Exposure correction when BOTH size and paper change

[Nicholas Lindan]

There is a new application note on Darkroom Automation's web site that describes a method for finding the required exposure change when moving from a small work print on one paper to a final large print on a different paper. Test strips, f-Stop timers or enlarging meters are not needed. The only tool required is a yardstick, and even that is optional.

Yeah, yeah. I know - we just went through an interminable thread on changing print size. But this application note is also about how to adjust both enlarging exposure and VC filtration when changing papers.

http://www.darkroomautomation.com/support/Resizing.pdf

 

[xkaes]

I know how frustrating this "simple task" can be. There are lots of approaches. Mine is to use a hand-held meter with an enlarging attachment, but a color analyzer or simple enlarging meter will work too.

The first thing I do is determine an ISO for my papers -- without any filters. Let's say you like to expose your papers for 30 seconds. Then make a good print on paper X at whatever f-stop gets you close to 30 seconds. Take the negative out and read the white light -- and adjust the meter to that f-stop and whatever time you exposed it for. That's the "ISO" speed for that paper -- and you can use any other f-stop & speed that the meter gives you.

If you adjust the height of the enlarger, you just take another reading at that paper speed -- without the negative -- and select the time & f-stop you want.

If you change paper, you need to first determine an paper speed for that paper -- and adjust the meter -- whether or not you adjust the height.

This won't work for changing filters, however, just changing the height and the paper -- both at the same time.