[pure-silver] Re: Tonal gradation/smoothness in 35mm negs c.f. larger formats
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 14 Jan 2008 13:31:44 -0800
----- Original Message -----
From: "Peter Badcock" <peter.badcock@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, January 14, 2008 1:20 AM
Subject: [pure-silver] Re: Tonal gradation/smoothness in
35mm negs c.f. larger formats
Hi Richard,
thanks for your reply. It certainly sounds like the
difference in tonal
smoothness is more than just a minor thing as you say
"there is a noticeable
difference between 35mm negs and anything larger". In
fact you mentioned it
here
<//www.freelists.org/archives/pure-silver/09-2007/msg00098.html>a
few months ago in pure-silver.
I had also naively assumed that there were few good
reasons to use a low
accutance developer. So for 35mm it appears that there is
a trade-off
between accutance(sharpness) and tonal smoothness. This
was also a new
revelation for me.
I then realised that a chromogenic film like XP2 (which
has no grain, but
rather "dye clouds") inherently provides smoother
tonality. I did a quick
search and discovered a
post<http://photo.net/bboard/q-and-a-fetch-msg?msg_id=003EHC>by
Mark
Parsons to back up my deduction.
"This film (XP2) has very smooth tonal gradations, handles
highlights very
well, but seems to have very little edge effects. (High
resolution but low
apparent accutance - "fine" but not "sharp".) All of this
adds up to a film
that is (in my opinion) wonderful for most portraits and
other "soft"
scenes, but not the best for most landscapes and
architecture"
Here is one follow-on thought/question. If I then use a
low accutance
developer with a fine grain/high res film like 100T-Max or
Delta 100 in
order to get good smoothness, could I then improve
sharpness by unsharp
masking? (without losing tonal smoothness)
regards
Peter
Chromogenic film does have grain because the dye is
formed in proportion to the silver so the dye image mimics
the original silver image. Kodak distinguishes between
grain, which is a measurable quantity, and graniness, which
is a perceived characteristic. They published a short
treatice on that which I think is still on the Kodak web
site.
Acutance is a measure of perceived sharpness and is a
term invented by Kodak for it. They found that edge contrast
affected the perception of sharpness so that development in
a way that exagerated the contrast of edges in an image
would result in higher perceived sharpness. Acutance is not
the same as resolution and the edge effects which produce
acutance can actually reduce resolution. One reason low
grain developers might also be low acutance is that they
tend to have large amounts of sulfite. The main function of
sulfite in a developer is to oxidize preferentially to the
developing agent. Since edge effects are mostly the result
of local exhaustion effects high sulfite developers tend to
supress them.
Acutance is desirable mostly in small negatives to
compensate for lenses with low edge contrast or poor
resolution. When one has a sharp lens this compensation may
not be necessary or even desirable. Since the scale of the
edge effects on the film is fixed the acutance boost is
inversely proportional to the format size. Acutance effects
are very noticable on 35mm negatives but hardly at all for
4x5.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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