[pure-silver] Re: PIQUED MY CURIOSITY; was Phenidone in alcohol
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 7 May 2009 18:54:58 -0700
----- Original Message -----
From: John Stafford
To: pure-silver@xxxxxxxxxxxxx
Sent: Thursday, May 07, 2009 2:29 PM
Subject: [pure-silver] Re: PIQUED MY CURIOSITY; was
Phenidone in alcohol
(forgive, but my web mail doesn't permit bottom replies)
I have never achieved edge effects through development.
Not in over forty years.
And perhaps I just don't know what to look for.
Could someone post an example, or Is it impossible to post
an example of edge effects?
John
I don't know of a web site with pictures. Edge/border/
effects or Mackie lines, and other names. These come from
localized variation in development. The usual explanation is
that the reaction products of development on either side of
a high contrast sharp demarcation enhance the contrast of
the line or point. In effect, a line is drawn around high
contrast parts of the image. Since the eye interprets high
contrast edges as sharpness these effects enhance the
property called by Kodak acutance. It is not the same has
high resolution and, in fact, acutance enhancement
generally reduces resolution a little by smearing closely
spaced fine details.
Another form of edge enhancement is produced by tanning
developers. The localized, imagewise, tanning causes the
index of refraction of the gelatin to vary and this also
produces local variations in apparent density.
All of these effects are minimised by the sulfite in
developers which tends to counteract the developer reaction
products, or, rather, to prevent their formation. Note that
both the tanning and staining from developers like Pyro and
hydroquinone are caused by reaction products of development
and sulfite tends to reduce or eliminate them.
To observe acutance effects try a developer like
Microdol-X, Perceptol, or D-76 diluted 1:3. Rodinal at
dilutions of more than about 1:50 also produces noticable
edge effects.
Since the effect is fixed in scale it is visible in
small format negatives but not in larger format when
magnified to the same extent. It is visible to some degree
in 120 negatives but not to the same degree as in 35mm ones.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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