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 a 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.

 

[Nicholas Lindan]

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....This won't work for changing filters...

The method in the application note doesn't use metering, and it accommodates filter changes. It's not that long a read.

 

[RalphLambrecht]

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

if you use f/stop timing then, you can use your printin records from any size and paper to any other combination, but you need to do one test strip to get a new base exposure. All the other printing notes are relative to the base exposure and still apply!

 

[Nicholas Lindan]

[you] need to do one test strip to get a new base exposure [for the final print}

Well, not really ...

• A big problem is matching the contrast of the two prints. You won't find the matching contrast filter without an awfully large number of test strips (obviously, with experience the need for test strips decreases). However, if you have the HD curves for the two papers, then matching the contrast of the two prints the work print's curve in the area of interest becomes simple. This gives you the VC filter information for the new print. it becomes a simple matter of finding the right filter to match the contrasts of the two prints. Takes all of five seconds.
• Given the tone you want to hold constant across the two prints then the HD information on the two papers will give you the needed exposure change for the new prints. Another 5 seconds.
• And, finally, there is the exposure adjustment required by changing the size of the two prints. With a ruler provided by Darkroom Automation this also becomes a trivial task.

Add up the exposure corrections (they are in stops) and look up the required time multiplier on the back of the ruler. If you have an f-stop timer then you can enter the exposure correction directly into the timer.

Nary a test strip in site.

If this sounds intriguing, the application note on the Darkroom Automation web site goes into the details.

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