So, photographically speaking, what is exposure? Sometimes we refer to a picture as an exposure, but that’s not what we’re talking about here. “Hey, Dana, my memory card only has enough room for a few more exposures!” No, that’s not what we’re talking about, today.
We want to discuss exposure as the process that occurs in the camera once we click the shutter button.
What Happens When We Press the Shutter?
When we push that shutter button, several things happen resulting in our picture being made. Our camera’s lens suddenly adjusts its opening (the aperture) to a particular size and the light passes through toward our camera’s sensor. The shutter, a light-tight barrier or curtain covering the sensor, then opens and exposes the sensor to the light for a particular period of time (the shutter speed) and then closes.
Now our camera sensor’s sensitivity to the light is adjustable through its ISO setting. The higher the particular ISO setting, the more sensitive the sensor will be and the less light will be required to create our photograph.
That’s the exposure process. Whew!
What Can We Control?
As photographers, we want to control and manipulate all the variables in that process because each of them can dramatically affect the way our photograph looks. So what are the variables again that we can control?
- The size of the lens aperture
- the shutter speed
- and the ISO.
They all work together. In fact, a number of photographers and photography teachers refer to their relationship as the “exposure triangle”. I think its a useful tool for understanding exposure. It looks like this:
If you change any one of these factors, it affects the other two and the overall exposure.
Another way to think about exposure is to liken it to a glass of water. The full glass of water is the exposure, and the water itself is the amount of light needed to make that exposure. So, you can fill a glass several ways …
- You can fill the glass by opening the faucet wide (the aperture) for a very brief period of time (the shutter speed); OR
- You can fill the glass by barely opening the faucet (aperture) for a much longer time period (shutter speed); OR
- You can affect the overall amount of water (light) needed by getting a larger or smaller glass (the ISO).
See how these three factors work together?
Why Not Just Let the Camera Worry About This Stuff?
That’s an awful lot to think about when I just want to take a photograph! Can’t I just set my camera on full-auto or program mode, and let my camera worry about it?
Well, of course you can. But then you’ve surrendered control over all the nuances of the photograph – depth of focus, sharpness, lightness, darkness, whether motion-filled scenes will appear frozen – or creatively blurred to convey the sense of motion.
There’s a wonderful world of creative images out there, and they can be your images! Just take a little time to understand how to manipulate aperture, shutter speed and ISO to control the image.
I really appreciate you being here! Please leave a message below with your questions or comments. I’d particularly like to know what you’re interested in reading on the Lens Lessons blog.
Now, go shoot.