My best one you can't buy anymore, and not many were made to begin with. It was a ZBE easel densitometer, and quite expensive. The problem with all these devices is that they can't correct for cosine errors - that is, angle of light incidence off axis. You have to take measurements directly below the lens. Once there is a diffusing sphere it requires a different kind of design, though I have both. I use these for color printing sometimes. They are redundant for ordinary black and white work, where simple test strips will do. For example, miscalculating the density of a big Cibachrome print could cost you a hundred bucks a pop. All the masks and calibrations had to be spot on, and even then a 50% batting average would be a very good day. With RA4 chromogenic paper, a few test strips and a disposable work
print aren't terribly expensive, and meters don't read thru those orange masks ideally anyway. For diagnostic testing - plotting film curves,
generating critical color separation negs and mask, that kind of nitpicky stuff, a good easel densitometer is worth its weight in gold. But
don't confuse these instruments with traditional color analyzers.