Enlargement Exposure Scaling

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Ian-Barber

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If my target print is say 8x10 but I am doing test exposure prints on say 7x5, is there a way to work out the final exposure for the 8x10 after you have everything worked out on the 7x5 test print without having to go through the whole process again after scaling up to 8x10
 
I expect most of us do produce new test strips. There is an Ilford enlarging exposure meter which would allow you to take a measurement of (say) a particular highlight, then scale up and open the aperture to give the same reading. I guess it would get you pretty close and save some paper? However, I prefer to keep my aperture the same.
 
I also suggest to make new test strips.
Using a darkroom exposure meter can help, Hauck trialux or Kaiser Trialux which I highly recommend.
 
I would strongly suggest working at whatever the final print size will be because, in my experience, prints seem to lose contrast as they get bigger. This may simply be a "trick to the eye", but, for me, I like seeing a work print at its final size.
 
Some enlargers have scales, my Dursts do, these allow simple calculations.

I use to do a small print as well as a 16x12 (my main print size) and there was a direct factor in terms of time/f-stop, just coincidence I think, I still did a test though. The larger prints came first, the smaller were for scanning etc.

Ian
 
Yes, there is. You can use the inverse square law to calculate a new exposure.
However, it's the experience of most printers that altering the size of a print alters the look of it in some way, as Alan points out. Certainly, a calculation could help, but a new test strip would almost certainly be better.
 
Thanks, at this early stage for me in the darkroom, I will stick to new test strips, I have enough things to be thinking of :)
 
Ian, there are enough unseen variables in darkroom printing without introducing another one by doing test strips from one box of paper at a given size, then the final print from another box of paper at a different column height. Paper does vary from box to box. My advice would be to stick with one box, and, as others have said, keep the enlarger head at the finished print height when doing tests.
Nothing to stop you doing tests and work prints at a given height, taking your time to evaluate these, then coming back later to do "fine exhibition prints" to a larger size, though you would still need to start from scratch with test strips to find the correct exposure for the larger size.

Alan
 
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