There was actually relatively poor quality control from many lens makers well into the 60s and 70s; factory tolerances told the story. Until automation yielded tighter manufacturing tolerances for overseas makers, which really began in the 70s but did not become wide-spread till the 80s, there was very significant individual variation from even the best manufacturers... Eric Goldstein -- On 11/4/07, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote: > > ----- Original Message ----- > From: "Douglas Nygren" <dnygr@xxxxxxxxxx> > To: <rollei_list@xxxxxxxxxxxxx> > Sent: Sunday, November 04, 2007 8:51 AM > Subject: [rollei_list] Re: changing lens formulas > > > > Interesting thread, this. Let me add a point or two. > > > > A friend with an old Zeiss lens showed me a mark next to > > an F stop. He said that probably came from the factory. He > > explained that at one point the factory would pre-test > > lenses and mark the sweet spot. I don't know if that's > > true or not. > > > > My experience with a relatively new Zeiss lens on a Contax > > MF 645 was that one particular lens was disappointing > > except at one certain F-stop, where it is terrific. > > People have a three-dimensionality to them. > > > > Until I found that spot, I used to curse myself for having > > bought it. Now I'm glad I did. > > > > Doug > > > Unless one has access to factory archives its almost > impossible to tell what the prescription for a given lens is > beyond its generic type. There are perhaps a dozen or more > patents from Zeiss Jena on Tessar type lenses including a > few clearly experimental ones and some others from C.Z. in > Oberchoken. Add to this perhaps a hundred patents on Tessar > types from other manufacturers and you have some idea of how > difficult it is to identify a particular commercial lens as > being a particular prescription. Also, not all design > variations were patentable. > It is certainly true that there was relatively poor > quality control of lenses up to WW-2. That was improved by > the major manufacturers in both the U.S. and Germany after > the war because war-time work required that a higher > standard be applied. However, there is still a lot of > variation between individual samples. > To evaluate a lens requires that the aerial image be > examined. This eliminates a lot of variables such as all the > mechanical problems of a camera and the variables introduced > by film. It is not too difficult to see at least major > faults in a lens this way. Tests made in a camera actually > test the entire camera and are subject to inaccuracies in > focus and variations in the film plane. > There is a tremendous amount of rumor about lenses and > their design, mostly without any means of substantiating it. > Some of it makes no sense in light of the fundamentals of > optics and design. > > --- > Richard Knoppow > Los Angeles, CA, USA > dickburk@xxxxxxxxxxxxx > > --- > Rollei List > > - Post to rollei_list@xxxxxxxxxxxxx > > - Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe' > in the subject field OR by logging into www.freelists.org > > - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with > 'unsubscribe' in the subject field OR by logging into www.freelists.org > > - Online, searchable archives are available at > //www.freelists.org/archives/rollei_list > > --- Rollei List - Post to rollei_list@xxxxxxxxxxxxx - Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe' in the subject field OR by logging into www.freelists.org - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with 'unsubscribe' in the subject field OR by logging into www.freelists.org - Online, searchable archives are available at //www.freelists.org/archives/rollei_list