LENSES

Note: The information in this section refers mainly to the 35mm format.

As we have seen the normal lens is one that has a field of view that is similar to that of the human eye, about 46°, and is approximates to the diagonal dimension of the negative format, 43mm for 35mm format 90mm for a 6 x 6cm negative etc.

Note: Digital cameras are often quoted as having 'focal lengths equivalent to 35mm cameras' these lenses are usally of much shorter focal lengths than 35mm format lenses, but due to the smaller image area of the CCD chip, the field of view is similar to that of the 35mm negative.

Drawings Not to Scale.

The angle of view of a normal lens is approximately 46°, about 50mm focal length for 35mm format.
Photographs taken with a normal lens will have a 'natural' perspective, as seen by our eyes.
Objects in the scene will appear in the 'correct' proportions to each other.
The normal lens is ideal for general photography as it has a fair depth of field and can be focussed over a wide range from about 1metre (3ft) to infinity

Typical 50mm f1.4, Autofocus lens.

Manual focus, 50mm f1.2 lens.

The normal lens, is usually a fast lens,with a large maximum aperture, in the range of ƒ/1.2, ƒ/1.4 and ƒ/1.8, which allows you to take pictures in low light with reasonably fast shutter speeds. It is also a sharp lens that is easily-focused, with images that are free from distortion. They have excellent resolution and color rendition.Some have macro capability, making them useful for close up work.
Most good lenses will stop down to apertures as small as ƒ/22 which gives excellent depth of field.

The diagram, left, shows the depth of field for a typical 50mm lens at various apertures when focussed on a subject at 7 and 3metres.


Note how the DoF increases as the aperture gets smaller, and decreases as the point of focus gets nearer to the camera.

Conclusion.
Overall, the normal lens is a good general purpose lens, that can be used in many everyday situations, including landscapes, portraiture, low-light work and candid photography
It is also a good lens for general portraiture, although it will cause some slight distortion of facial features if used in extreme close-ups.