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Old 16th May 2020, 07:27 PM
John King John King is offline
Join Date: Nov 2012
Location: County Durham
Posts: 2,158

Originally Posted by Martin Aislabie View Post
The edge effect actually called acutance - and is a well known affect when using very dilute developer.

Due to the increased developer activity along the edge - the theory being the developer in the undeveloped area helps replenish the spent developer working locally in the developed part.
I wrote an article which was printed in the AP about 25 years or even more ago where I described the effect of Rodinal developing a film at
1-50. I do remember for payment I got 75 and a box full of Kodak colour film

The photographs in FP4 were quite grainy (also due to the edge effect) and the subject was electricity pylons and cables against a deep blue sky which emphasised the very fine, clear line between the dark and light tones - very similar to the effect that you get with the unsharp mask with Adobe

The edge effect is also the reason unless you adore grain it should not be used to develop films of 200 iso or greater. If you think that may be excessive I tried it once with Kodak High Speed infra red. It was like a pebbledash wall. It almost had physical texture.
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