[ssfrr]

> an error of even 1/8 mm in the placement of the camera would result in a useless image.

That doesn’t make sense to me. Presumably part of the image stitching process is aligning the images to each other based on the areas they overlap, so why do they need that much precision in the camera placement? I’d think keeping the camera square to the painting would be important to minimize needing to skew the images, but that doesn’t seem to be what they’re talking about.

[gertlex]

I assumed it was mostly distance from painting surface to camera that needed to be controlled for.

[schobi]

A camera+lens set up to 5 micron/pixel will have a shallow depth of field.

I looked up some numbers: The pixels of the camera are 4.6um, so the likely used a 1:1 makro lens (likely the HC 4/120mm). You will capture a 53x40mm region at once. The working distance for this lens goes down to 40cm for 1:1 magnification (might have been 40-45cm). Aperture 4 (as little diffraction as possible)

If we put that in a calculator, depth of field is only 240um. This is the working range where the object needs to be to be in focus.

I'm surprised the painting is that flat over a single image. Even a high spot on the canvas or an extra dab of paint will be higher. Maybe they took multiple images and focus stacked them?

[ipsum2]

The camera is manual focused, so 1/8mm would make it out of focus.