----- Original Message -----
From: "Bob Adler" <rgacpa@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, April 26, 2005 6:23 PM
Subject: [pure-silver] Re: Development modifications for
higher sharpness
> Much better!
> I look forward to reading the original...
> Thanks,
> Bob
Actually it was a setting in Outlook Express which got
accidently set to send MIME in Base-64. It is now reset to
send plain text with no encoding whatever.
>
> As I understand it, you get sharper images from thinner
> negs or negs processed in weak developer because the depth
> of development in the grain of the film is less, resulting
> in less difraction of the light as you look at the neg or
> print it. High accutance developers like Buetlers are
> very low energy, and then you add potassium iodide to
> cause the edge affect to enhance the appearance of
> sharpness. The emulsion of ACROS lies so flat and
> grainless that it is probably difficult to change it much.
> I am on vacation at the moment with a brick of 120 ACROS
> and when I get back to the lab I am going to try
> processing it all in PMK.. even though the new films like
> that are not supposed to stain very well. YOu might try
> your fuji 400 in the PMK or some pyro developer.
> D Purdy
>
>
This has to do with resolution not acutance. Acutance is
a Kodak term for _appearant_ sharpness. It is an optical
illusion caused by accentuating the contrast at edges
between high and low density areas. This effect is caused by
reaction products of the developer in the high density areas
diffusing across to the low density area and affecting the
rate of development there. It varies with the properties of
the developer and the emulsion. In general, diluted
developers and lack of agitation tend to cause this effect,
which is also classified as edge or border effects. A
microdensitomiter trace through a sharp edge will show a
small peak on the high density side and sometimes a small
depression on the low density side. The gradient of the edge
tends to be increased.
Compensation is the creation of a shoulder or low
contrast area at higher densities. This is also caused by an
accumulation of developer reaction products in the denser
areas. Again, it is dependant on the developer properties
and emulsion. The same sorts of developers which exagerate
edge/border effects can also produce some compensation.
Usually, these are diluted developers with a single
developing agent and not too much sulfite. The properties
needed to produce both effects seems to be opposite to those
needed for low grain.
Acutance does not increase _resolution_. In fact, the
distortion of the reproduction of edges tends to reduce
resolution a little. However, the eye sees acutance as
sharpness rather than resolution.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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