DIY F/Stop Timer
This webpage shows how you can build an f/stop timer for B&W analogue printing. If you just want to buy one, both RHD and DA will sell you a very nice working and well-supported unit. I will not sell you a timer.
If you build this, please contact me (email address is in the headers of all the source files) as I'd like to have some idea of how many of these are out there. Of course if you have suggestions or bug reports, please send them in too.
WTF is an F/Stop Timer?
The term "f/stop timer" was coined by Gene Nocon, who is widely credited with inventing this approach. Nocon sold an f/stop timer and more importantly, called it an f/stop timer. Here's a video where Gene discusses f/stop printing and a bit of printing history.
To take a step back, this is an enlarger timer. It controls how much light hits a piece of black and white photographic paper, thereby controlling how dark it gets. By expressing exposures in a log scale (stops, being log base 2), we can perform a lot of print manipulations such as dodging and burning, changing size, shifting the image by a fixed overall tone change, etc, just by performing simple addition/subtraction arithmetic.
While you can achieve the same ends with a linear timer, it's a lot more taxing, both in the number crunching you have to do in your head as well as needing to adjust the times for all exposures in a print when making a global adjustment, e.g. for print magnification.
Regardless of the f/stop thing, it's also handy to be able to program in a whole exposure sequence for a print instead of needing to remember the sequence and set the times one-by-one.
What it does:
New in Version 0.4 (June 2012):
The "not implemented" features have placeholders in the code and they should appear in the next few months. Missing features that are likely to stay missing for the foreseeable future are:
Construction and Use