Protar VII Plastigmat Dagor How they differ from each other.

[jimgalli]

Thought the folks here might enjoy this little sketch of the 3 cross sections seen together. I've been curious for a long time about how the Plastigmat was actually different from it's more costly brother the Protar. I had concluded that B&L likely changed the Protar just enough to not get sued for patent license infringement and changed the name to Plastigmat calling it their own design. It turns out the Plastigmat is much closer to the Dagor than the Protar! The 4rth glass in the P-mat seems to have corrected it better to be used as a single and Bausch & Lomb always provided 2 aperture scales calling it a symmetrical convertible. A double convertible but never a triple like the Protar that could have different lengths at each end. I've shot with a single element of a Dagor before but it really isn't good enough to be thought of as a viable convertible lens. In the drawing it's easy to see the Plastigmat is simply a Dagor with the entry end glass divided into 2 elements.

[Ole]

It asks me for a password - what have you done???

1: B&L didn't make the Protar - Zeiss did. B&L was one of many license producers.

2: Zeiss used the name "Protar" for all their cemented anastigmats after the original name "Anastigmat" was used by everyone else, too.

3: There are at least 8 different types of "Protar", with different design and properties. Some of them are very close to the Dagor (or Doppel-Anastigmat Goerz to call it by its original name). Others are very different.

4: Using four elements in a cell is a very different matter from using three, the calculations (by log tables and pen and paper, remember) are so much more complex that calling it "simply a Dagor with the entry end glass divided into 2 elements" is much too simple. If the two glasses had been equal it might have been correct, but as they are not it's a completely different lens.

[jimgalli]

Ole, look at the title. I'm talking about Protar VII irregardless of who the mfg was. B&L owned the Plastigmat so they are the only producer of that lens. The picture is fixed. Calculations aside it's easy to "see" the similarities.

[Ole]

But... That means a reduced version of the Protar VII (center element not split) was the basis for all "Reverse Dagor" lenses - like the Angulon?

Around that time there was a staggering number of slightly different lenses with slightly different designs, with anything from 2 to 6 elements per cell. Tracing the "derivations" is fun, but doubtful

[jimgalli]

Fair enough I suppose. I just look at the 3 profiles and think "I'll bet these guys........"

[John Z.]

Quick question for Jim, and Ole too; I have a 19 inch Dagor lens, and just found on doing some research I can use as a single element and essentially have a 33 inch Dagor. It is know that Ansel used this technique on a few of his photos; what problems have you seen? Does it matter if you use the front or the rear element? I have read that using a smaller aperture helps to avoid abberation.

Second question for Ole, the Protar expert; I have a LeCLerc lens that was sold to me as a early Protar variety; any way to know which type of Protar this was? I do like the lens a lot, even though it is pre-1900's. Thanks.

[Ole]

Using the rear half of the Dagor gives a 33" half-Dagor (sorry, but it's exact!). Max aperture will be about f:18, and it should be stopped down at least to f:32 for use. Chromatic and spherical aberration is high, and astigmatism visible, but stopping down helps.

Using the rear element (or the front element behind the stop) gives flatter field and less distortion, but needs a lot more bellows draw. Using the front element needs less bellows, but is optically worse. The rule is always to place a single cell behind the stop.

Protar:

Series III f:7.2 rear doublet
Series IV f:12.5 rear doublet
Series V f:18 rear doublet
Series I f:4.5 rear triplet
Series II f:6.3 rear triplet
Series IIIa f:9 rear doublet
Series IIa f:8 rear triplet

The best way is to count reflections and check max aperture...

However LeClerc is not listed by Kingslake as one of the licensed Protar-makers, so it might be another anastigmat formula - of which there were lots.

[jacobus]

Jim,
this Plastigmat design looks rather similiar to the designs of three other quadruplets: Reichert's COMBINAR ( an Austrian lens); Suter's Anastigmat ( made in Switzerland); and especially to the OCTANAR, made by O.Simon, Dresden. The last lens was patented 1902 by DRP 168 977.
If you have the radii, thicknesses and refractive indices of the Plastigmat I could send you the specs of those three designs for closer comparison.
Uli

[jimgalli]

Jim,
this Plastigmat design looks rather similiar to the designs of three other quadruplets: Reichert's COMBINAR ( an Austrian lens); Suter's Anastigmat ( made in Switzerland); and especially to the OCTANAR, made by O.Simon, Dresden. The last lens was patented 1902 by DRP 168 977.
If you have the radii, thicknesses and refractive indices of the Plastigmat I could send you the specs of those three designs for closer comparison.
Uli

No, not necessary. I was just musing out loud but your point strengthens Ole's argument that similarities don't really mean much.

[df cardwell]

The Plastigmat was B&L's economy lens, an inexpensive alternative to the Protar VII, which it manufactured in the USA under license from Zeiss. The Plastigmat was slower, and the spacing allowed the use of B&L's own shutters ( at the time, B&L made a lot of shutters ! ). It was intended for hobbyist cameras, not for pros. In other words, the B&L house wine was the Plastigmat. A good lens, not great. The Protar VII, by any measure is, was, and will be a great lens.

I have Krauss and Ross Protars ( Combinable ! ) as well as CZ: all are wonderful lenses.

There have been some fine reworkings of the 'cemented quadruplet' system. It was originated by Rudolph to accomplish in a single cell was in effect a complete Rapid Rectilinear set. The Meyer was well done, as was the Wollensak. There have been horrors as well. Both the Goerz Satz Anastigmat and Turner Reich Anastigmat used 5 elements rather than 4, and most of them were badly centered. The Turner Reich is common in the USA: many were made under government contract and were generally adequate for contact printing but uncentered and useless for enlarging. It is relatively easy to reassemble them in in an optical shop and make them sparkling performers... but there are only a few shops who still do this work ( I know of 2 ).

I always thought the Dagors do a good job with their single cell. Not quite as good as the Protar, but good enough for most purposes. I've never had regrets using a Dagor or Angulon as a convertible lens to make a shot, but they aren't fully corrected. If you are trying to get a lot of detail sharply drawn, bring out the #12 filter, or an orange filter.

Oh yes. It is essential that the single cell be used BEHIND the aperture.


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