what is crop factor
(focal length multiplier)

Understand the terms crop factor and full size sensor will help you when you are considering options on buying or using different lens and camera combinations.

Illustration comparing different crop factors

Before the advent of digital cameras and digital sensors, camera and lens manufactures made their cameras to work with 35mm film. It was the most popular and most widely used format in photography for many years.

It was easy to compare different camera lenses, their focal lengths and their zoom ranges. A 50 mm lens was considered "normal" and longer lens were considered telephoto. Shorter lenses were considered to be wide-angle.

Now digital cameras can be made without a full size sensor (a sensor that is the same size as a 35 mm film "negative.")

The illustration above show you what would happen if you used the same lens on cameras having smaller than full frame sensors. A "crop factor" means that your photograph would have a smaller field of view. In other words, it crops part of the photograph that the lens is capable of including in your photo.

As a result – when you fit a lens to a camera with a smaller sensor the lens is often said to have a larger equivalent lens size.

crop factor chart

The chart below shows you how a certain lens "acts" when it's on a crop factor camera.

See what the effect is on this Crop factor - lens conversion chart

Look at the 2 highlighted spots in the chart above. Using a 50 mm lens on a camera with a full size sensor would give you the same effect of using an 80 mm lens when using that same lens on a camera with a 1.6 factor sensor.

That lens would be "normal" on a full size sensor camera and would be a telephoto lens on the camera with the smaller sensor. To see examples of this, take a quick peak at the photos in this article on lens comparison: Camera Lens Comparison

It is easy to erroneously think in our minds as photographers that putting a certain lens on a smaller crop sensor gives it extra zooming power.  One of the big considerations in choosing a camera based on sensor size that many can easily ignore is depth of field.

Depth of field in photography is greater with smaller sensor cameras.  In cell phone cameras for instance, the physical dimensions of the sensors are so small that they inherently have a very large range of things in focus compared to a full-sized sensor camera.

Camera buying advice.  A guide to help you chose the right camera. Don't get fooled by the megapixel myth.

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