Exposure Quick-Tip

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One of the most frequently asked questions I hear from new photographers moving from a point and shoot to the world of dSLR cameras is related to exposure. How do you properly expose a photography?

Proper exposure is one of, if not ‘the’, key component to producing an attractive and interesting photograph. There are techniques and effects where you will want to purposely under or over expose a photo, but in general terms the proper exposure of photography is a key element.

To discuss exposure, we should probably start with its basic definition. Exposure is basically the total mount of light that falls on the image sensor (or film) during the process of taking a photograph. In today’s digital imaging world, you will often see the value displayed in terms of exposure value (EV).

There are three primary components of how you achieve the correct EV:

1. ISO
2. Aperture
3. Shutter Speed

ISO use to be referred to as ASA n the film days, but today we use the ISO equivalent when discussing digital photography.  In general terms, ISO is how sensitive an image sensor in the camera is to the amount of light present. The higher the ISO, the more sensitive to light the image sensor is and will allow you to take a picture in low-light situations. However, the downside to using a high ISO value is that it can introduce “noise” into the image.

Aperture is related to the lens you are using on the camera. The aperture of the lens is the diameter of the opening on the lens. The larger the diameter of the aperture is, the more light reaches the image sensor. Aperture is expresses in F-Stops such as F2.8 or f/2.8. The smaller the F-Stop number (f/value), the larger the lens opening (aperture) is.

The final component of proper exposure is the shutter speed. The shutter speed is the amount of time that the shutter is open during the actual taking of the photograph. You will see this time expressed as fractions of a second such as 1/1000 is one one-thousandth of a second.

Each of these elements plays a part in the exposure process. Instead of trying to reinvent the wheel here, I’m going to use the metaphor that I’ve found is the best way to understand exposure. The following explanation was taken from Matthew Coles site.

Fill That Bucket!

My favorite analogy for exposure is filling a bucket with water. A bucket is of fixed size and needs a certain amount of water to fill it, just like film or a digital sensor, which is of a set sensitivity (the ISO) and needs a certain amount of light to optimally capture an image. To fill your bucket, you can pour a small stream of water for a long time or a fast stream of water for a short time. Either way, you end up with the same amount of water. In photography, the size of the stream of the water is analogous to the f/stop, the length of time you pour is analogous to the shutter speed, and the size of the bucket is analogous to the film speed. Broadly speaking, from the bucket’s point of view, it doesn’t matter which combination of stream size and length of time you choose as long as the right amount of water ends up coming in.

I hope you found this Quick-Tip helpful!

Until next time…