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View Full Version : What is a "Plasmat"



Bruce McCrory
20-Jan-2004, 21:51
This term is quite prevalent on the forum but I have found nothing to identify what a plasmat is. It sounds generic, like "coats". I even checked my copy of View Camera Techniques, 7th; College dictionary, and, Google. I think I ran across filters with same identity.

Since I'm sure the answer for the above term is something simple, do I need to open a new subject for "convertible" lenses?

My understanding is these are switchable elements of a lens group. Is there a way to recognize one besides being told? Again, Stroebel has nothing much on them. They sound like a good option for a beginner. "Two-fer-one" mentality.

Thanks, Bruce

Colin Carron
21-Jan-2004, 01:30
Bruce, As you say Plasmat is now used generically for a more-or-less symmetrical 6 element design introduced (I think) by Hugo Meyer in the 1920's. It had a larger image circle than the previous top of the line 4 element Tessar and better sharpness away from the centre of the image. It came into its own after WW2 when lens coating made the 6 element Plasmat a more viable proposition. Before that the Tessar was cheaper to make and had better contrast. Today most LF 'standard' lenses are Plasmat type e.g. Schneider Symmar, Rodenstock Sironar etc.

The early Schneider Symmars allowed the front element to be removed turning the 6 element Plasmat into a non-symmetrical 3 element lens with sufficient corrections to be used as a longer focal length lens so the 150mm Symmar becomes a 265mm. The quality of the triplet is OK for non-critical situations but it has a max aperture of f12 making it quite dim on the ground glass. The later Symmar-S and Apo-Symmar are not convertible. You can tell the convertible ones by the name (Just Symmar not Symmar-S or Apo-Symmar) and the second green aperture scale for the converted configuration.

The convertible Symmars are single coated as opposed to multicoated for the later types. This does not make a huge difference provided you shade the lens. They are a good economical way of getting a high quality LF lens because they are cheaper than the more modern versions and mostly still work fine. The convertible thing is probably not used much by most Symmar owners and I would concentrate on using a convertible Symmar in its primary focal length.

Dan Fromm
21-Jan-2004, 04:12
Plasmat = 6 element more-or-less symmetrical lens, elements arranged 2 + 1 + i + 1 + 2. 2 = cemented pair of elements, i = iris. LF Plasmats typically have max. aperture f/5.6 or smaller. Usenetters frequently assert that Plasmats aren't much good wide open, but I think this depends on the lens.

Opic/Planar = 6 element more-or-less symmetrical lens, elements arranged 1 + 2 + i + 2 + 1. Can be very fast, e.g., the f/1.9 Dallmeyer Super Six. The design isn't much used for LF lenses. Don't hit me, I know there are 5 element Planars too.

Arne Croell
21-Jan-2004, 06:20
Historically, the name Plasmat goes back to the Company Hugo Meyer, as mentioned above. It was derived from the Goerz Dagor, by splitting off the two inner elements from the cemented triplets of the Dagor. The designer was Paul Rudolph, the former Zeiss designer of Planar, Tessar and Protar fame (plus a few others). He had retired from Zeiss, but after World War I he had to go back to work because he lost most of his money in the finanacial turmoil after the war. He didn't go back to Zeiss but decided to work for Meyer, and the Plasmat was his main contribution there. Meyer actually had a similar design named "Euryplan", that came to them by the merger with the optics company Schultze and Billerbeck. However, Plasmat was the name that stuck with this design. Meyer made a convertible Plasmat ("Satz-Plasmat"), but also other versions not intended to be convertible like the Makro-Plasmat and the Kino-Plasmat. Like the Planar, it benefitted from the invention of coatings after WWII and became the standard design for moderate wide-angle LF optics. Meyer itself did actually not continue the design after the war, but it was picked up by other companies. Occasionally, another element is added like in the Apo-Sironar W to enhance coverage; despite having more than 6 elements, its still a Plasmat type.

Peter Collins
21-Jan-2004, 06:26
Thank you, you superbly knowledgeable forum buddies!!! I had no hope of learning this arcane and interesting stuff on my own, and here it is, clear as can be! Again, many thanks for educating me.

Bruce McCrory
22-Jan-2004, 15:05
Thanks for clearing up my confusion regarding Plasmat lenses. After a month of digging, LF is beginning to have an appearance of order. A long way to go, still.

Julio Fernandez
22-Jan-2004, 20:44
Arne: great posting, thanks! (and I thought I knew the answer, ha!).

Randy Cole
7-Nov-2005, 11:04
I have recently acquired a very clean Meyer & Co. Gorlitz Euryplan Satz Doppel Anastigmat 13.5cm triple convertible lens mounted in a dial set compur. The other two focal lengths are 26.2cm (front group), and 20.9cm (rear group). The serial number is 409306.

I am wondering if this is a plasmat lens, or a tessar type, as it appears to have only 4 elements - the lens groupings both unscrew to reveal a thin inner lens, and a thicker outer lens. I would like to ask, does anyone has an idea of coverage, sharpness and $ value for this nice old item? Any feedback will be appreciated.

Randy

Ole Tjugen
7-Nov-2005, 12:42
Convertibles are never Tessar type - or rather: Tessar constructions are never convertible.

The Euryplan is likely to be a Dialyte, 1-1-i-1-1 type. Just like the Rodenstock Eurynar of similar age. According to one of my sources, the Eurynar (I remember this since I have one) was one of the sharpest lenses available, easily outperforming the more famous Protar and Dagor lenses. However the 8 glass/air surfaces gave low contrast and lots of flare...