments when the wind may momentarily decrease. This can require a lot of patience – sometimes I’ve had to wait several minutes for a very brief halt to the gale, during which I try to make my exposure. But even in this case, you have to make sure that the camera vibration stops completely if you are using a long lens. Ultimately, you have to simply trust that the camera really has stabilized since there is no way to tell directly. Last week, as I was using live view to focus a 400mm lens on a distant subject and again noting that 400mm plus 10x software zoom in live view makes the camera very sensitive to vibration. In the past I have noted this mainly in the context of how darn hard it is to manually focus a big lens this way! But this time it occurred to me that I could use this in my favor.

With the 10x live view magnification enabled, the display is very sensitive to camera motion from the wind. I realized that by leaving the camera in the 10x magnification setup after composing the shot that I could simply watch this display, with its magnification of motion, and wait until the image stabilized during lulls in the wind to take my shots. If the display isn’t bouncing at 10x, motion blur is not going to be an issue. Problem solved. More or less.

G Dan Mitchell Photography
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Commentary, Equipment, Technique

Updated for 2010 – My Backpacking Photography Gear

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At about this time every year interest increases in the question of what equipment can work well for back-country photography. Over the years I’ve working out an approach that seems effective for my photography. A few years back I wrote an article here describing this, and I just made a few minor updates to it this morning. If you are interested, take a look at this description of my “Backpacking Photography Equipment.”

Keep in mind that my goals include making photography a primary focus of many of my back-country trips – so I’m perhaps will to endure a bigger load of gear than some might be willing to carry. Also keep in mind that I’m working to create photographs that can be turned into rather large and high quality prints – if your goals are more modest (and for most people, they should be!) you probably want to consider a somewhat different setup. Differences in your subject preferences – wildlife? macro? – might also suggest a different setup than I use.