5x7 B&L lens -- retainer ring size?

<p>Hi all,</p>

<p>I've come into possession of a B&L 5x7 Tessar, Series 1c, Pat Feb 24, 1903, S/N 3017078, purportedly under license from CZ.</p>

<p>I'm trying to figure out the retaining ring size. The flange thread OD measures 57mm (2.25"). The thread pitch appears to be pretty close to 1mm (or 24 tpi?).</p>

<p>So would this be a metric or imperial thread? And is there anyone who would sell a handy dandy retainer ring, so that I don't have to fabricate one?</p>

<p>Thanks! :-)<br>

Sarah</p>

<p>Oh, and I'm thinking something like this would work. Thoughts?</p>

<p>http://www.ebay.com/itm/72mm-57mm-Step-Down-Ring-Filter-Adapter-/390705042953?pt=US_Lens_Adapters_Mounts_Tubes&hash=item5af7d5d609</p>

<p> </p>

<p>You might wish to try Large Format Forum, where guys normally have a lot of retaining rings of different sizes.</p>

<p>Of course! I forgot about the large format forum. I'm sure they'd have the answer. Thanks!</p>

 

<p>Sarah - I looked at my B&L Optical Co. 5X7 1c, serial number 3163757. The outer diameter of the threads on the lens barrel measure 2 1/4" or maybe slightly less than that. The thread pitch looks to be 24 tpi, although my thread pitch gauge goes 22,24,26 so I suppose it could be 23 or 25 tpi. There are only about three threads on the barrel to gauge, so it makes it a bit more difficult to be accurate. I checked with a metric pitch gauge and it looks close to 1.0 mm pitch, but I'm reasonably sure B&L in the era these lenses were made probably used US measurement not metric. Zeiss would have granted B&L license to use the Tessar optical formula and name, but the lens parts would have been made in Rochester NY on American inch standard lathes. That is my guess anyway.</p>

<p>I don't know of a source of off the shelf flanges for older lenses. There are places like S K Grimes who can machine one, but it will be expensive. It would probably be cheaper to buy another Tessar with a flange. There are a number of lens boards on eBay with unknown size flanges. With a lot of search and emailing eBay sellers you might find the correct flange. It should at least be a somewhat common flange since a 5X7 Tessar was a popular lens. A Wanted ad on the LF forums might work for you too. </p>

<p>There are all sorts of hacks to mount a lens to a board without a flange. If it is a wooden board, bore the hole in the wood slightly undersize and thread the lens into the wood. Glue the lens in with a bead of silicon sealer, which can be cleaned off if the lens ever needs to be remounted. A hose clamp around the rear of the lens barrel (hopefully with rubber between) to keep the lens from falling out of the hole in the board. Any of these will probably work, but won't be as secure as the proper flange so will need a bit more thought and care in use. </p>

<p>Len</p>

<p>Len, thanks! I guess I should have been more specific in my question, but you apparently read through the lines successfully. Yes, what is/was throwing me was the American manufacturer vs. licensure from a German company and whether that would mean metric or imperial. But your thoughts about the licensure being for just the optical formula makes sense. So it would appear I'm looking at a 2.25" x 24'ish thread.</p>

<p>I did post to the LF forum and explained there that I can lathe a part, but that my lathe is currently out of commission and located in another town, without power. So it will be a while until I can cut the threads I need. I've used the "screw the lens into the undersized hole" trick before, but what I'm wanting to do, for now, is to adapt this lens to a cheap set of Canon EOS extension tubes. (For something like $10, if I recall correctly, you get quite a few threaded tubes and both a male and female bayonette flange). Then I can mount the lens to an EOS bellows. I'd use the same extension tube system to mount up and play with other odd lenses. But Ideally, I'd be able to use the same threaded ring as a retainer ring for later mounting the lens in a lens board.</p>

<p>... or such are the demented thoughts of someone who is stuck inside during bitter cold weather.</p>

<p> </p>