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Do It Yourself Lens Testing
Jim Doty, Jr.

Lens testing can be as simple or complex as you want to make it. If you prefer not to do any testing yourself, there are several printed and online sources for lens tests.
 

Online Lens Reviews

Popular Photography magazine regularly tests lenses.  Their results generally agree with my own assessments of the lenses which I have used. I consider them to be good general guides to the overall quality of the lenses they test. They will occasionally publish a list of all of the lenses they have tested. For a small charge, they will send you a copy of any lens test they have done. You can also search for lens tests at their Web site. 

Another site with good lens reviews is Photozone. Photodo also has a set of lens tests. With their permission, I have published a summary of their test results on this site, including some lenses they have tested in the past that are no longer listed on their site.
 

Why Test Your Own Lenses?

As valuable as printed and online tests are, it's not quite the same as testing your own lenses. Although manufacturing consistency is generally good, occasionally a bad version of a good lens slips through. Some professional photographers used to buy 4 or 5 copies of the same exact model of lens, test them all, keep the best, and return the rest of a refund. Although not going to that extreme, I did buy a lens that seemed lacking in quality. I tested it against another lens I knew to be sharp, confirmed my suspicions, returned it, and bought another lens which I also tested. It was great.

Some photographers test their own lenses to answer any nagging questions they may have.  Which of my lenses are the sharpest? Which apertures are the best for each of my lenses? Which lens works best in demanding situations (like shooting into the sun)?  Did I get a bad copy of a lens that is usually quite good in quality?  Some people like to test their lenses just for the fun of it. Whatever the reasons, there are several ways to check the quality of your own lenses.
 

The Brick Wall Test

If you want to test your own lenses, you can start with simple tests.  Pick a brick wall with lots of texture and photograph it when there is good directional side light on the wall. Put your camera on a tripod and photograph the wall. Set your digital camera to ISO 100 and its highest resolution, or use high resolution slide film like Fuji Velvia. Keep track of the lenses and apertures used so you will know which photos went with which lens an aperture.  One way to do this is to tape note cards to the wall indicating the lens, focal length and aperture that were used for that photo.

Compare your digital files at 100% (actual pixels) resolution on your monitor to check the recording of fine details (with film, look at your slides through a loupe or small microscope) and ask yourself how sharp the images look.

Then view the whole photo on screen. Are the lines straight or do they bow in (pincushion distortion) or bow out (barrel distortion)?  This is where the brick wall test really shines. Compare different lenses at the same aperture or the same lens at different apertures.
 

The Newspaper Test

For a more demanding test of resolution, tape up a sheet of newspaper want ads with a variety of type sizes.  Pick a distance standard for comparing lenses, like one inch of distance for every mm of lens focal length.  If you are testing a 50mm lens, the camera should be 50 inches from the newspaper. With a 200mm lens, the camera should be 200 inches from the newspaper.

Once again, compare your your digital files at 100% (actual pixels) resolution (or check your slides with a loupe). How small a type size can the lens resolve? Compare results to other lenses you own. Which are your sharper lenses? What are the sharpest apertures?
 

USAF Lens Testing

The most rigorous do it yourself lens testing that is readily available is to do lens testing with a USAF Lens Testing Chart. All of the details are at the USAF lens testing page.
 

Flare, Ghosting, and Color Fringing

To check for flare, pick a clear, blue sky day with no haze. Hold up your hand at arm's length and hide the sun behind your thumb. If you see blue sky around the edges of your thumb, you have the right kind of day. If the sky around your thumb is bright and hazy, it isn't the right kind of day. 

Take a picture with the sun in the middle of the frame (meter for blue sky away from the sun). Try different apertures. Then take more pictures with the sun farther and farther away from the center of the frame (again with different apertures) until the sun is at the edge of the frame.  You may see one or more ghost images of the sun in the photos. This isn't unusual.

If the overall look of the image is soft or hazy, you have flare. Take a picture with the sun in the corner of the frame. Then take the same picture but block the sun with your hand so that no direct sunlight hits the lens (you will see your hand in the photo).  If the second photo looks crisper, more defined, and with better color, the first photo is suffering from flare (kind of like driving into the sun with a dirty windshield as compared to a clean windshield).

Facing the sun, photograph a tree without leaves in the winter (or a dead tree in the summer) and hide the sun behind the trunk of the tree (use different apertures).  Or photograph a power pole with a lot of power lines and hide the sun behind the pole. Look at the edges of the small branches (or the power lines) and see if they have colored edges (often blue or purple). This is color fringing. Some lenses are worse than others. Color fringing can be corrected with the right kind of software.
 

What Results Should You Expect?

In terms of resolution, most lenses are sharpest around their middle apertures like f/8.  Any aberrations in the design of a lens show up most at the widest apertures like f/4 for zooms and f/2 or f/2.8 in single focal length lenses. All lenses lose sharpness at the smaller apertures (f/22 or f/32) due to diffraction (the bending of light rays as they pass through the small aperture opening).

Telephoto zoom lenses are usually sharper in the middle or the short end of their focal length range.  If you have an 80-200 zoom, it is likely to be sharpest at 80 and 135mm, and less sharp at 200mm.  This means if you have a 28-100mm zoom lens and a 100-300mm zoom lens, the 100-300mm will probably be sharper at 100mm than the 28-100mm is at 100mm.

Wide angle zoom lenses are usually sharpest and the medium and long end of their focal length range. At 10-22mm zoom lens will probably be sharpest at 15 and 22mm and less sharp at 10mm.

Some lenses are the exception to the rule. A little testing will show you how your lenses fit into the general scheme of things.

When it comes to lenses, you get what you pay for - sort of. A $400 zoom lens may be a lot sharper than a $150 zoom lens of the same focal length range. A $1000 zoom lens may be only slightly sharper than the $400 zoom. The $1000 buys you a faster maximum aperture (like f/2.8 as opposed to f/4) but it won't necessarily buy you a lot more sharpness than the $400 zoom lens.  Some inexpensive prime (single focal length) lenses, like the 50mm f/2 or 50mm f/1.8 lenses that sell for $100 - $150 are usually sharper at 50mm than very expensive zoom lenses that have 50mm in their zoom range. Given a choice between a prime 50mm lens and a 28-105mm lens at 50mm, the prime lens will alsmost always be sharper. Although the gap has narrowed significantly, prime lenses are usually sharper than zoom lenses. Zooms are popular because they are so convenient and they have increased so much in quality.

If a manufacturer offers three similar zoom lenses in different prices, the middle priced lens is usually you best value for the dollar, UNLESS you happen to need the faster maximum aperture of the high dollar lens.

When it comes to ghosting, flare and color fringing, lenses vary quite a bit. Zoom lenses are usually worse than prime lenses due to their complex designs. There are exceptions. Some lenses do quite well when shooting toward the sun, and some don't. Testing will tell you which of your lenses does the best job in demanding circumstances. For example, if your 24-105mm lens has a lot of flare at 30-40mm, and your 17-40mm lens has minimal flare at 30-40mm, whenever you shoot toward the sun in that focal length range, use the 17-40mm lens.

Lens Testing with the USAF Chart

If you are using a digital camera and would like a more detailed, technical, and computer based kind of lens testing, check out Norman Koren's Imatest.

Nov 20, 2000
Updated Feb 18, 2011

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