Rodenstock 120mm lens, Anyone familiar with this one?

[LanceO]

Hi All,

I recently went out on a limb and bought a Rodenstock Sironar-N 120mm f5.6 lens in a Copal 1 shutter without knowing much about the optics of this little puppy. It was a great price for a Rodenstock and a focal length I've been wanting to add to my collection, so I figured "what the hey!". Can anyone enlighten me about what I've just acquired?

sincerely yours, Lance

[Dan Fromm]

120 mm? Are you sure?

[Oren Grad]

I have one. It's an ordinary modern (early-'80s, I think) plasmat. A perfectly fine lens, like the rest of the Sironar-N line. It's unusual in two respects - first, Rodenstock didn't make that many of them before they discontinued that focal length. And second, very unusually for a lens of that general design and focal length, it comes in a #1 shutter rather than a #0. Nobody seems to know why Rodenstock did that.

Although it's uncommon and comes in an unusual shutter size for its type and FL, it's not especially valuable money-wise. But it's a good lens optically. Use it and enjoy!

[LanceO]

Thanks Oren, that helps a lot to know what type of lens design it is. I did a google search and learned a lot about plasmat lenses that I didn't know. I need to find a book(s) on large format lens designs. Can you recommend any?

[Bob Salomon]

You apparently have not searched the forum though.

This answer about the lens was posted by me in April of this year. A search of the forum with "120mm Sironar" will bing up the entire thread.

"Sorry, we have nothing that would stste why. But it would have to be for the same reason why a 90mm 4.5 Grandagon is also in a 1 shutter. Physical size of the threads on the lens groups. Otherwise they would have saved money and gone with a 0.

The only tech info I have is a flyer from 3/88 that shows the 120 Sironar-N being only in Copal, Compur and Prontor Professional 1 shutters and its having an image circle of 175mm. It was quite a bit larger then the 100 and 135mm Sironar lenses. They had a 40.5mm front filter thread while the 120 had a 52mm filter thread.. In fact it was also larger in diameter then the 150mm and only the 180mm and longer had a larger filter size. Also it had a 51mm diameter rear mount. That was the same size as the 180mm Sironar-N as well. The 150mm had a 42mm rear mount diameter. Lastly, the 120mm lens was 59mm long. A 180mm Sironar N was 57mm long. So don't look just at the focal length and assume it should be in a 0 shutter. This was quite a big lens for its focal length. Not as big as the 115mm Grandagon 6.8 but that lens was also in a 1 shutter."

[Oren Grad]

The only tech info I have is a flyer from 3/88 that shows the 120 Sironar-N being only in Copal, Compur and Prontor Professional 1 shutters and its having an image circle of 175mm. It was quite a bit larger then the 100 and 135mm Sironar lenses.... etc.

Sure, the cells were larger. The question is *why* they designed the cells for that particular FL in the standard plasmat series to be so large, when for every other focal length in the series all the dimensions scale more or less as you'd expect. The cells of a 90mm f/4.5 that covers 105 degrees need to be big, the cells of a 120mm f/5.6 that covers 70 or 72 degrees don't.

[Oren Grad]

Thanks Oren, that helps a lot to know what type of lens design it is. I did a google search and learned a lot about plasmat lenses that I didn't know. I need to find a book(s) on large format lens designs. Can you recommend any?

Lance, I'll have to defer to others to recommend a book on lens designs. For practical purposes, what matters is that plasmats are designed as normal lenses for their respective intended formats, with moderately wide fields and adequate room for movement at focal lengths that are at or near the diagonals for the recommended formats. Late-model plasmats from the major manufacturers (Sironar, Symmar, Nikkor W, Fujinon W) tend to be very competent lenses without major vices. Beyond that it's hard to generalize, as within the broad class of plasmat and modified-plasmat designs there is plenty of variation across manufacturers and product lines in details of coverage angle, optical correction and subtleties of rendering.

[LanceO]

I've kind of answered my own question, in my internet surfing I ran across a reference to a book titled "A History of the Photographic Lens" by Rudolf Kingslake. Amazon has it for $62.92, it appears to be pretty comprehensive. I think I'll look around some more and see if I can find it cheaper (I'm a true-blue cheapskate) :D

[Oren Grad]

I've kind of answered my own question, in my internet surfing I ran across a reference to a book titled "A History of the Photographic Lens" by Rudolf Kingslake. Amazon has it for $62.92, it appears to be pretty comprehensive. I think I'll look around some more and see if I can find it cheaper (I'm a true-blue cheapskate) :D

Do search the archives here if you haven't already done so - there's been some discussion here about books on lens design, it's just not a topic I stay on top of. If you need it you can post a query specifically asking for information on books - not everybody here can read every thread, and the folks who know enough to help you won't necessarily find your book question buried in this thread.