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Rodenstock-Ysarex recalculated Tessar design/construction info? (R Knoppow ?)
Hello:
I bought a box of several apparently unused Rodenstock-Ysarex 127 mm f/4.7 front cells. There are 2 elements in it, the front being a meniscus (concave-front, concave rear, roughly 45-50 mm f.l.), and the rear element being double concave (I thought the 'front' of the rear element was planar but found about 0.025" height with a dial indicator. Does anyone (Rich Knoppow?) know what elements was in the rear portion of this lens, and which elements were the porportedly 'hot' glass? It's supposedly a recalculated Tessar and presumably still has 4 elements in 3 groups. I am trying to find an experimental use other than replacements for scratched Polaroid 110B's. I did unscrew the front cell from a Polaroid Tominon 127 mm f/4.7 and was able to focus it at (very) approximately the same distance as the Tominon - very unscientific test, handheld, projecting a light bulb onto a cinderblock. I was just trying to find SOMETHING it would focus with. Thanks Murray |
#2
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Rodenstock-Ysarex recalculated Tessar design/construction info? (R Knoppow ?)
"Murray" wrote in message m... Hello: I bought a box of several apparently unused Rodenstock-Ysarex 127 mm f/4.7 front cells. There are 2 elements in it, the front being a meniscus (concave-front, concave rear, roughly 45-50 mm f.l.), and the rear element being double concave (I thought the 'front' of the rear element was planar but found about 0.025" height with a dial indicator. Does anyone (Rich Knoppow?) know what elements was in the rear portion of this lens, and which elements were the porportedly 'hot' glass? It's supposedly a recalculated Tessar and presumably still has 4 elements in 3 groups. I am trying to find an experimental use other than replacements for scratched Polaroid 110B's. I did unscrew the front cell from a Polaroid Tominon 127 mm f/4.7 and was able to focus it at (very) approximately the same distance as the Tominon - very unscientific test, handheld, projecting a light bulb onto a cinderblock. I was just trying to find SOMETHING it would focus with. Thanks Murray I haven't been reading the Usenet groups regularly lately so pardon the delay. The Ysar and Ysarex are Tessar type lenses. I don't know the difference between the lenses sold under these two names other than the Yserex seems to be common on Polaroid cameras and oscilloscope cameras. A Tessar has a font element consisting of a nearly plano-convex lens in the front and a bi- concave in the rear. The combination has little power and is negative. The rear element is a bi- concave and bi-convex lens cemented. Sometimes the surface facing the stop is nearly plano. The rear has most of the power, the front has most of the corrections. If these cells have positive power, that is if they magnify or can project an image, the lens is NOT a Tessar but probably a double Gauss of some sort. There are two types of four-element air-spaced lenses found commonly. One is the Celor or Dialyte type. This has elements which are all bi-convex or bi-concave. The outer elements are bi-convex, the inner ones bi-concave. This is the generic type of the Apo Artar, Kodak f/7.7, 205mm Ektar or K.A., Goerz Dogmar, etc. The other is the double-Gauss type. In these all the elements are meniscus with the concave surfaces facing the stop. This is the generic type of the Kodak Wide Field Ektar and many other medium wide-angle lenses. Both have been used for general purpose lenses and for copy lenses. The Dialyte has rather narrow coverage, the double Gauss rather wide coverage. I think someone on this group identified the Tominon as a Dyalite not too long ago. I have no idea of which element(s) might be radioactive. In any case the radiation from most older Lanthanum glass elements is very low. The radioactive substance is Thorium. Thorium was added to the Lanthanum to modify its optical properties, usually in very small amounts. Some lenses have been made with significant amounts of Thorium glass, mostly special purpose military lenses. One needs to take care about some older aerial mapping lenses, but consumer type camera lenes are generally not hazardous. -- --- Richard Knoppow Los Angeles, CA, USA |
#3
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Rodenstock-Ysarex recalculated Tessar design/construction info? (R Knoppow ?)
Say, Richard, if an iris is offset from 'center' in a symmetrical
lens, does this achieve asymmetry, vignetting, or just alter coverage? Then, if, say a pair of symmetrical menisci are altered to two different focal lengths, presumably achieving asymmetry does the longer or shorter f.l. determine where the iris goes? I downloaded OSLO EDU...I need to figure out how to use it and do some experiments to start answering my too-many questions. Thanks Murray |
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Rodenstock-Ysarex recalculated Tessar design/construction info? (R Knoppow ?)
Making progress -
I intuitively figured out part of the math for 3 elements and Primitive Photography (Greene) confirmed what I was missing. I found a + lens that allowed me to focus an image combining it with the R-Y front cell. Now for a little re-calculating to see what working range I can get out of it. Thanks Murray |
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