Project: Standard focal length

The standard lens is that which produces the ‘as seen’ image, having no distortion or lengthening / shortening of perspective, which one would think ideal for most journalistic or factual photography. Using this lens means that the photographer must move the camera to frame the image, instead of varying the focal length.

Langford’s Basic Photography tells us that the standard focal length for a 35 mm lens is around 50 mm. This is based on a film dimension of 24 x 36 mm. A DSLR (not full frame) has a sensor 15 x 22.4 mm. Because of this reduced target area, a focal length of around 28 mm is the standard lens for these cameras. Michael Freeman’s ‘Photographing People’ states that technically the standard focal length is the same as the diagonal across the array, which equates to 27 mm for the above sensor. This is not strictly true, because sensor sizes have increased since this book was published (2010) and other factors (e.g. crop factor) affect the calculation.

The Photography Mad website: http://www.photographymad.com/pages/view/standard-lenses gives a good overview of the ‘standard’ lens:

“A standard lens, also known as a "normal lens", is one which produces an image that roughly matches what the human eye sees, and which looks natural to the viewer. It sits between the telephoto lens and the wide angle lens, which produce unnaturally zoomed-in and zoomed-out images respectively.

Standard lenses have an angle of view of around 50 to 55 degrees diagonally. This is roughly the same as the angle that the human eye can comfortably view, which is why it gives a natural-looking perspective.

Normal lenses make great general-purpose lenses, and can be used to photograph everything from close-up portraits to landscapes. They tend to be very "fast" lenses (i.e. they have a wide aperture), making them great for indoor and low-light photography.

The technical definition of a standard lens is one whose focal length roughly matches the diagonal or the film or image sensor. For a standard full-frame 35mm camera this gives a focal length of around 43mm.

In reality, the actual focal lengths chosen by manufacturers tend to be slightly longer than this. For a 35mm sensor, 50mm is the most common standard lens, although some companies do sell lenses which are closer to 43mm focal length.

Crop Factor

Because the "ideal" focal length depends on the sensor size, cameras which are less than full-frame will require lenses with shorter focal lengths. For example, a camera with a 1.5x "crop factor" will require a lens which is 1.5 times shorter than the standard 50mm, which works out at 33mm. A number of manufacturers produce 35mm standard lenses to meet this requirement.

Perspective

By definition, a standard lens produces images whose perspective is very similar to that seen by the human eye. This gives their photos a pleasing, natural feel, and helps focus attention on the subject, rather than distracting the viewer with an unusually distorted image.

Because of their ability to accurately reproduce a scene, standard lenses are an excellent choice for photographing people. They are particularly good when shooting candid photos, where you want to include some surrounding scenery to put the subject in context.”

With this in mind I’ll use a standard lens while photographing for the ‘Public event’ exercise. The images for next two exercises were captured at the same time and venue using two cameras. Both cameras were hand held as a tripod would have been impractical in a crowd and I was also trying not to be noticed.