In a recent thread there was some discussion about using flash with a Sony, and I thought I'd share some experiences, and elaborate on what I've been using for certain parts of a wedding while working with the Sony A900s ... but it applies to any Sony with a hot-shoe and any situation where you'd like to experiment with lighting ... beyond what happens to be available.
The attached image below shows the basic equipment I take with me to a wedding shoot. Weddings present some more difficult ambient shooting conditions, and flash is often a necessity to get any image at all ... especially when there is subject movement.
First order of business is getting the key light OFF the camera to add more dimension to the image, (rather than flat, head-on lighting). The Key light is the main light that determines everything else.
To get the light off the camera, you need a way to trigger it. I use a Phottix Stratos-II radio system. IMO, the Sony built-in wireless trigger is semi-useless for all except the most rudimentary applications. It relies on line-of-sight infrared signals which are unreliable at distance and/or if there are objects blocking the signals.
The Phottix radio transmitter offers pass through TTL, so you can mount a Sony speed-light on-camera for TTL fill ... and that level of fill can be controlled by adjusting the flash compensation. The off-camera light doesn't receive TTL signals, so it must be set to either A or manual. This isn't as difficult as it sounds, since you usually only have to set it once, and everything else follows its lead. In dark conditions, I usually just set it to full manual unless I want to shoot close up or more wide open apertures. Most of the time the Key light is at distance or I am at distance, so I rarely use the off-camera light at less than 1/2 power.
In my attached gear photo I have one Sony speed-light mounted on a Sony mount Phottix Stratos-II receiver (A), and that is mounted to a Lowel Grip (G), so I can hold it up or low anywhere, or lay it down anywhere. The Sony fill-flash is mounted on a Phottix TTL transmitter (B), so the camera mounted light remains TTL, and self adjusts to the manually set off-camera light, no matter how it is set.
I also use a mobile boom arm (H) that extends to 9', with a Phottix Stratos-II receiver for Nikon attached (C), which then allows use of any speed-light with a conventional shoe mount ... in this case a Sunpak 120J bare-bulb speed-light (E) that takes all sorts of modifiers (F) including those for the Quantum Q flashes. You can do the same with a conventional light stand instead of a mobile boom arm if you are working alone.
The advantage of using an off-camera light such as the 120J as the Key Light, is that it does not suffer from the thermal limiter that will shut down a Sony, Canon or Nikon speed-light when repeatedly fired at full power, or close to full power. This also allows you to use a battery pack to insure fast recycle and lots of full power pops if needed ... such as the Quantum Turbo C that I use clamped to the boom arm or light stand (D).
The transmitter on the Sony will trigger a Nikon or Canon receiver, and a Nikon or Canon transmitter will fire a Sony receiver ... so you can mix and match almost any speed-light or studio strobe that has a Phottix receiver attached. The bottom gear shot shows a Sony and Nikon Stratos-II receiver being fired by a Nikon transmitter.
I use this basic set-up for maybe 30% of off-camera lighting. However, most people could use it for much more by increasing the ISO a bit. I don't because I like to shoot at lower ISOs therefore use more powerful lights ... either a 400 w/s Quadra, or Profoto 600B, or in more extreme situations, especially outdoors, a Hensel Porty 1200L. In comparison, a typical speed-light is about 70-80 w/s.
Hope this helps and maybe inspires some exploration of the possibilities with lighting ... using your existing speed-lights is a good place to start.
Here are a few off-camera applications from our most recent wedding. A "kiss portrait" outside in near dark, back-lit with one light and front fill with the on-camera light. The album page shows a couple of off-camera applications ... I shot the venue from outside and fired flash inside from quite a distance, which radio allows. For the "Grandma visits the table" shot, I had laid the flash on the floor behind the couple's table ... they always cram the Bridal table up against a wall, and if you use on-camera flash it can cast ugly shadows on the wall behind the subject ... the rear light solves that. For part of the reception, I just left one of the speed-lights on the Bridal table, and when I saw a pic to take, I switched to the transmitter channel for that light and fired it ... shown in the shot with the Bride eating cake ... I even back-lit the cake detail, which eliminates the hot spots and blown white cake frosting and silver stuff.
Cheers, and questions/clarifications welcome ...