Full frame of US currency isn't exactly a stringent standard. Here's my regular, plain iPhone 12. Pardon my scribbles on it-I think there are actually some legal issues with reproducing full frame US currency, and Photoshop will throw up an error message and refuse to open if you try to do it. I was going to blur SN and "legal tender" text in PS, but no go on that...
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Here's as close as I could focus with my iPhone
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With that said, if you really want to push the limits of close up, there are still far better tools. This is nothing too exotic-just a macro lens on a DSLR(camera reviewers tend to love currency because there's so much detail).
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This is actually not a full resolution file. Apparently I'd set the camera to a 1:1 crop without realizing it, and also I resized this to 4000x4000 pixels to meet upload limits here(original is 5504x5504 pixels). This is uncropped other than what I inadvertently did in camera.
This, BTW, is a 1:1 magnification photo, or in other words what you're actually seeing is a 24mmx24mm(roughly 1"x1") area of the bill. If I'd printed the original file at 72dpi, it would have printed to around 77 inches.
If you're interested in equipment for the above, it's a Nikon D850 with a 55mm f/2.8 AI-S Micro-NIKKOR(not my favorite lens, but acceptable and what I had handy) paired with a PK-13 27.5mm extension tube. This was shot at an effective aperture of f/64(f/32 on the lens) and under my Norman strobes. I should have used a larger aperture as this was pretty underexposed. This could also be a lot sharper-diffraction kills lens performance at apertures this small even though these macro lenses are crazy sharp as a general rule. BTW, this was handheld...