Optical Slaves are the simplest (and cheapest for the most part) method for using off camera flashes.

The principle is simple, when the optical slave sees another flash fire, it fires too. Kinda like yawning. Once one of goes, it is catchy.

Of course optical slaves have their limitations, one of which is that they are too dump to understand the difference between a flash and a pre-flash. There are a few more limitations to optical dumb slaves, but this post is about overcoming the pre-flash issue with a cool gizmo called Arduino.

What is Arduino?

Arduino is an open source software and hardware development platform. This means that anyone can start off with an Arduino board and kinda quickly develop an application that requires both hardware and software with very little effort. Here is a very good intro from Make!

Now, How About Them Smart Optical Slaves

Here comes the part where I completely fall of my feet for open source. So Digital Photography Tips and Techniques (or dptnt) took up one of those boards and started playing around with it. The outcome, an optical slave that is not afraid of pre-flashes.

There are some assumptions to the model like the time delta between the pre-flashes and the “real” flash, but for most scenarios it should work.

This is where the open-sourceness of this really rocks. I’ve been an embedded engineer for about 10 years now. This platform is so quick to start developing it will make your head spin. If there are any fellow embedded engs reading this, you’ll probably appreciate how fast it takes to bring those up.

The other cool thing is that DPTNT released the code, to the community so anyone can cheap in and add features, fix bugs, or learn about how this works.

Some More Limitations with Optical Slaves

Even a biffed up optical slaves still suffers from the basic limitations that lies at the base of the optical slave triggering system: it is optical.

The first limitation is that as with any optical solution, the trigger needs to be in line of sight with the “master” flash. This means that you cannot trigger around corners, from indoors to outdoors or from anywhere that you don’t have a line of sight.

The other limitation is about light difference in general. It is hard for an optical slave to sense a fellow flash when it is in a bright light, say a sun lit location.

And the last issue is that an optical slave is prone to the auntie attack – that means that every aunt with a point&shoot that has a flash on will trigger your optical slave as well. This is not really an issue if you are a solo photog at your studio, but it can really drain your flash if you are at a wedding with lots and lots of aunties.

One solution for this is to use a Radio Controlled Slave like PocketWizard , but I will leave this discussion for a different post.