Large Format Lenses
This page will help you choose the right lens for any type of photography you do. Before you decide on a focal length, you need to know a few things about large format lenses, as they are different from 35mm and medium format lenses.
Image Circle
The image circle is the size of circular image projected by lenses. This circle is large enough to cover the whole area of the film. The lens must have enough coverage to cover the whole area of film in order to prevent vignetting, or darkening of the corners of the frame. Unlike 35mm and medium format cameras which have lenses specifically designed for them with adequate coverage, large format cameras may require lenses to cover 4X5, 5X7, or 8X10 film sizes. Therefore, you must find out if certain lenses have enough coverage for the sheet size you intend to use. Different lenses might be required to cover 4X5 and 8X10 film sizes. Smaller film formats don't have enough coverage for larger films, for instance, a lens designed to give enough coverage for 4X5 format, do not have enough coverage for 5X7 or 8X10 formats, and cause vignetting. On the other hand, using a lens from a larger format such as 8X10 can be used on smaller formats, because it provides more coverage than the smaller format requires. Before purchasing a lens, check the specifications to find out about the lens' angle of coverage and image circle. This is usually given with the lens set at f-16 or f-22 with the lens focused at infinity. This will indicate whether a lens has enough covering power or not to project an image.
Angle of Coverage
Angle of coverage which is different from angle of view, is the measure of the entire image circle and refers to the image-forming cone of lenses or the area that produces sharp images. The size of the image circle depends on the specific lens design and tends to be similar for a number of different focal lengths. Several lens group from a series made by a manufacturer can have same angle of coverage. For instance, lenses from 75mm to 150mm group may have coverage of 100 degrees. Each format requires a minimum angle of coverage. 4X5 needs 161, and 8X10 requires twice that or 323. These are minimum requirements as long as lens axis is aligned with the center of the film. This is always the same with 35mm or medium format cameras, but not view cameras. View cameras allow several movements that the lens is moved off-axis from the center other film plane. When the lens is moved off-axis, a larger circle is need to cover the film. A lens therefore, requires a an image circle larger than minimum to cover the film area to allow camera movement.
Focal Length
Standard lenses (also called normal lens) simply means a lens that is neither a wide-angle or telephoto. The standard lens has an angle of view close to human eye. This is different from each format and is measured by the diagonal of the film size. 150mm lens is considered standard for 4X5 format, but 300mm is the standard for 8X10 cameras. Anything shorter then standard is called wide-angle and anything longer is considered a telephoto. The choice of focal length depends on the photographer and the type of photography he or she plans on doing. Longer focal lengths require more bellows extension to focus. The same extension as the lens focal length is need to focus at infinity, except for certain telephoto designs.
Leaf Shutters and Types
Large format cameras do not have built-in shutters. Leaf shutters of different types are used inside of lenses. Mechanical shutters are one of the types which are operated mechanically. With this type of shutters, first the shutter release is set and then a lever is pressed to open the shutter leaves to allow the photographer to check focus. Photographer must then close the shutter and press the shutter release to take the picture. Another type of shutter is the electronic shutter. The operation is the same as mechanical shutter, except the shutter speed is controlled electronically. Electronic shutters also have longer shutter speeds than one second. Leaf shutters come in different sizes to fit lenses of all sizes and are determined by the maximum diameter of the shutter. Currently shutters are available in the following types.
| Type | Size | Shutter Speed | Screw Thread | Lensboard |
| Copal 0 | 0 | B,T, 1-1/500sec | 32.5X0.5mm | 34.8mm |
| Copal 1 | 1 | B,T, 1-1/500sec | 39X0.75mm | 41.8mm |
| Copal 3 | 3 | B,T, 1-1/200sec | 62X0.75mm | 65.3mm |
| Compur 0 | 0 | B, 1-1/500sec | 32.5X0.5mm | 34.8mm |
| Compur 1 | 1 | B, 1-1/500sec | 39X0.75mm | 41.8mm |
| Compur 3 | 3 | B, 1-1/500sec | 62X0.75mm | 65.3mm |