F-Stop Printing

21 May 2010

When shooting our photographs, we all think in f-stops and zones, but when we step into the dark room, all of those principles are thrown out the window. The silly thing is, every single one of those principles apply in almost the exact same way. Paper is exposed exactly the same, add one stop of light, and you’ll get one more zone, subtract a stop and you’ll drop by one zone on your paper. Then why the heck do we think in time instead of stops? Well, because that’s what most of our timers give us. Until you get one of these. This is a timer that sets an inital “time” but then works in stops from there. Is the print too light, add a stop, or want to darken one area of the print by 1/2 a zone, then add 1/2 a stop, not 32.5 seconds.

Lets think about our test strips for s second.

Most of us create the following test strip:

5 sec 10 sec 15 sec 20 sec 25 sec 30 sec

The difference between steps 1 and 2 is 1 stop. Awesome. What about 2 -> 3? Well, to be one stop, we’d need to double, and we’re not quite doing that. By the time we get to the end, the difference between steps is pretty minimal. In fact, 25 -> 30sec is only about 1/4 of a stop. Great if you need to burn something but pretty useless as test strip time.

Time Example:

For our first try, we’re going to do an 8x10:

  • 10 seconds looked good for our main subject, but we need to dodge the background a bit. We have to do another test to find out where we want background to look. Test determines it looks good at 3 seconds.
  • But now we want to do a 20x24
  • 73 seconds looked good for our main subject, but we know the background needs to be done. Well, we have to do our background test all over again. This time we find it looks good at 30 seconds dodge.

If we used f-stop type times, then think about the following test strip:

5.6 sec 8 sec 11 sec 16 sec 22 sec 32 sec

Hey, wait a second, those numbers look somewhat familiar. We’ve increased our time in 1/2 stops and the spacing between each step is much more even! Now, lets take the example that we have a 8x10 print where the main center of focus looks good at at 11 seconds, but our background is really dark, and looks best at 5.6 seconds. Well, we know we need to dodge 1 stop. But now, we want to make a 20x24. Crap, we need to redo our test strip, and redo everything. Not really, we only need to get our main time, and know that we still need to dodge the background 1 stop. Sweet! We just saved ourselves a lot of time.

This can be done without an F-Stop timer, it just takes a bit more work. You’ll need to refer to an F-Stop chart to determine your times.

As far as I’ve found, there is only one F-Stop timer manufacturer, RH Designs based out of England.