Lens Element size help needed

Hello all. I am asking for help from anybody who has a Rodenstock 300mm f5.6 Sironar-N in copal 3 shutter. I need to know the size of the Outside Diameter of the rear element. I just received a lens from a very reliable seller. It is a used lens sold with no front lens cap.

OK so I go do some research as to the size of the front element. I find a number of sites that list the fron element at 90mm. So off to KEH and order a replacement cap.

The problem lies with the size of the rear element. I find sites that state the rear element is 80mm. The element on the lens I have is only 70mm.

Does anybody else have the same lens, and could they tell me the size of their rear element. The S/N for my lens is 10933370.

Thanks for any help that people can give me.

I own an inexensive little digital caliper. You can get these from tool vendors online, as well as many local discount tool shops. With this tool, you can easily measure the size of any and all lenses you have and order lenscaps based on your measured size. Lens manufacturers often change things during the long lifespan of a lens.

You should not assume that your lens is mismatched until you try it out.

Dan how did you measure?

The sites you saw might have listed the rear filter size. If they listed the cap size it's measured the outside of the lens. But some caps fit inside.

http://www.butzi.net/rodenstock/apo-sironar-n/page2.htm

Is that the one you found online? That's the APO version of the lens. I don't know if they changed anything. If you ask on the large format forum I'm betting Bob Salomon will know the exact thing you need.

PhotoOne, thank you for your reply
I have a 210mm lens that has a front element with an Outside Diameter of 70mm. I took the lens cap off of that element and it went on the rear element of the 300mm. A quick and dirty way to prove to me that the rear element is not 80mm.

I have mounted the lens on a board and attached it to my camera. The ground glass displays an image. A very nice image. I have not yet shot any film yet. But I am concerned that a mismatched set of elements will not allow me the same movements as a properly matched set.

So I am asking if anybody else has a similar setup.

DanMcGuire said:

PhotoOne, thank you for your reply
I have a 210mm lens that has a front element with an Outside Diameter of 70mm. I took the lens cap off of that element and it went on the rear element of the 300mm. A quick and dirty way to prove to me that the rear element is not 80mm.

I have mounted the lens on a board and attached it to my camera. The ground glass displays an image. A very nice image. I have not yet shot any film yet. But I am concerned that a mismatched set of elements will not allow me the same movements as a properly matched set.

So I am asking if anybody else has a similar setup.

Click to expand...

Dear Dan,

If you get a sharp image, I'd suspect that reality (= your lens) is more believable than any web site. The likelihood of a mismatched rear element working at all well is slender.

Cheers,

Roger