[alfa75ts]

the results of my attempt is here

I think you need to do the test again.

You need a shallower DoF, less than 1" is good.

I would suggest, wide open (f4) @ desired focal length (300mm) distance would be about 12 feet.

Use a tripod (or other support), be accurate with your setup (centered on your target and 45° to the scale).

More lights, centre focus point, good exposure.

This will give a result which is easier to interpret.

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[SharkyCA]

I am going to run a new series of tests, but first I will try some shots at the settings currently in the camera (+5 from 0)