A Comparison Densitometer

 

densitometer

 

We'll be honest: it took us a while to work out what it was, not least because it is no longer in full working order. The box is the transmission densitometer itself, and the thing in front is a graduated wedge of different densities, from all but clear (on the left here) to all but opaque. When it's not in use, the wedge is stored in the slot with the little brass swivel tab, and when it is in use, it goes into the slot just above the hinge, on the right in this picture. The big brass clip on top is to hold a processed plate on the black velvet surface: you position the bit you want to measure over the hole, which is just about visible here above the tip of the big clip.

Under good, diffuse light, you now slide the wedge into the slot and look through the round hole beside the storage slot. Inside the box there's a mirror or prism arrangement (we haven't actually had it apart) with a split field. One side shows the bit of the negative above the hole, and the other shows the bit of the wedge under the round hole above the wedge-slot, next to the clip. Slide the wedge left or right until the densities match, and lo and behold, you can read the density from the scale on the paper label alongside the wedge.

Sanger-Shepherd & Co. was founded by E. Sanger-Shepherd in about 1900; became a limited company in 1910; and ceased trading in 1927. As this is marked as Sanger-Shepherd & Co.Ltd. it must date from between 1910 and 1927. Unfortunately, however, it doesn't work any more. You might think there was very little to go wrong, but the sad truth is that after the best part of a century, the step-wedge is cracked and degraded and the split-field viewer is dim and spotty. But it's a fascinating piece of photographic history. If you're interested in more modern densitometers, go to the piece about our Heiland.

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© 2010 Roger W. Hicks