Controlling depth-of-field

Medium format lenses need longer focal lengths than 35mm to cover the same area. A 100mm lens is considered normal in 6X7 format, but telephoto in 35mm. Used on a 6X7 camera, a 100mm lens has about the same angle of view as 50mm lens, but it still gives the same depth-of-field as a 100mm on a 35mm camera. Many people overlook this when working with medium format lenses. Lenses with the same focal lengths give the same depth-of-field on all formats. A 100mm lens gives the same depth-of-field on a 35mm, 6X7, or 4X5 camera. To get proper depth-of-field you need to focus more carefully. To get everything in sharp focus in a landscape for instance, a 20mm lens on a 35mm camera set at f-16 might provide enough depth-of-field, but a 45mm which has about the same angle of view on a medium format camera, needs to be closed down more. Even closing the lens to its minimum aperture may not give enough depth-of-field, plus you may loose overall sharpness due to diffraction.

Wide-angle lens and small f-16 aperture produced sharp foreground and background

You have two tools to work with to check depth-of-field. One is the depth-of-field scale and the other, depth-of-field preview. Use the preview button to close the lens down to the working aperture. This darkens the view, but you can check depth-of-field. If depth-of-field is not enough, try focusing on the near and far end of the scene. Check the distance scale on the lens and turn focusing ring until both ends are equally placed on both sides. See the mark for the aperture required to cover depth-of-field.


Shallow depth-of-field due to use of telephoto lens and large aperture

Since the plane of focus is parallel to the film, you must choose it very carefully. Even a slight camera movement, up or down, can change depth-of-field. An alternative is to use tilt and shift lenses to change the plane of focus by moving the lens instead of the camera. when working with regular lenses and you still can't get the depth-of-field you need, try a different focal length or move back. It is not always possible to get everything in sharp focus with any format. Know your lens capability and practice by focusing on near and far subject at different f-stops to see how far you can push each of your lenses to get the best depth-of-field.