So the exposure triangle, the foundation of what I teach my beginner students. It is a simple way to explain the camera basics. What happens when you try to introduce the most important photography kit of all into the equation, namely lights? Well, the triangle no longer properly applies, and the exposure triangle becomes a square! A lot of photographers get completely lost when external lights are introduced because they change the rules they need to apply. When you introduce lights under your control you need to think about the strength or power of the lights and the ambient lighting in the scene you are in.
Here is a cool lighting example I like to teach first because it looks like magic to the uninitiated. These two pictures are taken seconds apart, thanks to Paul for modelling!
The only thing different in both pictures is the shutter speed and the flash power, let me explain how to do this as best I can here, though this is definitely best learned in practice instead! In picture one, I set my lens aperture ISO and shutter speed to get a decent exposure on the backdrop before I even turned on my flash. Once I had my backdrop the way I wanted it I then turned on the flash (inside an octobox to the side) and allowed the TTL (through the lens) connected to the camera to set the power. Note that this can be done with a manual flash too, it just requires more tinkering with the flash power initially. So I manually chose the exposure for the backdrop and the flash automatically balanced the flash on Paul's face to get a good exposure.
In picture two I estimated how bright the scene was turned, off the flash and set my shutter much higher, too high in fact. I was trying to "mess up" the exposure on purpose. This only really works in manual mode because in any other mode the camera will try to "fix" your mistake, namely too dark an exposure. Remember you are in charge of your pictures, I teach students how to use manual mode if they wish because a lot of cool photography techniques are not possible without using it. At the "too high shutter speed" the background ambient lighting was not strong enough or I was too far away for it to be strong enough to be captured by the camera. However, the flash isn’t actually affected by the shutter speed. The flash duration or pop is so fast that the only thing that affects its exposure is the aperture. So even though I left controlling the flash power to the TTL connection it likely didn’t change at all.
The result is that the background ambient exposure is wrong, in this case completely black but the exposure on the subject’s face, provided by the flash is perfect, the TTL connection sees to that. This gives the apparent look of a black studio background! Looks like magic right, well if you are new to flash it is but if you are experienced you will realise this is just one of the many cool effects you can achieve with a solid understanding of off-camera lighting.
This example was taken in a dirty mechanics garage, see the dirty wall at the bottom? the whole wall was like this but it is overexposed by the second flash pointed at the dirty white wall so looks clean white. That is a story for another time, get one flash mastered first before you even think about introducing another one! Need help with this stuff? Get in touch.
