“The more things change the more they stay the same.”—Jean-Baptiste Alphonse Karr
I was never a guy to shoot lens tests using a resolution chart such as the classic 1951 USAF resolution test chart. I never even shot the ‘poor mans’ resolution chart” by taping a sheet of newspaper to the wall and shooting that. But I am a fan of shooting a brick wall test but not so I that can brag about it at the camera club or for posting on-line forums. Invariably if I get a new lens and a group of photographers are attending one of our PhotoWalks or Coffee & Cameras events and ask, “well, how sharp is that lens,” I can tell them how it went with my brick wall test.
You can use the Brick Wall Test not just for sharpness but also use it to check for distortion and vignetting. With a good lens, sharpness should increase as a lens is stopped down. Barrel distortion causes the edges of the image to bend outward and pin cushion distortion causes the edges of the image to bow inward, all of which is easy to see in a photograph of the alignment of the mortar in a well-placed rows of brick. Vignetting, which is affected by aperture, shows a gradual darkening towards the image’s corners, which for portraiture is not all that bad and even Ansel Adams burned the four-corners of his prints to focus the viewer’s attention on the subject. But like everything is photography—it’s your call.
So if you pick up a used lens and want to see how much of a bargain it really is, go shoot a brick wall test at different apertures and if it’s a zoom lens, shoot at different focal lengths too. Then blow the shots up to fill your monitor, checking the sharpness in the center and edges. The Loupe tool that’s built into Adobe Photoshop/Bridge works pretty good for this too. The other aberrations should stand out clearly enough, again depending on how well the courses of bricks were laid.
PS: If you would like to see th7e actual wall of bricks I used for my testing and also for lens reviews in Shutterbug, I’ll be sponsoring a free Photowalk sometime after Labor Day and part of the walk will take us past that very wall.
Barry Staver and Joe Farace are co-authors of Better Available Light Digital Photography that’s currently out-of-print but while new copies are available at collector (high) prices, as I write this you can purchase used softback copies for seven bucks from Amazon.