[pure-silver] Re: lens resolution
- From: "Ole Tjugen" <ole@xxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sun, 13 Jan 2008 19:20:20 +0100
With a view camera, my opinion is that it doesn't matter.
I have a negative I shot with an 1890's (yes, eighteen ninties) 300mm lens
on 18x24cm film at f:45 - the lens doesn't have a shutter, so I needed to
stop down that far to get a 1/2 second exposure I could do with my hat. On
the negative using a microscope I can clearly see the white wood (what are
they called?) between the small panes in the windows on a farmhouse 6km
away. Since these are less than 6cm wide, that's 1:100000 of the distance.
The focal length of the lens was 300mm, or 1:20000 of the distance. so the
thickness of one of these lines on the negative should be 0.003mm, which
is far smaller than the estimated max resolution of any lens at f:45? I
assume the high contrast helped quite a bit here, since a resolution of
better than 160 lppmm is quite unrealistic. But it still illustrates the
point that resolution is not a concern with any good lens made in the last
130 years or so. :)
Ole Tjugen
På Sun, 13 Jan 2008 18:47:56 +0100, skrev Shannon Stoney
<shannonstoney@xxxxxxxxxxxxxxx>:
I guess I should pay attention to this, then, with my lenses that are
old? I have a Leica and a Rollei from the late thirties. The lens on
my hasselblad is from the late nineties. I don't know how old the used
lenses are that I use with my view cameras, but apparently it doesn't
matter?
--shannon
On Jan 12, 2008, at 8:13 PM, Vick Ko wrote:
It was true in the 80's. Max aperture was degraded by spherical
aberations, minimum aperture was degraded by diffraction. Sweet spot
was in the middle.
Now, with modern computations and aspherical lens generation, maximum
performation can be had at max aperture (e.g. all those Leica ASPH
lenses). Minimum aperture still comes with diffration effects.
How times change.
As for f64, f64 on a huge lens (e.g. LF lens) can still be away from
the point where diffraction degrades the image.
...Vick
From: Shannon Stoney <shannonstoney@xxxxxxxxxxxxxxx>
Reply-To: pure-silver@xxxxxxxxxxxxx
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] lens resolution
Date: Sat, 12 Jan 2008 20:05:17 -0600
I was looking at an old issue of Darkroom Techniques today, from the
early eighties. There are a lot of articles about grain, getting rid
of grain, whether grain is bad or not, etc. In one article, the
author says, "Virtually all lenses perform best somewhere near the
middle of their aperture range and worst at, and near, the extremes."
Is this true? I don't quite understand this. If this is true, why do
all those Ansel Adams and Weston prints shot at f/64 look so sharp?
Is it only true if you are enlarging 35mm negatives to 11x14 or larger?
(I understand that maybe it's not an issue at all with Weston's prints
because they were all contact printed.)
--shannon
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Ole Tjugen
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