Off-camera vs On-camera flash
I recently got a flash that is compatible with my camera and will shoot ETTL mode. ETTL stands for "Evaluative-Through The Lens". For those of you reading who don't speak "lighting", this means that you can put the flash on your camera's hot shoe and forget it's up there. The camera will communicate with the unit and adjust everything as you adjust settings in your camera and as it sees things through the lens.
If you change your zoom, the flash zoom changes with you. If you close down your aperture, the flash reacts accordingly and knows to put out more power. All of this is done with no effort and without you doing any extra work than what you'd normally do if there were no flash present.
If you shoot in Automatic of "P" mode, you basically turn your DSLR into a point and shoot with a flash that is 10x more powerful than any point and shoot camera.
Having the flash on the camera, however, puts the light on the axis of the lens and typically produces a very flat looking image, as well as some hard shadows unless you have some lighting modifiers attached to soften the light.
98% of the time I do not have a flash on my camera. Primary reason being I don't typically like the way the light looks in an image with that kind of a lighting setup. The secondary reason is that, up until recently, I didn't own a flash that would let me shoot that way. I usually just rented one when I needed that ability - usually for a wedding I was shooting.
Since I got this flash that would do ETTL I thought I'd try it out on a shoot today. So I shot with the flash on the camera for the first time in well over a year (maybe even up to 2 years).
I thought I'd post a shot of what the results were so you can understand why it's usually more visually appealing to get the flash off the camera.
While the subjects are different and the rooms are not the same - meaning it probably isn't the best way to compare - you can clearly see in the off-camera one that the light is coming directly from the left side of the image. The light is filling the whole room and providing enough light to light the subject's face while providing a bit of lighting "drama" on one side for interest.
Whereas the on-camera photo is really pretty evenly lit across the entire image. The other thing that you'll notice is a slight green glow on the right of the face in the image shot with on-camera flash. This is because when the camera senses the flash on the hot shoe it immediately slows the shutter to 1/60th of a second, which in this case was enough to let some of the room light into the shot. The room was lit with fluorescent bulbs, which are tinted green. So that is another thing to take into consideration when shooting with the flash on top.
I'm still very much a fan of getting the light off the camera whenever possible, but I think I may start playing around with on-camera flash a bit more for speed and convenience when the lighting quality might not be quite as crucial to the shot. To get the light off the camera means setting up a light stand, and then you have to trigger said light at the same time as the camera shutter which means setting up wireless remotes. So instead of a 10 second motion of sliding a flash in place on the camera and locking it down, you're looking at additional setup time of around 2-3 minutes per light you want set up. Not a big deal, but when you think about moving around and shooting in different rooms, it means you also have to carry a light stand around, and sometimes fit it into awkward spaces.