Category Archives: Equipment

Equipment, Popular, Technique, Tests

Sharpness and Aperture Selection on Full-Frame DSLRs

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(Note: This article was originally posted in 2007 and I should probably update the test using newer gear – though the point of the test and the post remains.)

Last month I wrote about a set of tests (“Full Frame Lens Test“) that I conducted with my lenses and my Canon 5D body. My object was simply to better understand how the camera/lens combinations would behave so that I could make better decisions about appropriate lenses and apertures while making photographs.

One discovery was that, compared to using a crop sensor DSLR, I can get excellent results when I shoot at smaller apertures with good lenses on the full frame body. I tended to avoid apertures smaller than about f/8 on the crop sensor camera, but there seems to be little or no real liability in using f/11 or even f/16 on full frame.

To illustrate I put together the following composite image. (The image appears in reduced form on this page. Click the link to see the full size version.)

Diffraction Blur Test Image
A sequence of text photographs illustrating diffraction blur at several apertures on a full frame camera

The example includes five versions of a small section from near the center of a photograph taken with the Canon EOS 5D using the EF 24-105mm L IS lens at a 50mm focal length. The camera was on a tripod, MLU and a remote release were used, and the AF was turned off. The images are 100% crops – in other words, actual pixel size is displayed in these tiny excepts from the much larger original images. (You would virtually never view a print at this magnification. These are equivalent to tiny sections from a print that might be about 5 feet wide!) The images have been slightly sharpened in post-processing, but are otherwise unaltered.

I shot at apertures of f/4, f/5.6, f/8, f/11, and f/16. In terms of the sharpness of this portion of the image, I am quite certain that all five examples are plenty sharp for making prints. That said, there are some differences. To my eye:

  • The f/4 and, to some extent, the f/5.6 versions are slightly but noticeably softer at this magnification.
  • The f/8 and f/11 versions seem to me to have approximately equal sharpness. Some parts of the f/8 image seem slightly sharper, but other parts of the f/11 image seem sharper. In the end they are pretty darn equivalent, though I’d maybe give the f/11 a very slight edge overall.
  • The f/16 image may be slightly less sharp than the f/8 and f/11 versions, but the difference would not be noticeable in a print, even a rather large one. In any case, f/16 appears sharper than either f/4 or f/5.6.

After doing this test I no longer hesitate to shoot at f/11 or f/16. Not only does this give me the possibility of getting greater depth of field when I need it, but it also means that I can compensate for corner softness on some lenses (e.g. the 17-40mm) by using a smaller aperture without fear of losing center sharpness.

(Addition: 4/23/07 – Other Canon L lenses seem to give similar results, including my 17-40mm f/4 L and my 70-200mm f/4 L.)

Added 2/23/08:

In response to a question in a photo forum I put together a sample image showing corner sharpness from the same original images used in the example above. (The earlier example shows 100% crops from near the center of the frame.)

(image temporarily unavailable) Canon 24-105mm f/4 L IS lens corner sharpness test

Technical info: Shot using a Canon 5D with the Canon EF 24-105mm f/4 L IS lens at a 50mm focal length. In aperture priority mode, the aperture was changed manually between shots. Initial focus was with AF, which was then switched off before shooting the series. Camera was on a tripod and MLU and remote release were used. Shots were converted from RAW with ACR and no additional post-processing applied. Print made at this resolution would be approximately five feet wide. The crop is from the far lower left corner of the frame.

In addition to noting the softer image in the corner at f/4, also note that the image is a bit darker due to the expected increase in corner light fall-off (“vignetting”) at the largest aperture. Sharpest version in this series shot with a FF body seems to be at f/11 as in the center crop example above. But note that f/8, f/11, and f/16 are not very different in overall sharpness – and in the end any of these apertures would produce a very sharp print.

In response to another forum discussion, I have added another example, this time using the Canon EF 50mm f/1.4 lens and showing performance at f/5.6, f/8, f/11, and f/16. In other respects the test is the same as described already in this post. This image is seen to the right and below.

(image temporarily unavailable)

Conclusions: Based on this set of images and other taken with different lenses under similar conditions, I have come to some conclusions that work for me with my Canon lenses and full-frame Canon 5D body.

  • In general the sharpest whole aperture seems to be around f/11.
  • It is very difficult to distinguish any resolution differences at f/8 or f/16 – there are subtle differences when viewing the test images at 100% magnification on my monitor but these are essentially invisible in prints.
  • f/5.6 or f/22 will tend to be a bit less sharp, though perhaps not for the same reasons. At f/5.6 I begin to notice a bit more of the diminished sharpness as a lens is opened up – more on some lenses than on others. At f/22 the effects of diffraction become just a bit more noticeable. However, if the shot demands it I do not hesitate (much) to use either of these apertures as the very slight decrease in sharpness is quite tiny if visible at all in a print and both provide some other advantages in certain situations. (I’ll even use the largest f/4 aperture on the test lens when isolating the subject is important or when low light demands it – and the results will typically be just fine.)
  • At larger apertures the performance becomes more tied to the particular lens so it is more difficult to make any generalizations beyond the fact that vignetting increases and sharpness will be less optimal.
  • The smaller apertures decrease any corner light fall-off (“vignetting”) or softness, generally to a point where both are insignificant.
  • With all of this in mind, unless I have a reason to select some other aperture I typically use f/11 as my general starting point when shooting with my full-frame DSLR body.

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.
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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

Death Valley: Equipment Observations

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I took some new gear on my recent Death Valley trip, including my Canon 5D and my Induro C313 tripod. Here are some reflections on this equipment after using it extensively for the first time:

Induro C313 Tripod – Last month I wrote about my quest for a new tripod to augment the smaller and lighter tripod I already own for backpacking and hiking. I had looked at the excellent Gitzo tripods and was probably headed toward purchasing one of those when I read Michael Reichmann’s review of the Induro C413, which was largely very positive. (He noted two issues, neither of which concerns me.) I was able to get my hands on several models at Keeble and Schuchat Photography in Palo Alto and was impressed with the quality of the tripods. Despite some concerns about buying a product with almost no track record, I finally picked up the C313 model.

THe C313 has large diameter three-section carbon fiber legs. With the legs fully extended, the center column all the way down, and with my Acratech ballhead attached, the camera is a few inches too tall for me to look through the viewfinder. This is about right since on uneven ground with some of the legs shortened the camera can still be at eye level. The legs have a welcome anti-rotation feature which makes setup a bit easier. The legs can be adjusted to three different angles to further accommodate uneven ground or to position the camera lower.

The good news is that there isn’t a lot to say about my experience with the tripod – it pretty much just worked effectively as expected. While not cheap it does cost a bit less than an equivalent Gitzo, and it seems to be to do the job just as well. Overall, I’m very pleased with the tripod.

Canon 5D – I acquired a used 5D about a month before this trip, so I have had some opportunities to use the camera and learn about its features and capabilities. Much of what I experienced on this trip confirmed what I have learned about it:

  • My lenses are capable of producing noticeably sharper images on this camera than on the 8MP 1.6x crop sensor DSLR. This is partly due to the somewhat higher number of photo-sites on this 12MP camera, but I think it is also because the photosites are larger.
  • The angle of view of a particular focal length is considerably wider on full frame. This was not a surprise. However, my 17-40 becomes a truly wide angle zoom on this camera – it was a “normal” wide to slight telephoto on the previous body. The 24-105 now seems to go equally far into the wide and telephoto ranges. I especially enjoyed working with the new wide angle capabilities of my 17-40.
  • Vignetting (darkening of the image corners) and corner softness are more apparent, especially with the 17-40mm lens, but with the 24-105mm as well. Shooting landscapes with wide expanses of sky at f/4 with either of these lenses leaves noticeable vignetting. Fortunately, for several reasons this turns out to be a fairly minor issue. I rarely do these sorts of shots wide open, and the issue largely goes away by f/8 – with the exception of some corner softness issues on the 17-40mm lens, but read on…
  • I can now use significantly smaller apertures. I would rarely shoot with smaller apertures than about f/8 on the crop sensor camera – at smaller apertures the increase in DOF was cancelled by the decrease in sharpness caused by didiffraction. However, I discovered before the trip that there was virtually no discernible decrease in sharpness at f/11 or even f/16 with the same lenses on the full frame 5D. I also found out that the corner issues, particularly on the 17-40mm lens, were essentially eliminated at the smaller apertures. Consequently I made great use of f/11 and f/16 on this lens and got great depth of field and sharpness that I could not have achieved with my previous camera.
  • Dust is an issue. I haven’t had the camera long enough to know if it is something about the 5D, shooting at smaller apertures, or just the fact that I was in one of the dustiest places in the world – oh, and I drove nearly 100 miles on dirt and gravel roads. However, I have some dust in every shot I took. Fortunately, cloning the dust spots out in Photoshop is not a big deal – and probably still a lot less trouble than retouching film would be!

One final observation. I kept my Canon 350D/XT body when I got the 5D. Being much smaller and lighter than the 5D it could be useful in situations where I don’t want to be saddled with bulky/heavy equipment, the crop sensor body gives me more “reach” with my longer lenses, and it could serve as a back up camera. I brought the camera along on the Death Valley trip.

My opinion of the 350D has not changed. I continue to maintain that this little camera is capable of making excellent images and that its small size and weight are advantages in many circumstances. I believe that it may well be one of those cameras that eventually comes to be regarded as something of a “classic.”

However… I didn’t even remove the 350D from the bag once on this trip. I’m rethinking its place in my equipment bag. While I might still use it on rare occasions, I don’t think that I’ll be inclined to forego the use of the 5D as often as I thought I might. I’m beginning to think about selling it…

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Equipment, Tests

Full Frame Lens Test

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I recently acquired a full frame camera body, and I’m interested in understanding more fully how my lenses work with it. Issues that interest me include:

  • How sharp is each lens on the full frame body?
  • How is sharpness affected at various focal lengths on zoom lenses?
  • What are the optimal apertures on each lens in terms of sharpness?
  • How does vignetting change at different apertures and focal lengths?
  • How is corner sharpness affected by aperture and focal length?
  • Are there significant differences between the performance levels of two lenses that have the same focal length?

Today I conducted an informal test. I wasn’t trying to find out if I have “good copies” of my lenses. Rather, my goal was to understand the “personality” of each lens a bit better. I can’t say I answered all of these questions, but I did come up with some interesting results, some of which confirmed what I expected and some that surprised me a bit.

The Canon lenses I tested are the EF 50mm f/1.4, the EF 17-40mm f/4L, the 24-105mm f/4 IS L, and the 70-200 f/4 L.

The test was simple – and I can’t claim scientific accuracy. I went to a familiar location nearby that features a ridge covered with grass and oak trees a few hundred yards away with closer grass, oak trees, a trail, and a fence in the mid-ground, and new grass in the foreground. I put the camera on a tripod, used mirror lockup, and a remote switch. I used auto-focus to pre-focus on the ridge, and then I turned AF off before shooting. With each lens, I then made a series of manual exposures at apertures ranging from f/4 to f/16 (slightly wider in one case). With zooms I repeated the test at the wide and tele ends and at one or two points in between.

I’m not going to post all of the results here, but I will share a few interesting things that I confirmed or discovered.

  • Overall, the lenses produce sharper images on the full frame body of my 12 MP Canon 5D. That said, the difference would probably not be noticeable unless you made a fairly large print.
  • All of the lenses vignette noticeably at their widest apertures and generally at one stop smaller. Vignetting was reduced to inconsequential levels in all cases by f/8 and in some cases sooner. (In any case, vignetting is not always a bad thing – just something to understand.)
  • I was surprised to see how well the lenses did at f/16. The common wisdom regarding diffraction (or the “circle of confusion”) is that lenses will be sharpest around f/8 or even a bit larger aperture, and that sharpness will degrade noticeably by f/16. Frankly, I just didn’t see that. There might be a little bit of degradation at f/16, but I have to look very hard for it in 100% crops. I’m more inclined to go ahead an use f/16 now in situations where I might previously have avoided it.
  • Not surprisingly, corner sharpness improves at smaller apertures. My 17-40mm has been soft enough on occasion that I’ve been compelled to crop off the edges of images. However, even this lens does quite well almost all the way to the corners at f/16 and it is better at f/11 than at f/8. An important factor is that I did not see any significant (as in “noticeable”) degradation of center sharpness when using the smaller apertures to get better corner sharpness. This is an important discovery – I think I’ll be much more likely to shoot the 17-40 at f/11 or even f/16 now.
  • I need to clean my sensor… :-) I had previously noticed a couple of spots that required post-processing removal in Photoshop when I shot at f/8. Such spots and even slightly smaller ones become more visible at the smaller apertures.
  • Good zooms are very sharp. While my 50mm f/1.4 prime is very good corner to corner at apertures like f/5.6 or f/8, the performance of the zooms is very close in almost all cases.

Some people get carried away with testing their lenses and trying to find the absolute perfect lens. That wasn’t my point. My goal was to understand the effect of my lens choices and to understand how to get the best image quality that these lenses can produce in a variety of situations. In that regard, I think this was a very valuable exercise.

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Equipment

Asking the Wrong Question – Part 1

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A type of question is frequently posted at photography discussion forums that goes something like this:

Help me decide. I’m going back and forth between the IS and non-IS versions of Canon’s f/2.8 or f/4 70-200mm zoom lenses, but I want to get the best optical quality. Which one should I choose?

Wrong question.

Too often the writer is trying to categorize really fine lenses into categories of “not good enough” and “best,” and on the basis of the wrong criteria in any case. Let me pursue this Canon lens example a bit. (You can probably substitute examples from the manufacturer of your gear.)

It turns out that all four of these lenses are optically excellent and can produce images of the equally high quality. They also share the same excellent build quality. Trying to decide between them on the basis of quality is hopeless. Any differences there might be – with the emphasis on might – are almost certainly much smaller than those based on normal sample variation.

And “quality” is really not the basis for distinguishing among them anyway. If you look beyond the issue of optical quality, there are other factors that likely are significantly different – though here what is “better” for one photographer may be “less good” for another. The significant variables among these lenses include maximum aperture, whether or not they have image stabilization, size, weight, cost, and how these factors make a particular lens more or less suitable for an individual photographer.

The best lens for someone requiring a zoom in this focal length range for handheld shooting of active subjects in low light would likely be the f/2.8 IS model. On the other hand, this could be a very poor choice for a landscape photographer who often carries the gear on the trail in a backpack and usually shoots relatively static subjects from a tripod. This photographer might be better served by the f/4 non-IS version.

The bottom line is that the significant differences between high-end lenses like these are not so much in their “quality” as they are in the “qualities” that they provide and their usefulness for ones particular approach to photography.

(One reason I’m writing this is so that I can point a link here rather than re-writing the message every time I want to reply to this question in one of those forums. :-)
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