Understanding Lens Multiplication with DSLRs

Most interchangeable lenses were originally created and rated for the 35 mm film plane of traditional SLRs. If you compare the area of a 35 mm film plane with the area of most digital image sensors’ image planes, you’ll see  that the area of most digital image sensors is a bit smaller. The focal length of a lens changes when it is put on a DSLR with a digital image sensor smaller than 35 mm. This smaller image plane effectively increases the focal length of the lens because more of the image circle coming out of the lens is cropped. For example, if you put a 100 mm lens on a DSLR that has a 24 mm digital image sensor, the focal length of the lens is multiplied by a factor of approximately 1.3. A 100 mm lens with a 1.3x multiplication factor effectively becomes a 130 mm lens (100 mm multiplied by 1.3). Another reason to take lens multiplication into account is that shooting wide-angle images becomes increasingly difficult when using cameras with smaller digital image sensors. For example, if your digital image sensor is 24 mm, you require a lens with a focal length less than 24 mm to achieve a wide-angle view. Check your camera specifications for the size of your digital image sensor.

Digital Point-and-Shoot

This is a lightweight digital camera, aptly named after the two steps required of the photographer to capture an image. Basically, point-and-shoot cameras require pointing the camera and taking the picture without manually adjusting settings such as the aperture, shutter speed, focus, and other settings that professional photographers routinely set on more sophisticated cameras.

Digital Single-Lens Reflex (DSLR)

This camera is named for the reflexing mirror that allows you to frame the image through the lens prior to capturing the image. As light passes through the DSLR camera’s lens, it falls onto a reflexing mirror and then passes through a prism to the viewfinder. The viewfinder image corresponds to the actual image area. When the picture is taken, the mirror reflexes, or moves up and out of the way, allowing the open shutter to expose the digital image sensor, which captures the image. Most features on a DSLR are adjustable, allowing for greater control over the captured image. Most DSLR cameras also allow the use of interchangeable lenses, meaning you can swap lenses of different  focal lengths on the same camera  body.
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