Washer, Waterhouse Stops

[Brassai]

I have some lenses from 1840s and 1850s, and have some questions. One of the lenses, a Derogy Petzval, came with washer stops. Another, an 1865 Voigtlander, has a slot for stops. An early anc. Darlot I have has a slot and a set of Waterhouse slots. These have all raised some questions in my mind. How did they decide on what diameter to make the holes? I'm assuming there was no real system in place at the time because there was no ISO rating, no shutter speeds, no uniformity between makers. I'm going to guess that they simply made the stops so one let in half (or twice) as much light as the next size? Or, was it pretty arbitrary?

Second question is when did an organized system of exposure come about? I've read there was a convention in Paris in 1900 that dealt with it, but I know there were at least three systems still going on at that time. I have equipment of that vintage such as a Kodak with stops numbered 1-2-3-4, a 1930s Elmar lens with stops such as f9, f18 (Continental System?), and the British (now standard?) system based on "1" and the square root of two. (e.g f2.8, f4, f5.6.....) on my 1906 Heliar in Compound. OTOH, early Weston meters had several scales in the 1930s and 1940s. How and when did our current system come about? Was it the invention of accurate light meters in the 1930s that really drove the standardization?


George B.

[goamules]

The early lens designers knew the "rapidity" of a lens was based on what they called "apertal ratio." But in the daguerreotype era there was little need to stop down a lens, the whole impetus for designers was making the fastest lenses they could. By the 1850s and wetplate collodion, they needed a way to slow down a fast lens (Petzvals). Yet, I would think the first lenses to use interior restrictions were landscape "view" lenses, which required that to make them sharp enough to use. I've not handled a Chevalier, but it's reputed to be not so sharp, and probably could have benefited from stops. The early pillbox lenses by Lerebours had washer stops, so the concept was well understood.

Notably, later manufactures like Dallmeyer always had a waterhouse slot in their lenses. So by the mid 1860s it was common practice, and Dallmeyer knew the rapidity was based on focal length divided by working aperture. Dallmeyer, Zeiss, and others all had their own system until the F-stop ratio (halving the light) was slowly settled on between the 1870s - 1890s, I believe.

[Brassai]

That would coincide with the availability of commercial dry plates (and film.) Before that the collodion would have been mixed by hand by each photographer, and I would expect there to be a lot of variability as to speed. With standardized plates/film, one of the three pieces of the exposure puzzle falls into place. The other one was the development of shutters, but I'm not sure the speeds on those started to be be standardized until the 1890s. I have an 1887 Prosch Duplex capable of three speeds, but they aren't marked on the lens. My 1890 B&L lens isn't either, but I've seen lenses from the late 1890s that were. This all makes me believe there was a Paris convention in 1900 to sort all of this out and move forward. Tonight I'll dig out my caliper and measure the two sets of Waterhouse slots I have, and calculate f-stops. I'm betting that each set was made for a specific lens, and that the stops merely start as the lens as the base exposure, then the stop with largest hole will cut the light in half, the next size cuts it in half again............ At least, that's my best guess.


George B.

[Dan Fromm]

Kent, you should change your screen name on apug too.

The modern system has been settled since a congress in 1900. I believe that some manufacturers, e.g., EKCo and E. Krauss, took some time to conform, also that in a few specialized areas -- the one that leaps to mind is high performance macro lenses made by microscope manufacturers -- manufacturers never did conform.

[goamules]

... I'm betting that each set was made for a specific lens, and that the stops merely start as the lens as the base exposure, then the stop with largest hole will cut the light in half, the next size cuts it in half again............ At least, that's my best guess.


George B.

Which is by definition the "F-stop" method. Others made stops that let in 1/3, or 1/4th the amount of light, or whatever they thought would be useful. Even if one manufacturer always followed the same scheme, the hole size in stops have to vary, based on the focal length of each lens. But they understood from WAY back the basic formula is Speed = Focal Length / Apparent Aperture.

[Peter Gomena]

I have an old rapid rectilinear lens, circa 1895, that came with a single waterhouse stop. I calculated the aperture without a stop as about f/8, and with the stop as approximately f/18-f/20. The stop itself is neatly drilled at 5/8 inch. If I had the rest of the stops in the original kit, would they have measured 3/4", 1/2", 3/8", etc. based on common drill bit sizes, or would the manufacturer have calculated stops more to the a scientific f/stop scale? Is my stop original to the lens? Hard to say in any case. I have a feeling it was used without the stop for portraits and with the stop for outdoors use or group portraits, or maybe indoors with flash powder (!). It's just one of those mysteries.