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Old Mitutoyo Comparator


Cast Iron
Apr 25, 2007
Melbourne Australia
Recently picked up a PJ250 Mitutoyo Optical Comparator for the right price, (Free).
Look very old, has imperial Micrometer heads.
It has a 12V 50w Halogen downlight for a globe, certainly not factory. Cleaned it all up, and surprise, a nice clear shadow of a piece. Works well i think.
Its missing the glass for the stage, and one over the light path in the base, im sure i can obtain round glass to rectify.

Came with 10, 20 and 50 Magnification lenses, a viewing window with crosshairs, one with several cross hairs, 2 glass rulers with imperial measurements.

Is there a preferred light source? LED? Are there viewing windows available for measuring internal and external Radi?
Any tips on its use are more than welcome!



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Oct 14, 2010
Oregon, USA
Are there viewing windows available for measuring internal and external Radi?
Those silver pins around the perimeter of the frosted glass are for attaching reticle overlays (typically on clear Mylar or something similar.) As long as you get a reticle with the right scale to match your comparator magnification, you can get all sorts of radii, thread forms, small diameters, etc.
If you mean can you order an OEM replacement from Mitutoyo, you'd have to ask them.

M.B. Naegle

Feb 7, 2011
Conroe, TX USA
I've no experience with Mitutoyo, but I can tell you on our Jones and Lambson comparator, any light source does not work. Ours was an old Mercury Arc system with obsolete bulbs. I tried using a very bright LED array and it produced a dim projection that was further washed out by light hitting the outside surface of the screen from the projection source. Tungsten Halogen lamps are one of the newer technologies that work. There are companies that make plug-n-play retrofit kits, but for their cost IMO it wouldn't be hard to DIY it (though that's still on my to-do list).

How the unit focuses the light likely plays into things, but It's one of those games where you have to balance the time/finances of reinventing the wheel vs. getting something that works. Optical comparators are somewhat obsolete being replaced by digital camera technologies, but if it works why replace it?


Nov 22, 2015
San Francisco
IIRC changing the geometry of the light source will mess up collimation.
I've never done this myself, but I'd expect fuzzy edges as a result. An easy way to test is to measure a few gage pins and see if you get clear and correct results.
I haven't been inside that model, but I'm used to seeing first surface mirrors inside them. Care should be taken with cleaning or even touching those.