NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/rec/photo/20297

Text File | 1992-11-21 | 3.7 KB | 72 lines

Newsgroups: rec.photo
Path: sparky!uunet!spool.mu.edu!agate!ames!xn.ll.mit.edu!micro-heart-of-gold.mit.edu!news.media.mit.edu!news.media.mit.edu!monta
From: [e-mail] (Peter Monta)
Subject: Re: Resolution of Lens ???
In-Reply-To: [e-mail]'s message of Fri, 20 Nov 1992 00:34:20 GMT
Message-ID: <[e-mail]>
Sender: [e-mail] (USENET News System)
Organization: MIT Advanced Television Research Program
References: <[e-mail]> <[e-mail]>
    <[e-mail]>
    <[e-mail]>
Distribution: na
Date: Sun, 22 Nov 1992 04:48:01 GMT
Lines: 56

[e-mail] (robert.m.atkins) writes:

> ...  Depending on exactly what you define as resolution,
> a diffraction limited lens should resolve close to 1800/f-stop lp/mm. Lets
> be conservative and say only 1200/f-stop. That means a diffraction limited
> lens at f4 should resolve 300+ lp/mm, similarly 428 lp/mm at f2.8 or
> 215 lp/mm at f5.6. I know this is conservative since I can see a resolution
> of over 250 lp/mm from an f5 lens I have when looking at the aerial image
> (the formula would say 240 lp/mm).

Yes, aerial image means you really get to focus well; there are
apparently several unknowns when it comes time to expose film:
SLR focusing bias, film flatness, etc.  I'm not really sure how to
combat these, short of making some of the test equipment described
in "Dark Side of the Lens", or doing a lot of focus bracketing.

Coincidentally, I've just been reading some old microlithography
stuff---it's very interesting.  Even in 1968 people were realizing
500 lp/mm over centimeter fields, and the focusing arrangements were
draconian:  pneumatic gauges (!) seemed to be popular.  There's a
Kodak paper in "Ultra-microminiaturization:  precision photography for
electronic circuitry", SPSE proceedings, 1968, that talks about
a flexible testbed on the cheap, with microscope objectives.  Stevens,
"Micro-Photography", 1968, is also useful.  (I'm kind of wondering
if my library has anything more recent... :-))

> Well, if we believe Kodak at 320 lp/mm for Tech Pan (HC-110 dilution D
> development - which is what I use) then there should be no problem at
> all in getting 100 lp/mm. You would only need 145 lp/mm from the lens
> as you said. This should be easy, yet modern photography had GREAT
> trouble with the best lenses available. If you look at most of their
> tests lenses tended to top out at about only 70 lp/mm (though I never
> found a reference to exactly how they did their testing on on what type
> of film).

Well, I'm certainly not a lens type, but the trick for high
resolution/large field seems to be to design for one pair of
conjuagates and one wavelength.  A bit limiting for ordinary
photography.  I agree, though, that perhaps lenses should be topping
out at better than 70 lp/mm.

> 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.

Yes, the emulsion needs to be really good to evaluate 400 lp/mm kind
of performance.  The Lippmann-style emulsions, like Kodak's
high-resolution plate, holography films, etc., have very fine grain and
high contrast (hopelessly so for pictorial applications), which helps.

Peter Monta   [e-mail]
MIT Advanced Television Research Program