View Full Version : Conway f/8 triple focus

Philippe Gauthier
17-Mar-2004, 14:26
I just bought a lens called "Conway F.8 Three Focus Rapid Rectilinear" - a very old brass lens with old style f/stops numbered 4 to 256 (I know the modern equivalent is f/8 to f/64). The Wollensak brass shutter boasts three focal lenghts, 12.5, 20 and 28 inches, but I don't know how to get beyond the basic 300+ mm configuration. So far I tried to remove the front element, but I ran out of bellow draws before I could focus on the building the other side of the street.

Does any one knows how to use this lens? Any other information would also be appreciated - I read about this Conway company, but know nothing about their lens line up. Serial number is #1221, in case anyone can date it that way (miracles do happen from time to time). My guess is that construction dates back from about 1905-1910.

Ernest Purdum
17-Mar-2004, 14:53
Essentially, lenses of this type are of the basic Rapid Rectilinear construction, one achromat, composed of two meniscus elements, at each end, but with a longer focal length cell at the front than that at the back. With only one cell in place, you have what used to be called a "landscape" lens, of the Grubb Aplanat type. You would need a very long bellows to use the lens to its full potential, since there is no telephoto effect. You were on the right track taking off the front cell, but you'd need approximately 20" (510mm) draw just to focus at infinity. To use the 28" cell, you'd take both off and put the front cell on the rear. Usually there are three sets of aperture markings. If there are not, however, you can work it out by measuring the diaphragm size and dividing that into the focal length. (This doesn't work with lenses having a cell in front of the diaphragm.)

Philippe Gauthier
17-Mar-2004, 15:30
Bizarre... The lens is mounted on a Seneca View, which provides me with a lot of bellows and about 30-32 inches of rail. It seems that I stretched it way beyond 20 inches after removing the front element without getting any focus. But I'll give it a second try.

I don't know much about Rapid rectilinear contruction and even less about a "Grubb Aplanat" (never heard of the later, actually!). Any bit of lore about this would be appeciated.

Dan Fromm
17-Mar-2004, 15:47
News from the Vade Mecum on the Grubb Aplanat: "T.Grubb designed and patented the Grubb Aplanat, a new better form of achromatic meniscus, even though it was near one component of the Ross-Collen lens (where Ross had envisaged its use separately as a meniscus), and Grubb was 'disappointed' when Dallmeyer was able to patent the RR as he stated he had used the design and that it was well known, the cells being like his aplanat."

Try removing the cells and using them to image something not too close on a wall. That will give a quick rough indication of their focal lengths and how much extension you'll need with each. Try the front cell facing both ways.



Philippe Gauthier
17-Mar-2004, 15:53
Hmmmm. Did a second experiment. Still no way to focus removing only the front element - at about 27-28 inches of bellows lenght, it seems to be nearing focus, but I would be needing more.

In a third experiment, I replaced he front element, then removed the rear one. I get a lot of magnification over the basic 300-odd mm configuration (the image is almost twice as big) but I need only 16 inches of bellows - no need to add the extension rail at infinity.

A fourth experiment without any element would turn my camera into a pinhole. ;-)

Philippe Gauthier
17-Mar-2004, 16:05
Dan: Both elements can only be fitted one way! And it makes me nervous when I hear stories about my lens being designed before Steiglitz ever shot a single frame, back when George Eastman was a creative young man... ;-)

In a fourth experiment, without the rear element, I needed about 21 inches of bellows to focus on something about 2 meters away. The width of the (vertical) coverage at this distance was about 60 cm (2 feet).

Well, at the very least, it seems that I've found a way to usefully tap the resources of a second focal lenght on this antique.

Ernest Purdum
17-Mar-2004, 19:52
Thomas Grubb was an Irish (hey, it's St. Patrick's Day) telescope maker. He designed his Aplanat in 1857. The name "Aplanat" was chosen to indicate low spherical aberration. It has two meniscus shaped elements, the positive one being closest to the diaphragm. The Rapid Rectilinear was developed apparently virtually simultaneously, by Dallmeyer in England and Steinheil in Germany, in 1866. Steinheil also used the name "Aplanat". There were very many variations on the basic design, including several other triple convertibles, and they were made for many years by just about everybody in the lens business. Until anastigmats became available in the first years of the twentieth century, they were the best general-purpose lenses available. They were called by many different names. Kingslake, in his "A History of the Photographic Lens" lists twenty-nine of them.

Philippe Gauthier
17-Mar-2004, 21:17
Fascinating piece of photographic lore, Ernest. Thank you very much. I really had no idea that the design went back to the wet plate days... and almost to Daguerre himself. It was obviously a very successful design to have lasted so long in a era where everything was moving so quickly in the emerging trade of photography.

Now, what can I expect from that piece of glass, compared to a modern lens? Low contrast and virtually no resistance to flare, I presume; but how does it behave at small apertures (it stops down to f/64). Lots of diffraction? Is there any serious color correction - after all, the panchromatic film days were far ahead - and is this purely designed for blue light?

The old age and small defects might actually be interesting to me. I'm shooting of era style pictures right now and my hope is that the lens will provide some authenticity to alt processes contact prints. But my fear is that it might ultimately be a bit too soft for the tastes of most modern viewers.

Mark Sampson
18-Mar-2004, 05:49
It seems that this lens would be suitable for re-creating the look of Eugene Atget... perhaps you need to find some printing-out paper and gold toner.

Ernest Purdum
18-Mar-2004, 08:04
I'll try to make some predictions as to the lens performance, but not all R.R. lenses behave the same, so you won't have the full story until you put it to work. Contrast - probably lower than you are used to. Flare - probably rarely any problem. Use a lens hood. Small apertures - you can stop down much further with a big lens like this than a small one. Use as small a setting as you need, but not smaller, and don't worry about it. Color correction? It is achromatic, two colors brought to the same focus, which was the case with the vast majority of lenses until very recently.

The R.R. wasn't intended to be a soft focus lens, and was actually fairly sharp, particularly when used at f16 or thereabouts, which was usually the case.

To get an idea of what to expect, you can look at pictures made in the 1880-90 period. Other than formal studio portraits, many of which were made with Petzval type lenses, the majority of those made by professional photographers were R.R. products. Later, most of the ubiquitous 3A Kodaks had R.R. lenses. The owners carefully followed all the instructions and provided us with more knowledge of the world at that time than ever before.