How To: F-stop Print
Some can find f-stop printing to be confusing but it really needn't be. In fact, once you have got your head around the principles behind it, it really makes sense. I mean, we operate our cameras in terms of f-stops, so why don't we do the same when enlarging? For many, doing tests strips in seconds works for them and they are happy with that so fair enough. I'm just going to present f-stop printing to you and let you make your own choice.
So what is it? Basically, instead of exposing test strips and dodging and burning in terms of seconds we do it in terms of f-stops. This means that should we need to make a larger print at some point in the future we can just adjust the base exposure and maintain the f-stop values instead of having to recalculate each dodge and burn in terms of seconds. It's easier to explain with an f-stop printing chart:
At first glance this may seem confusing but it is relatively simple to suss out. Times are given in terms of 1 stop (dark grey), 1/3 of a stop (not quite as dark grey), 1/6 of a stop (light grey) and 1/12 of a stop (mid grey).
So let's start at the beginning and say you're doing a test strip. Instead of going from 1-30 seconds for example, using the f-stop chart you could go in intervals of 1/3 of a stop, so you would go 8.0, 10.1, 12.7, 16.0, 20.2, 25.4, and 32.0 seconds. What are the advantages of this? Well, each strip on your test strip will have exactly the same amount of light added to it at each strip (in this case 1/3 of a stop). If you were to do a strip merely in seconds then you would not get this uniformity. The f-stop method makes it much easier to pick out your base exposure as, just like when you are exposing your film, every extra stop of light you add is double the amount of the previous stop.
There are dedicated f-stop timers out there that automate the process for you but they are pricey. I used to use a Paterson timer which allowed me to input increments of time in 0.1 of a second from 0-9 seconds and then 1.0 seconds thereafter. This meant i have to do a bit of fiddling about to do a test strip but i found it was worth it. I now have an RH Designs timer which I got from Ebay and I wouldn't trade it for anything, it has revolutionised my printing method.
When it comes to dodging and burning the f-stop printing method is a life saver. Let's say your base exposure is 18.0 seconds and you want to burn a sky in for 1 full stop extra. Just look up 18.0 under the B (base exposure) column and move right to the +1 column which says 18.0. That means to add an extra stop you need to expose for another 18.0 seconds. +1/2 a stop would be +7.4 seconds and so on.
This comes in handy when resizing a print. To make a bigger print the enlarger head needs to be higher. As the enlarger head is higher exposures will be longer. So say were taking the same print and were going from 8 x 10 to 9.5 x 12 and our base exposure has gone from 18.0 seconds to 22.6 seconds. Instead of using formulae to try and figure out what our new dodging and burning times would be as we recorded them in terms of seconds, we know that our dodges and burns will stay the same in terms of f-stop. So if we have a +1/3 of a stop burn at 18.0 seconds base exposure (+4.7 seconds) at our new base exposure of 22.6 seconds this becomes +5.9 seconds. Follow all your recorded dodging and burning times and voila - the same print but bigger!
It sounds complicated but if you re-read this article a few times and you'll get the hang of it. It really is worthwhile to try out and it may well revolutionise your printing!