Lenses for Cropped Sensors

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Today’s Question: I see some lenses being promoted as having been designed for cameras with “cropped” sensors, often to provide a wider field of view. But can these lenses still be used with a full-frame camera?

Tim’s Quick Answer: No, lenses that are designed for cameras with “cropped” sensors can’t really be used on full-frame cameras, since the image circle projected by these lenses is not large enough for a full-sized sensor.

More Detail: Lenses in general are obviously designed for a specific camera system, which generally just means a lens will be compatible with the mount for that camera. So a lens might be designed to mount onto a Canon versus Nikon digital SLR, for example, or for a specific mirrorless camera system mount.

With some camera systems, however, different bodies might use the same lens mount but have different sensor sizes. A common example would be various digital SLR cameras that essentially evolved from 35mm film cameras. Some of these digital SLRs have a sensor that is the same size as a frame of 35mm film, which are generally referred to as “full frame” models. Others have a smaller sensor, which are often referred to as having “cropped” sensors because the smaller sensor is cropping a smaller area of the image circle.

Because a “cropped” sensor is capturing a smaller area of the image circle projected by the lens compared to a full-frame sensor, the photos captured with a cropped sensor have a narrower field of view than the same lens would have provided on a full-frame camera. For example, a 100mm lens on a camera with a 1.6X cropping factor due to a smaller sensor would provide a field of view equivalent to a 160mm lens on a full-frame camera.

So, cropped sensors enable our long lenses to provide the field of view of a longer lens. But those sensors also mean you are missing out on the capabilities of a wide-angle lens. For example, a 16mm wide-angle lens on a cropped sensor camera might give you the field of view comparable to a lens with about a 26mm focal length. That can be a big shortcoming.

To compensate for this issue, many lens manufacturers have started designing lenses specifically for cropped sensors. For example, a 10-24mm lens would make up for the loss of wide-angle capabilities, providing an effective range of 16mm to 38mm compared to a full-frame setup.

However, these specialty lenses project an image circle that is smaller than a “normal” lens designed for a full-frame sensor. That means if you used such a lens on a full-frame camera, the edges of the photo would be dark (as in basically black) because the image circle would not cover the full size of the sensor. Therefore, it is important to be aware of not only the lens mount a lens is compatible with, but also the sensor size that is supported.