Testing Lenses: The Brick Wall Test

Today’s Post by Joe Farace

I was never a the kind of photographer that would test lenses by shooting a resolution chart like the classic 1951 USAF resolution test chart whose longevity shows that, as Jean-Baptiste Alphonse Karr, once said, “the more things change the more they stay the same.”

I never even shot the ‘poor mans’ resolution chart; taping a sheet of newspaper to the wall and shooting that. But I am a fan of shooting a brick wall but not so I can brag about how great the camera/lens is 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 asks, “well, how sharp is that lens,” I can tell them how it went with a brick wall test. I typically do a Brick Wall Test for sharpness but you can also check for distortion and vignetting.

 brickwall

With a good lens, corner sharpness should increase as a lens is stopped down. Barrel distortion causes the edges of the image to bend outward and pincushion distortion causes the edges of the image to bow inward, all of which is easy to see by the alignment of the mortar in bricks in your final photograph. 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 corners of his prints to focus the viewer’s attention on the subject.

And don’t forget that all lenses have a “sweet spot,” which is the aperture at which it’s sharpest. The general rule is that a lens’ sweet spot is usually in the mid-range apertures between two and three stops down from the smallest aperture. Or you can find that sweet sport by shooting a brick wall at various apertures.

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 at different apertures and if it’s a zoom lens, shoot at different focal lengths. Then blow the shots up to fill your monitor, checking sharpness in the center and edges using the Loupe tool built into Adobe Photoshop.  The other aberrations should stand out clearly enough, again depending on how well the bricks were laid. Or you can do what I usually do: Don’t worry about it and just have fun with your photography.