[pure-silver] Re: 35mm (started with Film in Dektol)
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 18 Nov 2009 14:27:43 -0800
----- Original Message -----
From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, November 18, 2009 9:49 AM
Subject: [pure-silver] Re: 35mm (started with Film in
Dektol)
Elias
I don't think, he said they 'have' less. He said they
'need' less,
which is correct.
Resolution test results highly depend on your test
procedure, so,
absolute values have to be taken with caution, but if you
keep all
other variables constant, you'll get a good relative
comparison. Most
my Hasselblad lenses peak around 60-65 lp/mm. My Mamiya 6
lenses reach
up to 90 lp/mm. My Nikon lenses perform between 70-100
lp/mm. Maybe
better 35mm equipment (Leica?) could do better, but I'm
afraid my film
is the bottleneck. I use Tmax-100 in ID11 1+1 with a 100:1
contrast
target. My estimate is that this combination is not able
to give me
much more than 125 lp/mm anyway.
You see why my MF equipment runs circles around my 35mm
equipment; not
much less resolution but less magnification in the
darkroom.
Regards
Ralph W. Lambrecht
http://www.darkroomagic.com
Keep in mind that the resolution of a picture is a
combination of the individual resolution of the lens,
negative, and print medium. The latter is seldom a real
factor. The rule of thumb for combined resolution is 1/T =
1/L + 1/F where T=total, L=lens, F=film. This is only very
approximate since the actual resolution requires convolving
two or more curves.
Also note that lens resolution varies with image angle
and is different for the radial and tangential fields and,
of course, with the stop. In general, the larger the stop
the greater will be the resolution, if one discounts lens
aberrations. Since some important aberrations are
proportional to the stop there is usually an optimum stop at
which the resolution is highest. There is even more to this
so that resolution numbers are far from being absolute.
While some aberrations scale with the lens focal length
the diffraction limit is a function of the aperture only.
That is, all f/2.8 lenses have the same diffraction limit
regardless of focal length.
A combination of 60 lp/mm is outstanding and difficult
of achievment.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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