Tag Archives: aperture

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 →

Morning Musings, Technique

Making Aperture Selection Easy (Morning Musing for 8/22/14)

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From time to time I see questions from photographers trying to figure out exactly which aperture is the “right” one for a particular photograph. Some will go so far as to consult depth of field calculators (or “DOF calculators”) to help them decide whether the should open up a third of a stop from f/11.

There may be times where that sort of precision aperture selection is useful, but in many cases you can make things a lot simpler*, basically selecting from one of three general options:

  1. If depth of field isn’t a big issue — let’s say you are shooting a relatively flat subject — simply use a “middle of the road” aperture that will be sharp on your lens/camera combination. The old rule of thumb about using f/8 is a decent one to follow here, although cropped sensor shooters might go for something more like f/5.6.
  2. If you need very deep depth of field, go straight to the smallest aperture you feel comfortable using. On a full frame camera this is likely to be about f/16, while on a cropped sensor camera it might be a bit larger, perhaps in the f/11 or so range. If your need for extra deep depth of field is strong enough that you are willing to give up a small degree of overall image sharpness — which will be invisible in small images anyway —  you might even go one stop smaller on some occasions to f/22 on full frame and f/16 on crop.
  3. If you need to limit depth of field to throw background elements out of focus, simply try the largest aperture that your lens has — but consider stopping down just a bit if you need just a bit more depth of field.

Basically, for most photographs, especially if you have good light and/or are using a tripod, you could probably get away with considering only three apertures in most cases — the “normal” one, the really small one, and the really big one.

  • Yes, this is a bit of a simplification, though it really does work in the vast majority of the photographs that most people are making. Clearly things can get a bit more complicated if you are, for example, shooting in very low light or need to deal with moving subjects. In the interest of keeping this “Easy” description easy, I’ll simply acknowledge those possibilities here without elaborating.

G Dan Mitchell is a California photographer and visual opportunist whose subjects include the Pacific coast, redwood forests, central California oak/grasslands, the Sierra Nevada, California deserts, urban landscapes, night photography, and more.
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Text, photographs, and other media are © Copyright G Dan Mitchell (or others when indicated) and are not in the public domain and may not be used on websites, blogs, or in other media without advance permission from G Dan Mitchell.

Equipment, Technique

Some Thoughts on Aperture and DOF and Related Issues

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(This post is slightly adapted from something I recently posted in a photography forum in which hyperfocal distance, “DOF calculation” software, and related issues were under discussion.)

Shooting as a way to learn to understand how things like depth of field or “hyperfocal distance” work is a great idea – it is perhaps the best way to understand these concepts. I firmly believe that it is better than relying on tools such as software DOF (“depth of field”) calculators or tables. Fortunately, it is easy to do some basic experiments related to aperture and DOF and the so-called hyperfocal distance.

(The term hyperfocal distance can be interpreted in a couple of ways. In photography, this is often thought of as the distance at which you might focus in order to place objects at different distances in focus. If there is an object that is 15 feet from the camera and there are important subjects at infinity, the hyperfocal distance lies beyond the object that is 15 feet away and closer than the far away objects that might be in focus with the lens set to “infinity.”)

To find out about the effect of aperture on DOF, try the following:

  1. Put the camera on a tripod and compose some reasonable test image that includes subjects at various distances from the camera position, with a primary subject somewhere between the closest and the furthest.
  2. Focus on your primary subject within the scene.
  3. Shoot a series of images at apertures ranging from the largest to perhaps f/16 – shoot at f/1.4, f/2, f/2.8, etc. You might want to go as far as f/22 on full frame.*
  4. If you want to be a bit more methodical, you can use your DOF tables/software to “calculate” your hyperfocal distance, focus there, and repeat the process – but, frankly, I wouldn’t bother.
  5. Spend some time – likely well under an hour – looking over the results on your computer. If possible, make a few small prints to confirm the relevance (or not) of what you observe on the screen.

Another great way to understand the effect of aperture on the depth of field in your shot is to shoot in live view mode on your DSLR. Here you can press the DOF preview button, zoom in the live view display to 5x or 10x magnification, and pan around the magnified image on the rear display to see a very good approximation of the effect of your aperture choice on elements of the scene at various distances from the camera.

SIMPLIFICATION: A SECRET

Let me share a little secret. From reading some photography forum posts, you might get the idea that lots of photographers are going around making careful and technical calculations of precise hyperfocal distance and DOF and all the rest and then making exactingly accurate choices about aperture for each shot. In general, it doesn’t work that way in the real world, where photographers often tend to select aperture in basically three ways:

  1. In a shot where the subject doesn’t have a lot of depth and DOF isn’t really an issue, we tend to shoot at some default aperture that we believe is more or less optimal for overall resolution, corner resolution, and perhaps vignetting. On full frame, this might frequently be roughly f/8, though there are reasons to vary from that a bit sometimes.
  2. When working a subject on which we want very large DOF, we tend to go straight to the smallest aperture that we feel will produce large DOF and very good resolution. For me, this is typically f/16 on full frame, it might be no smaller than f/11 on cropped sensor cameras. There are situations in which I might use a smaller aperture, but they are very rare and will involve acceptance of some tradeoffs.
  3. When faced with a shot in which we want very narrow DOF, we tend to open up as much as we think we can, perhaps tending toward the largest aperture on the lens we are using. There are some additional factors to consider here, but I’ll leave them out for now in the spirit of simplifying.

So, a simple generalized approach:

  • Shoot at some middle-of-the-road aperture when DOF isn’t a major concern.
  • Shoot at the smallest acceptable aperture when you want large DOF – f/16 on full-frame or f/8-f/11 on crop.
  • Open way up when you want to minimize DOF.

This approach works in a wide range of real-world photographic situations, and it is especially useful to begin with it when you have to work quickly. There will be situations in which these are simply starting points, and you’ll need to make some modifications – for example, in very low light you might not be able to use that very small aperture if you are shooting hand-held, or your largest aperture might produce DOF that is too narrow for some subjects, and so on. But starting with this simple basic concept, using live view DOF preview when appropriate, and learning from experience will likely move you a lot further along on the road towards understanding and making effective use of aperture/DOF than trying to rely on some DOF calculator. (Depite their appearance of accuracy, these calculators depend on a bunch of assumptions that may not match up with your photography.)

* You can stop down further on cameras with larger sensors before you run into issues with diffraction blur, a softening of the overall image that occurs with the smallest apertures. To generalize, while you can stop down to roughly f/16 on a full frame and still produce very sharp images, you might want to avoid such a small aperture on your cropped sensor DSLR, perhaps avoiding anything smaller than about f/11… and you might want to be a bit cautious about using f/11.

© Copyright 2012 G Dan Mitchell – all rights reserved.

G Dan Mitchell is a California photographer whose subjects include the Pacific coast, redwood forests, central California oak/grasslands, the Sierra Nevada, California deserts, urban landscapes, night photography, and more.
Blog | About | Flickr | Twitter | Facebook | Google+ | 500px.com | LinkedIn | Email

Text, photographs, and other media are © Copyright G Dan Mitchell (or others when indicated) and are not in the public domain and may not be used on websites, blogs, or in other media without advance permission from G Dan Mitchell.

Commentary

Thought I found a photo contest with fair terms… but only for a moment

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(Update 7/7/11: After posting a link to this old 2009 post I realized that not all of the original links are still live. Rather than start modifying the following post, I will leave it as it was written, even though access to the original posted source material may no longer be possible. Aside from the specific contest – which is long since over – and any individual involved in it, the general lesson is that it is critical to read contest terms carefully before you decide to enter.)

(Update: I just receive a, uh, “personal” email from the contest promoter. I won’t share the content of that message here at this point, but I did write what I think was a very civilized email in reply,  I offered “Scott” the opportunity to post a response here as a comment, and I offered to correct any “false statements” in my post.)

(Update #2: “Jeff” says that that I was apparently incorrect about the lack of contest terms assigning legal liability to entrants: See these terms. This longer “terms” page also includes names of “vendor sponsors” who also have acquired rights to use submitted work.)

I’ve recently posted a few times on what I and others refer to as intellectual property rights grabs masquerading as photography contests. (For example, see this post describing unethical terms in contests presented by the Sierra Club and by Costco.) The short story is that entrants (not just winners!) in these contests agree to provide to the contest organizers and typically a whole range of their associates) a cost-free, unlimited, perpetual license to use their entered photographs in essentially any way imaginable (and some contest specify that even currently unimaginable methods are included!) without any compensation, credit, or control – and many additionally assign to the entrant full legal and financial liability for the use of the photograph.

Just because one enters the contest. That’s right. If you enter and lose – and the odds are that you will lose – you are fully subject to the contest terms. Continue reading Thought I found a photo contest with fair terms… but only for a moment →