Angles of View and Crop Factors

// February 5th, 2010 // Photography

Here are some more diagrams I drew to try and understand photography, specifically to understand crop factors and lens lengths.

Sensor Crop Factors

Every camera has a rectangular sensor which captures light. A “full frame” sensor is the same size as an old film negative – 35mm from bottom left to top right corner. Expensive SLRs use full frame sensors, but cheaper ones (such as any Canon in the x0D, xx0D and x000D ranges) use smaller sensors. The size of the sensor is described as its crop factor.

This diagram demonstrates the common crop factors found in digital SLRs (click to enlarge):

This explains why a larger crop factor will reduce vignetting (the darkening around the corners of a photo):

Note that we are talking here about conventional lenses designed for full frame cameras. Most manufacturers now also produce lenses which only work on crop factor sensors, such as Canon’s EF-S lens. These project a circle which does not reach the edge of a full frame sensor; understandably, these will vignette worse than the equivalent length lens designed for a full frame sensor.

Camera Lens Angles of View

The focal length of a lens is the number, quoted in mm, which indicates how close or far away things will look through it. This can be considered as an ‘angle of view’ – a larger focal length will produce a smaller angle of view – and a closer image. Think of it as the angle from the lens to the left edge across to the right edge of the frame.

Angles of view for a “full frame” sensor (click to enlarge):

In contrast, here are the angles of view for a 1.6x crop sensor:

For easier comparison, here they are side by side:

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