Relationship between film speed and developing time

Pieter12

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I accidentally exposed a roll of HP5+ at half the speed I usually do--exposed at ISO 80 rather than 160. I do not see a time for HP5+ at that speed and my usual developer on the Massive Development Chart. Can I just multiply the development time by some factor? Is there a formula for the relationship between film speed and development time?
 

Andrew O'Neill

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It's only a stop more than EI 160, so I wouldn't worry about it too much...but I have no idea what is on the film. I'm assuming it's roll film? Are they full scale images? A mixture? HP5 is my main film, by the way. I've accidentally over exposed film a bit and pulled back development time a wee bit and all was well.
 
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Pieter12

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It is 120 film, mostly studio still-life. I shoot mostly HP5+ at 160, develop in Rodinal 1+38 for 7:30. I think I'll give it a bit less than a minute less time?
 

RalphLambrecht

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I suggest cutting your normal development time by 25%(but not below 5 minutes) and enlarge on a much harder grade of paper.
 

Sirius Glass

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The film was exposed one f/stop from box speed which is well within the exposure latitude of the film. Develop normally.
 

MattKing

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80 vs. ISO of 400 - that is a fair amount of increased exposure.
I would be concerned about highlight rendition.
 

Andrew O'Neill

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MattKing said:
80 vs. ISO of 400 - that is a fair amount of increased exposure.
I would be concerned about highlight rendition.
Click to expand...

He normally exposes or at EI 160, so just a stop over for him. Curtailing development time a wee bit should take care of it. We don't know what contrasts we're dealing with so one can only guess.... I guess, lol
 
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