[rollei_list] Re: Does the Quality of a Lens Affect Grain?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 1 Dec 2008 13:29:46 -0800
----- Original Message -----
From: "Peter K." <peterk727@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, December 01, 2008 10:48 AM
Subject: [rollei_list] Re: Does the Quality of a Lens Affect
Grain?
Yes, more grainy. It is simply not resolving as well in many
instances
a result of not passing enough light (coatings) which can
result in
grain. I am sure there are those that may say otherwise, but
this is
my opinion.
On Sun, Nov 30, 2008 at 8:07 AM, Elias Roustom
<eroustom@xxxxxxxxxxx> wrote:
I know there's no comparison between the quality of the
lens on my Rollei 35
and my Rollei Giro 90, but is it possible that in addition
to difference in
contrast, the cheaper lens would make the images more
grainy (or less
smooth)?
E.
I think I understand what Peter is getting at but I
_do_ disagree with it. Film does not work that way. While
some film as more than one coating, generally to extend the
latitude. More modern emulsions achieve the same purpose
with a mixture of silver particals. Also, generally modern
emulsions are thinner than those of the past mostly to
improve sharpness. In the older, thick, emulsions, the light
striking the surface became diffused as it passed deeper
into the emulsion so that the image was sharp at the surface
but became more blurred as it went deeper. Of course, the
light also became attenuated as it was scattered so the
overall image remained pretty sharp. However, sharpness also
decreased with increasing exposure. This is the primary
reason the film speed system in use now (ISO standard
method) is designed to give the minimum exposure that will
result in good tone rendition.
Grain also varies with average density becoming greater
as the density increases, another reason for keeping
negatives on the thin side.
Now, its also true, and I think this may be what Peter
is getting at, that the sensitivity of the silver halide
grains, and the size of the image silver that develops from
them, varies with their size. The finer grains are less
sensitive than the coarser ones. Also, grain tends to
increase with development time. So, an underexposed negative
may look grainier than a properly developed one. If the
negatives from a blurry camera are being developed more than
those from a sharp camera in order to increase the apparent
contrast, that would also increase the grain.
There is something also in the idea that an image which
is confined strictly to the surface may look grainier than
one which extends into the emulsion a bit since what we see
as grain is actually the statistical combination of many
silver grains. When there are more to combine the imager
looks less grainy. Individual silver grains are nearly
submicroscopic and are not visible when using a grain
focuser on an enlarger. What is seen there is the "clumping"
of grains at various depths in the emulsion. The fact that
visible and printible grain is the result of a stochastic
process also explains why the Callier effect exists. Simply
that diffused light striking the emulsion on one side is
less likely to be blocked by the grains at various depths,
that is, by striking the surface at many angles, some will
be scattered and tunnel around the denser areas to wind up
going toward the lens where collimated light will be
scattered away from the optical path to the lens. All this
is to say that grain is a physical effect not affected
directly by the nature of the image or lens.
However, having said all that I agree more with the
idea that a blurry image may _look_ grainier than a sharp
one because the eye is more more likely to detect the grain
in areas of continuous tone especially in the mid grays.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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