Rodenstock Sironar-N lens mystery

[Oren Grad]

I have in hand a lens that is very strange indeed.

It is labeled Rodenstock 100mm Sironar-N MC. This labeling is clear and crisp, and shows no sign of having been tampered with. Serial number is in the range 1029xxxx. But the front and rear mount diameters match those specified for the 150mm Apo-Sironar-N. Compared side-by-side with a late-production 150mm Caltar II-N from the Apo-Sironar-N era, there are some cosmetic differences in the cells but overall cell dimensions and front/rear spacing look similar; the front and rear caps, respectively, swap between the lenses with exact fit.

Also for comparison, I have both 100mm Sironar-N MC and 100mm Apo-Sironar-N lenses, and the front and rear cells for both of those are substantially smaller, as per Rodenstock specification.

When I compare the "100" and the Caltar-labeled 150 on camera, focusing on the ground glass, the "100" appears to have an actual focal length slightly longer than that of the Caltar-labeled 150.

The obvious question is whether there's a rear cell mismatch here, but given the cell dimensions and strange labeling of the front cell, it's not obvious what it could be. A cross-brand mismatch, perhaps, as at least part of the story? But FWIW, none of the rear cells in the Apo-Symmar line matches the dimensions of the cells here.

Recall that this was the era when Rodenstock offered the 120mm Sironar-N in two different mounts (0 and 1 shutters) over a very short overall product life, so maybe there was some other tinkering going on at the same time.

Any ideas?

[consummate_fritterer]

Perhaps it's a 'factory second' sold at discount? Or maybe at least one mislabeled example left the factory by accident or via theft?

[Dan Fromm]

Um, Oren, which shutter is y'r mysterious 100 Sironar-N is? Should be a #0. What is the outer diameter of the front cell? Should be 42 mm. What is the outer diameter of the rear cell? Should be 31.5 mm. All this per Rodenstock Apo-Sironar N documentation, which may not be right for the pre-Apo Sironar-N.

The 150 is also in a #0 so the two lenses should have the same cell spacing. 20 mm flange of front cell to flange of rear cell. But the 150's front cell's o/d is 51 mm and the rear's is 42 mm.

[Bob Salomon]

Perhaps it's a 'factory second' sold at discount? Or maybe at least one mislabeled example left the factory by accident or via theft?

Rodenstock did not and does not sell factory "seconds". They might take a lens that does not meet spec and cut it in half and make a display lens to show the construction. Otherwise, if not useable as a photo prop or a display prop it would be destroyed.

[Oren Grad]

Dan, as stated in my original post, the "100" is in a Copal 0, and the front and rear cell mount (outer) diameters match the specification for the 150.

More in a little bit, have some pictures to process...

[Oren Grad]

Left to right: 100mm Sironar-N MC, "100mm" mystery Sironar-N MC, 150mm Caltar II-N (Apo-Sironar-N), plus a closer view of the two larger lenses. As you can see, the 150 Caltar cell-shutter-cell "stack" is actually a little bit taller than the mystery "100" stack.

167747 167748

EDIT: And on the off chance that the information might provide some dating clues that matter, the S/N range of the genuine 100 is 1061xxxx while that of the mystery "100" lens, once more, is 1029xxxx. The Copal 0 in which the genuine 100 is mounted is engraved 185xxx on the rear bearing surface and is stamped 86-10, while the Copal 0 in which the mystery "100" lens is mounted is engraved 129xxx without any stamping.

Finally, a careful measurement shows that I was wrong in my impression that the shutter of the mystery lens is thicker. All three shutters are the same in that respect. I'll delete that from the original post to avoid confusion.

[Dan Fromm]

Smells like an engraving error, but are the front lenses the same diameter?

Have you checked (crudely) focal length of the mystery 100 and the for sure 150?

[Oren Grad]

Yes, as stated in the original post, the mystery lens evidently has a focal length longer than that of the 150 Caltar II-N.

EDIT: I have the lenses in front of me again; the front-most glass element of the mystery "100" appears to have a slightly smaller diameter than the front-most glass element of the 150 Caltar II-N. Ditto for the respective rear-most glass elements.

[Dan Fromm]

Perhaps Bob Salomon will look in and put us out of our misery.

[Oren Grad]

...and put us out of our misery.

< curmudgeonly :) >

[MAubrey]

< curmudgeonly :) >

That Rodenstock quality seal is dripping with irony!

[consummate_fritterer]

Perhaps Bob Salomon will look in and put us out of our misery.

He already chimed in. He seems to be a good guy but I'm still miserable.

[Bob Salomon]

Perhaps Bob Salomon will look in and put us out of our misery.

Rodenstock had changed the construction of lenses. If you look for the early specs on the Apo Rodagon lenses and the later specs you will find that they redesigned one of them and made it a larger diameter front diameter.

[Mark Sampson]

Well, dang. Why not try taking pictures with the 150 and the mystery lens and see if you can tell any differences? I remember long ago, looking for old Volvo parts, and sometimes you had to know if your car was 'early' or 'late' 1967 production. They drove essentially the same, though...

[Oren Grad]

Bob, do you by any chance have in your files a spec sheet for the original plain Sironar (pre-N) series? (Sure, the answer is probably "no".)

Look at the groove around the front cell of the mystery "100" - I'm wondering whether that front cell may be a very early version of the 100 N that was actually transitional from the plain 100mm Sironar. And the idea that the rear cell could be a mismatch reminds me that the plain Sironar series was considered convertible, increasing the odds that someone would be messing with the rear cell.

[Jody_S]

Simplest explanation is that someone has put the wrong rear element on it, or combined 2 damaged lenses to make one that looks ok enough to sell.

[Bob Salomon]

Bob, do you by any chance have in your files a spec sheet for the original plain Sironar (pre-N) series? (Sure, the answer is probably "no".)

Look at the groove around the front cell of the mystery "100" - I'm wondering whether that front cell may be a very early version of the 100 N that was actually transitional from the plain 100mm Sironar. And the idea that the rear cell could be a mismatch reminds me that the plain Sironar series was considered convertible, increasing the odds that someone would be messing with the rear cell.

No, I don't. And I never saw a transitional lens come out of the factory.

[Oren Grad]

Found another one on eBay with an even earlier S/N, 1011xxxx, also marked Sironar-N MC, with the same disproportionately large front cell but a compact rear cell. It's in a silver rim Copal/Wista 0.

So it looks like there was an early version of the 100mm Sironar-N which physically resembles the older convertible Sironar, which also had the disproportionately large front cell. No way to say at this point whether the optical design is the old Sironar design carried over but with multicoating added, the new design that appeared in the more compact version of the 100 N later on, or something different from either.

So my current working hypothesis is that I've stumbled upon an early version of the 100 N that I previously didn't know about, but that my sample has a mismatched rear cell.

[MAubrey]

Found another one on eBay with an even earlier S/N, 1011xxxx, also marked Sironar-N MC, with the same disproportionately large front cell but a compact rear cell. It's in a silver rim Copal/Wista 0.

So it looks like there was an early version of the 100mm Sironar-N which physically resembles the older convertible Sironar, which also had the disproportionately large front cell. No way to say at this point whether the optical design is the old Sironar design carried over but with multicoating added, the new design that appeared in the more compact version of the 100 N later on, or something different from either.

So my current working hypothesis is that I've stumbled upon an early version of the 100 N that I previously didn't know about, but that my sample has a mismatched rear cell.

Fascinating. Thanks for letting us watch the mystery unfold!