Sensor Size, Crop Factor and White Balance

Sensor Size and Crop Factor

This isn't critical information to know, but it is good to have an understanding of it. The 35mm cameras are based on the size of the film used in the cameras. This fact is included in determining the focal length of the lenses. So a 100mm lens is designed for a 35mm camera.

Today's DSLR's usually don't have 35mm sensors. They are usually smaller. Canon does have a couple of cameras that have "full frame" (35mm) sensors, but they aren't cheap. The least expensive one sells for around $2,500 right now.

Most DSLR's have smaller sensors with a crop factor of 1.5 (Nikon) or 1.6 (Canon). That means that if you have a 100mm Canon lens on a Rebel with a 1.6 crop factor, you will get the equivalent magnification of a 160mm lens. Just take your focal length and multiply by 1.6 (or 1.5).

Having a seemingly longer focal length isn't necessarily great. If you were to take an image from a full frame camera you could crop it down in size to get the equivalent picture. With a full frame camera you get more picture to work with. I use a full frame camera, and I wouldn't want to use anything else.

This crop factor can impact your depth of field. When filling the frame in both the full frame and 1.6 crop factor camera you will get less depth of field (more out of focus blur) with the full frame camera. This makes much better portraits.

White Balance

The color of light varies with different light sources. Have you ever taken a picture indoors and get an image with a brownish orange cast to it? That is because the color of the tungsten lights lighting the room is that color, and your camera didn't adjust properly.

Fluorescent lighting and light from the blue sky tend to be bluish. When clouds cover up the blue sky it changes the color again. If your subject is laying in the grass you will tend to get a green tone added. Our eyes easily compensate for this, but our cameras need a little help.

There are probably different settings on your camera to set the white balance. You can often use the auto white balance and be OK. For some cameras it may not work as well. You can also set it to your specific need like daylight, tungsten, shade, cloudy, etc.

Note: If you shoot JPEG's you really need to get the white balance right in the camera. But you can be a bit more flexible by shooting RAW.