Today’s Post by Joe Farace
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 big fan of shooting a brick wall but not so I that can brag about how great or bad a lens is at the camera club or on on-line forums. I have successfully been using this kind of test with all the lenses I reviewed in the former print edition of Shutterbug but also when I get a new lens for my personal use. With lenses for my personal use or thumbnails reviews on this site, when people attending one of my PhotoWalks 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 too. Not just to test for sharpness but also use it to check for distortion and vignetting. With a good lens, edge 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 with the alignment of the mortar in a well-placed rows of brick. Vignetting, which is also affected by aperture, can show a gradual darkening towards the image’s corners, which is not all that bad or portraiture and even Ansel Adams burned the four-corners of his prints to focus the viewer’s attention to the subject. But like everything else in photography, I think that it’s your call if this is a good or bad thing. But I have tested lenses for Shutterbug where the vignetting was different on different edges of the frame.
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 it 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 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.
If you would like to see the actual wall of bricks I use for my testing and Shutterbug lens reviews, I’ll be sponsoring a free Photowalk in downtown Parker sometime this summer and part of the walk will take us past that very wall.
If you enjoyed today’s blog post and would like to buy Joe a cup of Earl Grey tea ($2.50), click here. And if you do, thank so very much.
Barry Staver and Joe Farace are co-authors of Better Available Light Digital Photography that’s currently out-of-print but new copies are from Amazon for $21.88 and used copies starting at $4.09, as I write this, which seems like a bargain to me.