Using a 15" screen as a reference for magnification is understandable from the company history but does not relate to just about any other defined magnification typically used. Magnification is generally the purely optical magnification of a projected image - in this case how large the projection of that FOV of 3mm would be on your sensor.emilien wrote: ↑Thu Nov 23, 2023 3:05 pm
In this case, at 90x we have a pixel size of about 1.3 um and a horizontal FOV of approximately 3 mm for 2500x2050 pixels. Keep in mind that for the Girl with a Pearl Earring, we used a crop: we only captured the central part of the image, using 2000x2000 pixels for each tile. Also I used a 20% overlap in X and 20% overlap in Y. I will let you do the math!
In any case, I’m not sure how you end up with your calculation of 4x but please don’t compare our fully motorised XYZ high end system with a triple objective telecentric lens to a plastic USB microscope
2500 pixels for a horizontal FOV of 3mm is actually really not too far away from a 4x magnification for a conventional microscope lens on a regular camera sensor - for example on a camera with a 3,91 micron pixel sensor (like the Sony A6*00 cameras) the sensor is 23.5mm "long" with a resolution of 6000 pixels. So every mm has a resolution of approx 255 pixels, 3 mm have approx 766 pixels - and that's at a life-size reproduction (1x).
In order to get a FOV of 3mm projected onto 2500 pixels you need to magnify that area around 3,26x - with an additional pretty hefty overlap of 1750 pixels left and 1750 pixels right (=29% overlap on each side) without having to crop the image.
Though it would make more sense to either use a higher magnification with a higher effective resolution - or keep the magnification and effective resolution the same but use a larger FOV with a smaller overlap - which would result in fewer images necessary to cover the whole painting.
Having said that it would probably require a larger setup and it would be much more difficult to move the camera with all that additional weight etc. But that could be achieved with something like a Mitutoyo M PLAN APO HR 5X 0.21 or maybe even a Qioptiq Mag.x LD PLAN APO 5X 0.20 with a good tube lens.
There are a lot of ways to pet a cat.