Barrelcactusaddict,
There is no disagreement between what Scarodactyl told you (correctly) and what holdinghistory has done in the example you provided. However, it appears that you’re getting tripped up by how magnification is achieved in different types of photography. The examples you cite from B&H and The-Digital-Picture are appropriate for telephoto lenses used alone with distant subjects, such as bird photography.
What holdinghistory is doing, and what Scarodactyl explained, is the use of a pair of lenses for macro or micro photography. Holdinghistory is, in fact, demonstrating a pair of lenses—the 200mm lens plus a 5x microscope objective attached in front of it. If you dig into the specifications for the microscope objective, you’ll find that its focal length is something close to 40mm. With paired lenses, the magnification on sensor equals the focal length of the rear lens divided by the focal length of the front lens: 200mm / 40mm = 5 X.
Note the mitutoyo 2x objective is a real underperformer, particularly in chromatic aberrations towards the corners even on aps-c. That may matter less in amber where things are more monochrome.
I don’t disagree with these observations, but do weigh them somewhat differently in my work. While it’s true that there are considerably better performers at 2x, and I have a few, I more often reach for the Mitutoyo 2x for its convenience. It is parfocal and parcentric with the other Mitutoyo objectives, which means I can use it without rearranging anything between 2x and 100x. Also, the particular type of chromatic aberration it exhibits (lateral, and largely limited to blue) is easy to correct in post. And as Scarodactyl said, it’s probable that very little blue light gets through amber.
--Chris S.
--edited typo