Wednesday, March 30, 2011

F-stop printing

I wanted to share a darkroom technique that I use when I print that not many people seem to know about. It's called F-stop printing.

Now, this isn't something new, it's been around for a long time, but it's not what we are taught in school or in many photography books. When I was taught to make test strips, we'd make them based on multiples of seconds. So start at say 5 seconds, the next bit would be 10, the next 15 etc. I personally find this to be rather inefficient.

Instead, I do my test pieces (which are few - but that's another post) based on using stops. Just like when you factor in stops when you shoot, you can factor in stops when you print. A stop more is doubling the light, a stop less is halving it, regardless of whether you are exposing film or paper. So to begin, I'll pick a starting exposure in seconds based on a best guess, knowing what my paper, aperture etc tends to go with. For me, 10 sec to 20 sec, which is one full stop by the way, tends to cover my average negatives, and makes for easy calculations. This will be different for you and depend on your paper, your negatives and what aperture you choose. I use a very slow paper, Fomatone, which is a full two stops slower than Oriental for example, and commonly print at f8, if you are curious.

Next I simply divide that one stop range into quarter stops, so you get 10 sec, 12.5 sec, 15 sec, 17.5 sec and 20 sec. Now, someone is likely to pipe up at this point, that these aren't exact 1/4 stops, which is true, but they are close enough and a simple extra 2.5 sec from my starting time. If you want real quarter stops, from 10 to 20 it would be 10/11.9/14.1/16.8/20. See the unblinkingeye.com link below for a chart if you are picky. While I am very exact with measuring chemicals, 0.7 of a sec at this point isn't a big deal.

I then expose the test piece or strip accordingly. When I take a look, I can see which is closest to the exposure I need and since it is all roughly quarter stops apart, I can very accurately, off that one strip, pick a good exposure. No guessing, or fiddling around with a few more seconds, here, or a few less, taking several tries to get it narrowed down. Now it can be pretty close and sometimes hard to tell the bits apart, but you can always make it thirds or half stops, whatever works for you.

F-stop printing also helps when it comes to burning and dodging, as it makes things easier to decide. You can burn or dodge half a stop, a full stop etc.

Here's some further info to take a look at, including a couple of manufacturers of F-stop enlarger timers, which are on my wish list.


http://www.photovisionmagazine.com/articles/fstopprinting.html
http://unblinkingeye.com/Articles/TestExpo/testexpo.html
http://www.rhdesigns.co.uk/darkroom/html/f-stop_printing.html
http://www.darkroomautomation.com/fst-faq.htm

If you own Tim Rudman's The Master Photographer's Toning Book, (a previous post) there's a chart in the back. If you don't, what the heck are you waiting for?


Give this a try the next time you print. You might be surprised at how it simplifies things for you.

No comments:

Post a Comment