home *** CD-ROM | disk | FTP | other *** search
- Newsgroups: rec.photo
- Path: sparky!uunet!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!cbnewsm!ka1gt
- From: ka1gt@cbnewsm.cb.att.com (robert.m.atkins)
- Subject: Re: Resolution of Lens ???
- Organization: AT&T
- Distribution: na
- Date: Fri, 20 Nov 1992 18:28:43 GMT
- Message-ID: <1992Nov20.182843.11017@cbnewsm.cb.att.com>
- References: <Bxw69K.309@world.std.com> <1992Nov19.025409.2162@walter.bellcore.com> <1ehhb7INNms3@hpsdlss3.sdd.hp.com>
- Lines: 42
-
- In article <1ehhb7INNms3@hpsdlss3.sdd.hp.com>, johno@sdd.hp.com (John Ongtooguk) writes:
- > |> In article <1992Nov20.003420.15573@cbnewsm.cb.att.com>, ka1gt@cbnewsm.cb.att.com (robert.m.atkins) writes:
- >
- > |> A couple of other points come to mind. (1) At the resolution limit the
- > |> image of the test target is no longer high contrast (the aerial image
- > |> that is). The resolving power of Tech Pan is only 125 lp/mm for low
- > |> contrast targets (usually 1:1.6?). Thus as you approach the resolving
- > |> limit of the lens, the resolving power of the film itself drops also.
- > |> Thus if the lens JUST resolved 400 lp/mm in a low contrast aerial
- > |> image, 125 lp/mm from the film would give only 95lp/mm on the negative.
- >
- > Good point. I recall an ad (with no data to back it up) that stated
- > that the resolution of the new Leica 105mm apo-macro exceeded the
- > resolving power of Tech Pan. It or the Nikon 105 apo process lens
- > might be the tools you need to test your theory as you should be
- > able to record a high value that drops off quickly as you stop down.
-
- Thinking more about the problem, I'm sure this is in fact the answer.
- Taking the observation that I can get no more than about 80 lp/mm from
- my diffraction limited f5 lens on Velvia as a starting point:
- (1) The USAF target requires about 20% modulation to be "resolved" in an
- image according to an old copy of "Modern Photography"
- (2) The MTF curve of Velvia (from Fuji literature) suggests that the MTF
- at 80 cyc/mm is MAYBE 25% (from an optimistic extrapolation of their data
- which only goes to about 60 cycles/mm).
- (3) At 80 cycles/mm the MTF of a perfect f5 lens is about 70%
-
- The modulation in the image is the product of the MTF of the film and the
- MTF of the lens, so at 80 cycles/mm = .25 x .7 = .175 (17.5%) which is
- right on the threashold of visibility.
-
- So this lens should give a maximum of about 80 lp/mm (neglecting differences
- between square wave modulation in the target and MTF values based on
- cycles/mm or sinusoidal modulation).
-
- I'll check my literature to see if I can find MTF data on Tech Pan and see
- what I should be able to resove on it.
-
- ===============================================================
- Bob Atkins AT&T Bell Labs email (direct) att!clockwise!rma
- ===============================================================
-
-