Aperture

Aperture

The second variable of flash exposure is Aperture.

The aperture setting is going to control two things, your flash exposure and your available light exposure. This is one of the variables that controls both exposures equally. When you open your aperture you are allowing more light into the camera. You can think of the aperture setting like a funnel. The larger the hole is at the bottom of the funnel the more water can pour in at a given time. The smaller the hole in the funnel, the less water. Same thing for your aperture. The wider your aperture setting is, the more light is going to come into the camera at one time, the smaller your aperture is, the less light will come into your camera at one time.

Your aperture setting is measured in stops, just like with shutter speed! This is very important to memorize as it will help you adjust your settings easier and faster. In the illustration above you can see the different settings for one stop adjustments! A quick way to remember it is that if you double or halve the Aperture setting you are at, you adjust by two stops. So if I'm at F/8 and I need to open up my aperture because my image is underexposed by two stops, I would go to F/4. If I had to close down my aperture by two stops because my image was over exposed I would go to F/16. It can get a little confusing because unlike shutter speed every time you halve or multiply you are actually adjusting by TWO stops instead of ONE in Shutter speed! The only way is to memorize, so don't give up!

Moving on, since the aperture is just a hole that regulates the amount of all light that enters the camera at a given time, it can not distinguish between available light and flash light. To the aperture setting they are both equal, hence affecting both exposures equally. When you open your aperture one stop, you allow one stop of available light in, as well as one stop of flash light in. Same is true when you close your aperture, you allow less of both types of light into your camera.

Your aperture setting is also going to control another important aspect of your photography, your depth of field. The depth of field is how much depth of focus your photograph will have. The wider the aperture, the less depth of field you will have. The smaller the aperture the more depth of field you will have. This is something to think about, but I will go into more detail of this later, just keep this in the back of your head for now.

The aperture setting is extremely important in flash photography because of something called Max Sync Speed. Max Sync Speed is directly related to shutter speed. This is the maximum shutter speed that your camera will allow the flash to sync with it's curtains. Most camera's have a Max Sync Speed of 1/250th of a second. That means that any shutter speed above 1/250th of a second will cause a black bar in your photograph. This black bar is caused by the second curtain closing before the flash has had a chance to fire. This Max Sync speed causes a limitation in controlling your Available light. Remember that your shutter speed only controls your available light. If you are shooting in bright available light conditions your shutter speed will be maxed out at 1/250th. In bright conditions, 1/250th of a second shutter speed is not enough and your available light will still be overexposed, so this is where Aperture comes into play. The more you close down your aperture, the less available light will come into your camera and you will be able to control your available light exposure.

The important thing to remember is that every time you adjust your aperture you are affecting both your available light exposure and your flash exposure.