Joecosentino Loc: Whitesboro, New York

Print a test pattern and shoot it under good light a several f stops, in most cases with newer lenses my guess is it won't be much of an issue. If you have a lens that is shoot for the crop and crop out the softness

mikegreenwald Loc: Illinois

Right on! Brick walls are ubiquitous and free, and you don't need a model release! Look out for uniform lighting, and use a tripod for a sensitive test.

Retina Loc: Near Charleston,SC

If I were choosing among lenses for certain types of shooting where corner sharpness really mattered, I would naturally focus the test subject in its corner(s). Conversely, when assessing center sharpness, would you mainly focus for the corners and then see how the center does?

jcboy3

With a single exposure, you want to focus in the corner. That will let you know whether that particular corner is sharp, in and of itself. You will need 4 exposures (one for each corner) to assess overall corner sharpness. Then, you will need one exposure focussed in the center, to determine whether the corners are in focus when the center is in focus.

ORpilot Loc: Prineville, Or

👍🏻👍🏻👍🏻. We used a newspaper to test our lenses ot Ohio University Photo Department. It worked in 1971 it should still work today.

tinplater Loc: Scottsdale, AZ

Again, what bothers me is a lens is pronounced "soft in the corners" (this is a frequent occurence) when one would almost expect that to be the case because the corners are farther away from lens center than the center of the image. How one quantifies this is beyond me? Focal length and distance from the object clearly come into play as well.

rgrenaderphoto Loc: Hollywood, CA

So, for a 24 mm lens, that would be 480 feet? Seriously?

mwsilvers Loc: Central New Jersey

That's a piece of cake. I could just set up a target at the other end of my basement.

therwol Loc: USA

Okay. Math answer. 24mm x 26= 624mm = 62.4 cm = 24.6 INCHES (approx).

John_F Loc: Minneapolis, MN

I bungled. Where I wrote "focus" I meant "field".

Several have written that the corners are somewhat further distant than the center. It is true that the actual distance of the corners is greater than rhe perpendicular distance, but those are not the optical distances. Every lens has central axis on which the origin of the radii of curvature of all lens surfaces lie. Every lens has 4 cardinal optical planes: two principal planes and two focal planes, one for lens front and one for lens rear, the distance between the principal and focal planes is the focal length - these planes are mathematical constructs. Subject distances are conveniently measured from the front principal plane so one doesn't have to deal with negative numbers. If you set your lens to 10 feet there will be an optical plane at 10 feet in which everything will be in focus. If the lens optic axis is perpendicular to the wall, the entire wall will be in focus. Of course, depth of focus comes into play if the wall is not perfectly flat. Some lenses do show corner softness and this arises from lens elements are not perfectly spherical.

Retina Loc: Near Charleston,SC

Nature sure was smart when she decided on a curved eyeball.

wdross Loc: Castle Rock, Colorado

I would use a newspaper on a wall and use the camera's leveling system. Focus at the middle of the newspaper, take a shot, and examine the corners for chromatic aberration, distortion, etc. Change the aperture and shoot again. Examine the corners again. Continue until you have satisfied your interest. Lenses are designed for a relatively flat plane at the point of focus. The corners may be better in-focus a little in front or a little behind that center focus point but should be of relative insignificant especially compared to the subject of interest in the main part of the frame.

Jim Bob

Shoot a flat object wide open.

tinplater Loc: Scottsdale, AZ

Thanks for the information...unfortunately math and I do not get along well. I wish I could meet with you in Mickey's Diner, share a heart attack on a plate, and have you tutor me through this. But if I understand you, a lens should be able to have corners exactly as sharp as the center despite being at different distances from the sensor?

therwol Loc: USA

The problem with some lenses, and I have one, is that the corners may remain soft at any f/stop. Also, many lenses, particularly older designs, sharpen up considerably after being stopped down a bit. The wide open test is only valid if you plan to shoot wide open.