The combination of film format, camera and lens are critical to the appearance of your image.

Some cameras especially those for general purpose photography may include two formats in the one camera normal and one panoramic.

The most important combination is that of format and lens.

Lenses are described in terms of their focal length so you may get a lens that is 15mm, 30mm, 50mm, 85mm, 200mm, 500mm or 1,000mm and beyond. Older lenses in some texts, before metrication, may be described in inches. An interesting site with information about Forensic photography is at http://www.fmap.archives.gla.ac.uk/.

However the effect on the image of these lenses is determined by the film format. For some camera film formats a 30mm lens is wide angle for others it is a standard lens.

This is especially significant to remember with digital cameras as the body may be derived from a standard 35mm format camera but the sensor in the camera is smaller the 35mm film, more equivalent to a half-frame camera.

So a 50mm lens on a 35mm format camera will be a standard lens but on a digital camera will be a portrait lens (equivalent to 50mm x 1.5)

Pythagoras' theorem - The square on the hypotenuse is equal to the sum of the squares on the other two sides.

Using this formula

The length of the diagonal = Square root of (35 x 35) + (24 x 24), multiplied out this = Square root of 1801, which = 42

So anything less than this is wide angle and greater is telephoto. The lens most commonlly seen as astandard lens is 50mm although used to also find 45mm as a standard lens. Many cameras now come with a zoom lens either a wide angle zoom or wide angle to telephoto.

This is especially important to remember with digital cameras as most have smaller CCDs than 35mm film so although the camera lenses fit digital and traditional cameras the lenses give different fields of view. This is often refered to as a difference of a factor of x1.5 so a 200mm lens on 35mm film will give you the equivalent of 300mm if you use it on a digital camera.

Zoom lenses and zoom ratios 

Zoom lens is a lens with a variable focal length e.g. a 28mm - 50mm lens is called a wide angle zoom.

The zoom ratio of a lens is the ratio of maximum to minimum focal lengths available. While ratios of 30:1 or 20:1 are common in film and television work, much more modest 2:1 or 5:1 ratios are used in still camera lenses.

Usually the focal length covers medium long focus to long focus or semi-wide angle to medium long focus.

Be careful about the difference between an optical zoom and a digital zoom. An optical zoom retains image quality but a digital zoom doesn't (The greater the zoom the poorer the quality).

Filed of view

As you change lens from 15mm to 30mm to 50mm to 80mm to 105mm from the same position all that changes is the field of view that is recorded. These photographs were taken with Fuji FinePix S3 so multiply focal lengths by 1.5 for 35mm equivalent.

The 15mm lens covers a wide area but there are two problems associated with this focal length what are they?