What is Off Camera Flash?
The general idea is that you find a way of syncing you camera with your flash so that you can take it off of your camera and illuminate your subject for a different angle. You'll need a separate, off camera flash, but there's plenty of choice to suit your budget and needs. When you take your flash off your camera, you open up a whole load of different options when it comes to diffusing the light through various umbrellas, softboxes and beauty dishes.
Why you Should use it
It's not the flash that you use that's important, it's where you put it. I'm a strong believer in this as it allows you to be able to disguise the light from being a very obvious, flat light to much more subtle and natural looking. The biggest difference this makes is the appearance of depth that this produces, because, as we all know, when you fire the flash at the same angle as your lens, you flatten all the natural shadows. When you have your flash off your camera, you can move it into a position where it only lighten the areas which you want to be lit.
What you'll Need
Of course, you're going to need an external flash unit, preferably one that is made to go with your camera as you'll have more control over the flash when it's off the camera. You have 4 main options for syncing your camera with the off flash and they're listed below in order of cost.
- PC Sync Cable - Link to Buy
This is by far the cheapest option and you'll find it's pretty easy to set up. You'll need a flash with a PC sync cable port to make this work (some entry level cameras don't have these) and a flash that you can plug it into. Old flashes and high end flashes will have sync ports, but you may find that mid range flashes such as the Canon Speedlite 430EX II
- Off-Camera Shoe Cord - Link to Buy
This is similar to the one above, only more sophisticated, with the ability to share more information though the cord. It's a popular choice and it's becoming increasingly popular amongst pros because of their ability to cary metering information down the cord to the flash. This is something that's not possible with a radio transmitter and although IR transmitters can do this, their signal between transmitter and receiver can prove to be somewhat unreliable at times, which is not what you need when you're a pro.
- Infrared Transmitter - Link to Buy
This is what I currently use as it requires the least amount of gear and does what I need it to do. It does the same job as the cord above, only it does it wirelessly and the transmitter also fires an assist beam which helps massively to focus in the dark. This is a pretty clever way of creating wireless flash over short distances, but it does requires the IR beam to be able to see the flash. A lot of modern cameras and flashes are building transmitters in to their hardware so this is becoming quite a popular choice.
- Radio Transceiver - Link to Buy
This is what a lot of professional photographers use as their workhorse gear as it's easy to set up and reliable for long distances and long periods of time. Because it uses radio waves, the flash and camera don't need to be able to see each other which means that 
chnology, but Pocket Wizard seem to be the most popular.
- Bonus – Slave - Link to Buy
This is a real budget way of creating an off camera flash as the slave picks up when another flash of light has been set off and sets theirs off directly after. You're never going to get quite the same effect as you need to set your on camera flash off to make this work, but it's a good option for firing off 2 flashes when 1 is already on a sync cord.
Uses
Well, now that you know how to set it up properly, it's just a case of trial and error until you find a lighting position that suits your style or whatever you're shooting. Here's a few ways that I like to use it to improve my photography.
Fill Light
I've actually written a whole blog post on fill flash, but the basic concept of it is to fill in the areas that the camera can't capture as well, perhaps due to another dominent light in the frame. In my photo below, there was a very strong light coming into my camera from the sun, and because I didn't want the side of my model to be underexposed, I used a flash to fill in the light. It works really well and very evenly exposes her skin.
Room Light
I often do this when shooting inside where it's a little bit darker; I set up a one or more diffused flashes and fire them at the ceiling. This produces more light for me to work with and is even across the skin of my models. I had two flashes set up for the photo below, one either side of the model, and this produced a really soft effect, without appearing to be obviously flash photography.
Disguised Flash
I often like to use the flash to illuminate the subject without the viewer realising what I'm doing so I'll place the flashes somewhere that makes it seem as if it could have come from the subject's surroundings. In my photo below, I wanted to capture my subject with the light coming from an angle because his face was at an angle too, so I moved the flash to the left and above. This made it look like the light could have come from external house lights in the garden we were in.
Obvious Flash Separation
I don't always want to hide the fact that a light was used, in fact, sometime I like to make sure the viewer knows it was used. In my photo below, the angle and lighting made it stand out from the ambient light in the scene which forces the viewers attention towards the subject, which is exactly what I wanted. These are all things to consider when doing flash photography – where do you want your viewer to look and how can you make them look there?
Set Lighting
Often when the lighting is good on my model, I like to use a flash to light up a part of the set that they're standing in. This works particularly well on the rocks below as the harsh light contrasts on the rocks, which in turn contrasts the the soft skin of my model. Using a light to illuminate part of the set can be a lot of fun to play around with and create an interesting background. With a little playing around with the photo below, I was able to position my flash so that it didn't cast any nasty shadows on my model, by getting her to hold it between her feet.
What to Watch out for
The biggest thing you'll notice when adjusting your flash placement is that you need to be careful of the shadows that you cast. If you set the flash up 90° to the subjects face and set it off then you're always going to cast a harsh and unnatural shadow from the side of the nose, across the cheek.
Good article! I use a small LED light to determine ahead of time where to position the flash and see roughly what the end result will be. Saves taking lots of shots to get it right.