Kaitlin Hansen Photography

Exposure – How aperture and shutter speed effect it.

Exposure refers to the amount of light that is allowed to hit the photographic medium in use. Before digital cameras, that was film.

Aperture is primarily used to change the depth of field, (as discussed in “D”) and shutter speed is used to blur or freeze motion (which will be discussed in “S” week).

However, aperture is also a measure of how wide the lens opens when you take a photo. Shutter speed it how long the shutter stays open while taking a picture. Both of these setting affect the amount of light hitting hte camera’s image sensor, and this is what determines exposure.

When the correct amount of light hits the image sensor of your camera, you get a photograph that is correctly exposed. When there is not enough light, the image is underexposed. Finally when there is too much light, the image is overexposed.

If you recall, back in “a” week we discussed the relationship of light and aperture. Large f number means small light and vice versa. So if you have your aperture set to a small number (ignoring the shutter speed right now) you are letting a lot of light into the camera. As you can see, when you are shooting in low light situations, like at dusk, or inside, you probably will need to have your aperture wide open.

We’ve covered aperture enough over the weeks, you should have the hang by now. So I am going to move onto the relation of light and shutter speed.

Slow Shutter Speed= Large amount of light

Fast Shutter Speed= Small amount of light

Let’s say you are only adjusting the shutter speed and ignoring the aperture. In low-light conditions, you will have to use a slower shutter speed to capture enough light for good exposure. In bright conditions, you can use a range of shutter speeds, but may not be able to use slow shutter speeds since this will let in too much light.

Between Shutter Speed and Aperture you can manipulate both to make sure you have the correct exposure!

{Overexposed=a slow shutter speed and a small f-stop will both let in more light}

{Correct=a fast shutter speed lets in less light, but a small f-stop lets in more}

{Correct=a slow shutter speed lets in more light, but a large f-stop lets in less}

{Underexposed=a fast shutter speed and large f-stop both let in less light}

Here some quick examples of exposure:
Underexposure:

Correct Exposure (or close to):

While this may look underexposed, it was infact taken on an overcast day. The spots of gray and black give depth, and help me know I am near good exposure. You don’t want an image to be white washed and loose that sense of depth (unless that is what you are going for).