Well yes, in essence.
We (that is my daughter with me sitting back and watching) did a fair amount of experiments with the QV 2.5x equivalent. I know it is not exactly the same but our results did seem to echo the Mitutoyo 5x. This was with the full frame Sony a900 which I think is more difficult to satisfy with ad-hoc tube lenses than APS-c.
135mm vignettes at least a little with any tube lens tried and I recon it is about low as one can go. We tried about 6 135mm primes with the best being the CZJ 135/3.5. It vignetted but I would consider it a good choice for APS-c.
Our best result was a Componon-s 135/5.6 enlarger lens with only the slightest darkening but it could do nothing about the generally mushy corners.
I think the quality area was a circle of about 22mm so for APS-c it would be about right. I doubt you will do better than enlarger lenses at 135mm but I have a sneaking suspicion that a cheap 4 element enlarger lens might be slightly sharper at f/12 with only the center of its designed field of view in use. They have essentially the same design as the CZJ.
For FF I plan to go up to about f/16 with a 180mm lens. My observations so far is that short lenses do better than long ones so I have ordered this one
http://www.surplusshed.com/pages/item/l14015.html . It is so small it should mount inside the mitutoyo!
Anyway we have more or less abandoned the mitutoyo for now. The Schnieder D-Componon 40/3.5 offers a lot more promise. The corners hold up a lot better.
Not that I am all that surprised. I have been checking results at
http://coinimaging.com and discovered an interesting thing. A lot of non-microscope lenses when mounted reversed on their own were found wanting because they offered poor sharpness at the magnifications that their apertures justified. However they all seem to offer close to diffraction limited resolution when stopped down to sharpest (often f/4.7) and the magnification was sufficiently raised. If a tube lens could be found that maintained that resolution then they would all be winners.
My guess is that, with a tube lens, for 0.1 NA and under there are a lot of 50mm lenses that will excel while there is a fair supply of 0.14 NA f/3.5 microfilm lenses that will challenge. I doubt that the 10x 0.28 NA mitutoyo has a lot to worry about though.
Anyway, with the D-Claron having a quality area that almost covers at 2.25x and f/8 I recon I have a real problem choosing the right tube lens. I am stocking up with enlarger lenses between 50-135mm and 50mm camera lenses. When my daughter comes back from university in the summer we are going to play.