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2026-04-23 "Field of Diamonds" Test of a Camera's Lens

I am sure some of you must wonder just how flat and sharp to the edges your camera’s images can be. I happen to find this flexible 8.25 x 12.25 cm (3.25 by 5 inch) plastic mesh of little reflectors. There are 24 on the long side and 16 on the short side for a total of 384 little reflective points.
I thought this might be a great test subject of flatness of field and distortion.
 

    Just to set some sort of baseline to actual testing I scanned the mesh at 200 dpi on a flatbed scanner. It will demonstrate the exact sharpness you can get having an object exactly square to the lens (of the scanner). It sets a very high bar, unless you happen to have a copy stand, because exactly setting the mesh up with the lens exactly centered and parallel with the camera’s sensor is a huge part of the battle.
    I used my FujiFilm Z10 family camera. It isn’t much to write home about as a camera, being a consumer point-and-shoot with 3x internal zoom, 7 Meg files and some signs it has barrel distortion in the wide zoom end it opens with. I set the camera up on a small Velbon tabletop tripod that looks like a tube with three wide-spread feet and a ball head on the top (you will be seeing the tripod's feet in some shots).
    Knowing the problem with barrel distortion—and the problem the tripod was too high to get the mesh subject close enough to fill the frame—I tried this compromise. I tried to square the top of the frame and the right side and let the other two sides fall where they would. I was pretty impressed with how close to the flatbed scan results this camera could produce.



(above)This is the same shot as before, just cropped so the mesh fills the frame edge-to-edge. We will return to comparing the center and corner at the end.


Figuring I should try zooming in until the mesh filled the frame. The mesh is not exactly square as the small plastic connectors distort a bit. Still, the corners rival the center.


In an attempt to be fair to Fuji I zoomed the lens all the way out—all the shots were taken in “Macro” mode—just so you might see the aforementioned barrel distortion. Is it just me, or does the center of each side seem ballooned out (as in the definition of barrel distortion. 

This is the last shot cropped tight using the left edge as a straight edge. The right edge seems pretty square too, but the top bows down and the bottom bows up.

    Taking a bite out of the previous cropped image, this is the center sharpness.











    And this is the corner sharpness (give or take a row or column to get the same number of reflectors). 
    Of course you don’t need a mesh of reflectors to play with testing. Anything from a chess/checker board to a block wall can be shot for testing purposes. But once you start testing, you face the testing conditions can influence the results. Changing illumination, changing of the steadiness of the support, changing subjects (high contrast/low contrast), changing focus (one place autofocus can vary)…it can be a never ending challenge.

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