*sigh* I wanted to have this done yesterday but I got caught up in a few things and well here is today. Ahh, close enough.
The first part of my flash mini-series is quite straight forward, but I do have a few points to mention.
First up I'll quickly mention the links that I scrounged up. If you're the tinkering type you might like the first couple of links on how flashes actually work. Then I've included some URLs to websites that explain the guide number in more detail. Now as mentioned in my video, unless you really enjoy doing math in your head or are using manual flashes for your work, the majority of digital SLRs and electronic flashes today do all that good stuff for you. Thus, you can just point and shoot and in most cases get an adequate exposure when using a flash.
Second up is in regard to getting the right flash for your camera. Sometimes mixing brands are not a good idea as the camera body may not be able to properly communicate with the flash. For example, my Olympus E-3 can control the FL-50 flash I have (also Olympus), including its ability to zoom, but if I used another make of flash then I might only be able to use it in manual mode; in other words, I better know my guide number formulas as the camera body will only be able to trigger the flash, not tell it what power to use (or how much to zoom, to use the auto-focus assist illuminator when the shutter button is half-pressed, etc.).
Third up has to do with zooming. Certain flashes have the ability to focus their beam of light, or concentrate it if you will, when you use a telephoto lens and pull in on your subject. On my FL-50 I can hear a quiet buzzing sound as a micro-motor activates and moves the flash's innards around. Also, because the beam of light is more focused compared to the wide setting, manufacturers usually base the guide number off the zoomed setting (mostly a marketing thing as far as I can figure; big numbers look better). This is good to keep in mind because if you're primarily doing wide angle shooting then you will get somewhat less light out of your flash.
So there ya have it! Stayed tuned for the second part of my flash mini-series, which will focus on the flash sync speed. As usual, please subscribe and check me out on Facebook (become a Fan!) to stay up-to-date with my videos and other stuffs. L8r!