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 (sold out?) may sell you a very nice working and well-supported unit. I will not sell you a timer, but I usually have circuit boards for sale for those who want to assemble their own. This is open hardware and software so you can build one using the design files provided here; you don't need to buy anything from me.

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.

assembled timer

WTF is an F/Stop Timer?

This is an enlarger timer. It controls (through duration of exposure) 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. And of course the timer does all the arithmetic for you. It can also be used to make colour prints, but it will do no colour computations for you.

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. All of that is taken care of by an f/stop timer, including the ability to program complex (up to 8 steps) sequences of dodge/burn actions into the 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 - even though the process has NOTHING to do with apertures except the logarithmic spacing of the values used.

Here's a brief article explaining what f/stop timing is all about and here's a primer from RHD (the manufacturer of another of these timers).


What it does:

New in Hardware (PCB) Rev.B (March 2014):

New in Software Version 0.6 (Jan 2015):

New in Software Version 0.5 (April 2014):

New in Software Version 0.4 (June 2012):

Features "coming soon" (for values of soon that include I-hope-someone-else-sends-me-a-software-patch):

The "not implemented" features have placeholders in the code and they may appear in the next few years. Missing features that are likely to stay missing for the foreseeable future are:

Demonstration Videos

A pretty good demonstration that being a stills photographer doesn't mean you can do videography, and that programmers should never be trusted with a dremel.

Construction and Use

See also:

© 2014 William Brodie-Tyrrell
Open Hardware