Q about 'macro' camera settings

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Here are some results. Please forgive the lighting, I'm just trying to show distortion correction method #1 from my previous post.

Actually the Luger pistol design tends to understate barrel distortion because the top silhouette of the pistol is very busy, broken up with receiver, toggle, toggle knobs etc. The barrel exhibits visible bend in the top photo, when shown at the top of the frame. In the second photo it is straighter. You can actually lay a ruler on the photos using three reference marks like the front sight and bottom of the toggle and safety lever, and measure less bend in the second photo. While the "straight" picture is not perfect, it actually illustrates another important technique - if you want one good photo, take many more (20?) from various positions, then pick the best. I just took just two pictures to make my point.