I just bought a Schneider-Kreuznach 'Symmar" lens. It reads "F5.6@150 and F12@26 5". F12 seems a bit extreme at 265. Does anyone out there have the nomenclature for this lens? or maybe personal experience?.....................Thanks, Chuck (BTW , we need a catagory for "4x5 cameras and lenses")
Chuck: This the the first series of Symars. Use the front and back elements together, it is a 150 mm lens, read the f stop scale which was a 5.6 in it. For a 265 mm lens, take the FRONT element off, and use the f stop scale which has f:12 as the largest aperture. As a 150 mm lens, the performance is quite decent even by current standards. I've got one and I use it on trips when my control of my luggage isn't ideal. It never lets me down in comparison with my APO Symar. I don't know what you mean by f:12 being extreme, but it works and you'll be able to focus it. Better results at the 265 configuration require stopping down a good deal anyway.
In the good old days, like the 50s and 60s we were always told to remove the back cell. This would leave the front cell to protect the delicate shutter blades and keep them free from dust and other foreign matter that might be around when the front group was removed.
of course the lens groups are symettrical so it worked back then.
Seems it doesn't work now though.
But using the rear group only still didn't result in spectacularly sharp results with a converted lens.
I believe, unlike the convertible Protars which were symmetrical designs, the convertible Symmars are not truly symmetrical. The symmetry would typically automatically correct some of the aberrations, fully at 1:1 and a good deal even at other distances. When a single cell is used alone, one loses the symmetry and thus some of the corrections, which is why the performance is not as good as the combined unit - stopping down helps reduce some of these aberrations. The single cell should always be used behind the stop, because the position of the stop helps to correct some aberrations. However, sometimes, when the cell is used behind the stop, it increases bellows draw considerably and so the cell is sometimes used in front of the stop to reduce bellows draw. The performance will be worse in this position but in some situations the shorter bellows draw may be more important. Stopping down does not help lateral chromatic aberration and so, when using a single cell, the use of a strong monochromatic filter will help performance by reducing the amount of chromatic aberration. Having said all this, it is quite surprising how good some of the convertible designs are. And the weight savings are considerable, a boon if you backpack. Cheers, DJ.
Well I can't find any ancient data sheets on the Symmar but I do have one on the Sironar from Aug. 1975. What it says about the convertible Sironar is:
" Another essential advantage of SIRONAR-type lenses is that their special optical design allows the front component alone to be used as a Ttelephoto lens". In this case, it is only necessary to unscrew the rear component."
This is the same advice we were given when using the Symmar in photo school in the early 60's as well.
The Rodenstock price list from 10/75 also repeats the above instruction for the Sironar.
Of course the later lenses N, S, Apo, etc. are different design and this was not recommended.
Interesting. I think that does make for a handier design on two counts. One, thats already been mentioned, is that the glass protects the shutter. Two, when the cell is used behind the stop, the principle point of the cell lies behind the lensboard, which means that the bellows extension is definitely longer than the marked focal length, an unwieldy proposition, especially with cameras having limited bellows extension. When the cell is used in front, it does act as a tele since the principle plane is out in front of the lens. I wonder how the design adjusted for the stop position, though it was probably do-able. But I'm fairly sure the Symmars and the Protars suggest using the cell behind the stop. In any case, with a little stopping down and use of a strong, monochromatic filter, results can be quite decent. Not quite upto a modern, prime lens but pretty damn decent. Cheers, DJ.
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