D. L. Jochum , Jul 14, 2006; 09:19 a.m.
I'm selling this lens for a friend. Is it a 50mm 35mm? what does the 1:2.5 and
f=18cm mean? I have it listed on Ebay and wonder if it's listed and discribed
correctly. Here is the Ebay listing#290007702079 there are pictures to help ID
the lens. The lens belonged to my friends brother who passed away. He was a
freelace photographer in the 60s & 70s. I got some info for Neil Parker and
Michael R. Freeman yesterday on this site that I used to make up the listing.
But I must not have used the info correctly. Thanks for anyones help in
advance, Dennis
Adam Maas , Jul 14, 2006; 10:09 a.m.
f=18cm means that it has a focal length of 18cm, or 180mm. 1:2.5 is the max aperture, which is f2.5.
Dan Fromm , Jul 14, 2006; 10:10 a.m.
Y'r listing is incorrect. The lens is an 18 cm (= 180 mm) f/2.5. That's what f=18cm and 1:2.5 mean. Nikkor-H indicates that it is a six element lens. The newer 180 Nikkors are, I think, 5 element lenses.
The 180/2.5 was made for Nikon rangefinder cameras. It can be mounted on Nikon SLRs with an N-F adapter.
Old lens, more a collector's item than a user. I have no idea how much it will sell for.
Michael R. Freeman 
, Jul 14, 2006; 10:19 a.m.
"Is it a 50mm 35mm?" -- No. It's a lens for a 35mm rangefinder camera, but not a 50mm. It's a 180mm lens, for Nikon 35mm rangefinder cameras.
"What does the 1:2.5 and f=18cm mean?" -- 1:2.5 is the maximum aperture, in this case f/2.5. f=18cm is the focal length. In this case, 18cm (180mm).
Take a look at this scan from Peter Brazcho's book (please copy to your hard drive, as I will not leave it up for more than a few days). It should be helpful. Ignore everything after "The large Nikkor 180mm f/2.5 ..." at the bottom of the page. http://imagehost.vendio.com/preview/mi/mikerfns/18cm_Nikkor.jpg
I would list it in a more appropriate category, where you will get better exposure. Specifically "Cameras & Photo > Lenses & Filters > Film Camera Lenses > For 35mm Rangefinder"
Vivek . 
, Jul 14, 2006; 03:14 p.m.
"Will ship only to the U.S." Shooting yourself in the feet.
Kelly Flanigan 
, Jul 14, 2006; 10:52 p.m.
The 18cm F2.5 and 180mm F2.5 are short mount Nikkor-H lenses for the Nikon S rangefinder AND the Nikon F. You use a Nikon N-F adapter when using in on a Nikon F. The 180mm F2.5 is 6 elements in 4 groups, a single coated lens with a tripod socket too. It uses a 82mm filter, or 85mm slip on. This lens weighs 60oz, 1.7Kg. Its a PRESET lens, with NO automatic diaphram. In optical terms this is NOT a telephoto lens design, is not a compact lens design. When used with its tripod adapter and NO camera body, the lens is really cantilevered alot, and can dump down it the tripod is not tight. This can happen when switching bodies.
Kelly Flanigan , Jul 14, 2006; 10:59 p.m.
There is also a 250mm F4 Nikkor-Q preset, 350mm F4.5, 500mm F5 for Nikon S and Nikon F in "short mount" too.,
The 300mm F4.5 Auto nikkor for the Nikon F is only about 50mm longer than the 180mm F2.5 when both are side by side mounted on cameras!
Kelly Flanigan , Jul 14, 2006; 11:02 p.m.
The 500mm F5 short mount is a triplet, and weighs about 20 lbs with a camera attached.
