Light is something that is Relative

Posted on December 17, 2012


As a photographer, you need to understand that light is relative. It’s that simple. Wait? What do you mean simple? What do you mean wait?

A lot of photographers spend a lot of time figuring out that light is relative. I am embarrassed at the number of photographers who think you need multiple high power studio lights to “overpower” the sun. Well… Can you shoot at F16 or smaller aperture (larger number) at the inverse of the ISO for shutter speed with your flash? Of course you can. It won’t be very flattering in most cases, but you can do it.

You have heard me refer to “layering” light in previous posts. This is a technique where you work with each strobe (or flash) you use to create one point of light in your image with exactly one light. Keep in mind that if you are outside or dealing with natural sun light, ambient light is one of those sources of light.  You can control all of them through various methods that include shutter speed and aperture.

The first thing we want to set is our ambient light or fill light – if any. That is fairly easy to do through the camera’s own metering. But, this is where it gets tricky – say you want to make it darker or lighter than a ‘normal’ exposure? Easy, just adjust the exposure, right? Exactly.

Let us add a person in the image as a subject who should be about 1 to 1.5 times brighter than the background. This means adding a strobe of some kind. We find out what the background is set and adjust another light source so that it is 1 to 1.6 times brighter. We can do this with a meter or we can do it with the back of the camera (just know if we chimp this stage, the display on the back isn’t calibrated, so you will have to do additional adjustments in post that could be complicated if you do ).  You now have two layers – the background and the flash that illuminates the subject.

Simple. Right? But what?

Ok, let me explain this a little further for those who want to tinker with this and learn something. The shutter speed on the camera adjusts the exposure, but it adjusts only the ambient light – not the flash. The slower you set the shutter, more of the background starts to appear in your image. The faster you set it, less of the background will appear illuminated. If you use high speed sync and set it to something like a 300th of a second, the background is probably all black if not lit up by a flash. Set it to a 15th of a second, and the background is completely visible. Setting the shutter to this slow of a speed (or slower) is called “dragging the shutter”. It is one of the neat techniques us photographers use when using a strobe.

Warning: be careful when you drag your shutter that you are steady at that slower speed and don’t shake the camera, or be sure to use a tripod to hold the camera steady. If you don’t, the image will be blurry and not sharp. Also be aware that any person shot at less than 1/30 of a second will probably be blurred somewhere as most people have a difficult time staying completely still.

So, how do we adjust the flash amount on the camera? This is a combination of both the aperture and flash power. I try to set mine at 1/4 power to start and 10ft away – for my flash, that is F11. Double the power on the flash to 1/2, keep the distance the same, and the aperture becomes F16. Simple, right? How do I know this? I went and checked this out with my flash at night. It is an easy test to do – just take a flash, your camera, and a tape measure. It also helps to take your flash off your camera.

So, now we have the flash to the background set and the subject flash set. If you want more lights in the image, then work through them by just adjusting their power. This is easy to do. Again, you should have a base power level and distance for all your flashes for a specific aperture level. Start at that base level adjusted for the aperture you already have set. If you have a flash meter, you may want to meter all the flashes going off at once and double check your lighting settings don’t go over that value.

This should give you an idea of how to set up multiple flashes by layering your lights. Keep in mind that the lights should only light one thing in your image – and that they shouldn’t overlap with the light they provide unless you want a shadow from that light. This should also give you a starting point for multiple lighting setups that you see in books and online.