External Flash basics

On Saturday, I got out to Point Pleasant with some photographers from the Sackville Photography Club to do some work with external flashes.  It was a blast! I hope everyone that came out enjoyed the day as much as I did.  We got through a lot of stuff and had a chance to test out some basic techniques while we were out.

Let's jump right into the topics we covered:

Making the best of on-camera flash.   

The limitations of having the flash on the camera are pretty numerous, but sometimes you just need a bit of extra light to help your subject pop.  If you can't get the flash off the camera, there are a few ways to make the best of the light you have.

  1. Bounce the flash if possible.  The ideal situation would be finding a white wall or ceiling to bounce the light of your flash off to help soften it.  The results are usually much more flattering than pointing the flash bulb right at a person or object.  If you don't have a wall to bounce off, a piece of white foam core or a collapsible reflector can be a makeshift wall.
  2. Increase the size of the light source.  This can be done with small softboxes that go right on the camera's flash or a small bounce card.  These little light modifiers help to diffuse the light the same way a wall does, but the source will still be small
  3. Use a bounce cap, point it at the person and dial the power back as much as you can to fill in shadows.  I use this technique to help fill in shadows under a ball cap for instance, or to add a little bit of light into a scene.  

Keep in mind that the direction of light plays a very crucial role in flash photography.  With a hotshoe flash pointed forward on your camera, the light direction is going to provide you with slightly flat results.  In this situation,  it's especially important not to overdo your flash intensity if you're trying to make the photo seem natural.

Here's an example of too much flash.  I was letting the background get quite dark, so the flash was compensating and lighting up Lloyd the best way it knows how.  You usually see this kind of lighting from a compact camera at someone's party.

This is a more balanced image.  I let the flash fill in the shadows, but also allowed lots of ambient light to come through. The result is more pleasing, and not nearly as flat. 

Flash sync speed

Your flash and camera are highly technical pieces of equipment.  They operate at such high speeds that our eye can barely register them.   The simple explanation is that the length of time that the flash is activated has to fit within the length of time that the shutter is open.   For technical reasons, most cameras have a "Flash Sync Speed" which limits the shutter speed that is possible to use effectively with flash.  This is what happens when we don't adhere to the rules:

Natural light is kinda dark, I want to add some flash

oops, my shutter speed is too fast, and now I've got this dark band.  If I'd used a faster shutter speed, the entire image would be dark, as the flash wouldn't be exposed to the shutter at all.
Luckily, as long as your camera is connected to the flash on the hotshoe or with an off-camera cord, the camera won't let you push your shutter speed past the maximum sync speed. At least, not without engaging the High Speed Sync mode.

High speed sync

By putting your flash into High Speed Sync mode, you can use higher shutter speeds (please note that this is only available when you have communications to the flash that support this mode, such as an off-camera flash cable or wireless trigger designed for this purpose).  This mode can really help if you need to freeze action or darken down a scene on a bright sunny day.  The trade-off is that the intensity of the light from your flash is lowered somewhat.

Off Camera Flash

So, let's say you have a sync cord/flash cable and you want to start trying some off camera flash work.  Keep in mind that light direction is very important in making a good photograph.   When someone is lit from below, for instance, you can get that campfire lighting look (think horror stories with a flashlight).  I'm exaggerating a little, of course, but the simple solution is this: put your light where the sun would be.

Bare Flash, off camera left.  The flash is too low, as you notice the shadow from Lloyd's nose going upward.
These shadows look much more natural.  The light source is still harsh, but at least  the direction looks pretty good.

As you can see the light isn't superb, and it's pretty obvious that there's a flash in the scene.  The small light is going to give out harsh shadows and highlight areas that I don't necessarily want highlighted.  If I make the light source a bit more diffused by adding a bounce cap (omni-bounce or similar) I get the following result:

The light source doesn't have as many bad shadows, but it's also weaker.  This is pretty balanced though, and if I didn't have another modifier I'd be pretty happy with this shot.
Making the light source bigger helps to even out the shadows further, with the added effect of filling some extra light into the area underneath the brim of Lloyd's hat.  I used a reflective umbrella to get the following:

This light is much more even and as an added bonus, there is a catchlight in the eyes!

Finally, adding a reflector if you have one can fill in some more shadows, but a single light setup is actually pretty effective in this cloudy-day situation.

This was the final image, including a reflector off camera right. 
All of the above images were taken with the same shutter speed, ISO and aperture, so that you get a good sense of how the modifiers vary in intensity.  

Balancing ambient light and Flash

For the most part, our cameras will handle the flash intensity automatically using a method called "through the lens" (TTL or ETTL depending on the camera).  We can also control it manually by specifying the light intensity as a fraction of the maximum flash output.  The trick is to make the output of the flash balance the existing light as best as possible, and then tweak it with camera settings.

Here's the simple explanation:
Shutter speed controls your ambient light intensity.  If you want the stuff you're not lighting to be darker, use a shorter shutter speed.
Aperture controls your whole exposure, flash included.
ISO also controls the entire exposure.

Alternatives to flash

It goes without saying that flash is pretty handy, but what if you don't have one, or you haven't got a way of using it off your camera?  You can set up a reflector, which will help bounce light around the way we want it to.   They really work well, as you can control the light intensity using the distance between the reflector and your subject.  There are no headaches with sync speed, and you can see what your light will be right in the viewfinder.

Using a reflector to bounce some of that warm sunlight back into the scene

Further reading:
Please feel free to check out David Hobby's blog at http://strobist.blogspot.com/ for some really great lighting discussions.  His Lighting 101 entries are absolutely brilliant and have been a wonderful learning tool for me.