bennison@clt.DEC (Victor Bennison - DTN 381-2156) (12/26/85)
---
Thanks to the several of you who responded to my request for info on
Nikon lenses. I ordered the 55mm micro and the 28mm f2.8. I just
received them yesterday. I'm curious about some things. All my
Nikon lenses, the above mentioned and my 50mm f1.8 series E, exhibit
noticable pincushion (is that the right term?). When I look at a long
straight line (counter-top, ceiling line), and try to put the line
exactly along the bottom of the viewfinder, it arches slightly into
viewfinder in the middle. Is this normal? I note that my Kiron
28-85 f2.8 when set at the 28mm setting exhibits NO noticable
pincushion. Should I be really impressed with my Kiron? I thought
Nikkor lenses were supposed to be great lenses. Am I confused or
what? I do notice that the Nikkor 28mm is brighter then the Kiron at the
28mm setting. Looking at the same scene at the same aperture setting,
the Nikkor lets more light through according to my light meter.
Am I correct in assuming that f2.8 refers to the SIZE of the opening
and that the brightness is a function of how much glass is between the
light meter and the subject? I also notice that the Nikkor 28 focuses
to very short distances. In fact, with my Vivitar 2X macro teleconverter
and the 28mm Nikkor, I seem to be getting better then 1:1.
Vick Bennison
...decvax!decwrl!rhea!tools!bennison
(603) 881-2156darrelj@sdcrdcf.UUCP (Darrel VanBuer) (01/02/86)
In article <174@decwrl.DEC.COM> bennison@clt.DEC (Victor Bennison - DTN 381-2156) writes: >--- >... I'm curious about some things. All my >Nikon lenses, the above mentioned and my 50mm f1.8 series E, exhibit >noticable pincushion (is that the right term?). ...line >exactly along the bottom of the viewfinder, it arches slightly into >viewfinder in the middle. Is this normal? I note that my Kiron >28-85 f2.8 when set at the 28mm setting exhibits NO noticable >pincushion. Should I be really impressed with my Kiron? I thought >Nikkor lenses were supposed to be great lenses. Am I confused or >what? This prompted a quick experiment with a Nikon FE2, Nikkormat FTN and ground glass in the film plane. Results: a Nikkor 28/2.8 showed noticable pincushion in the FE2 finder, slight pincushion in the Nikkormat finder and almost none at the film plane (even a 135/2.8 Nikkor shows pincushion in the FE2 finder!! and tele's seldom have such problems). I suspect a combination of framing mask which is not in the same plane as the focusing screen and the strong lenses used to bring most of the light to your eye. >I do notice that the Nikkor 28mm is brighter then the Kiron at the >28mm setting. Am I correct in assuming that f2.8 refers to the SIZE of the >opening and that the brightness is a function of how much glass is between >the light meter and the subject? Yes, the f stop is the ratio of the effective light gathering aperature to focal length. In extreme lens designs, there may be no real aperature of that size, only the projection of a virtual aperature that size. Lenses T stop (transmission based speed) varies from the real F stop for a number of reasons: large number of elements (with attendant reflection loss), extent of lens coating, manufacturers' rounding biases (e.g. suppose it's really 2.93 --would you call that 2.8 or 3.2 standard marking). Even age of lens design may: before wide use of TTL meters, there was a tendency to round smaller to compensate for other losses. > > Vick Bennison > ...decvax!decwrl!rhea!tools!bennison > (603) 881-2156 -- Darrel J. Van Buer, PhD System Development Corp. 2525 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua} !sdcrdcf!darrelj VANBUER@USC-ECL.ARPA