Regardless of image size or design, a camera should possess the following controls and settings, whether manual or automated:
- Precision Aiming and Composition: An effective method for accurately pointing and composing the image.
- Focus Capability: The ability to achieve precise focus.
- Shutter Control: Manages exposure time and the duration of light exposure on the sensitive surface.
- Aperture Control: Regulates image brightness and depth of field.
- Film Management: A system for loading and unloading film without exposure to unwanted light.
- Light Meter: Measures light and indicates or adjusts the exposure required for each shot.
Composition and Focusing
The oldest and most rudimentary method of composing and focusing images is still used in large format cameras for professional photography. These cameras feature a ground glass display at the back, allowing the photographer to see and focus on the real image created by the lens.
Once the film is loaded into these cameras, the image is no longer visible on the screen. An alternative arrangement, originating from early amateur cameras, is to have a direct line of sight embedded in the camera body, similar to today’s compact cameras. This provides a separate, direct view of the subject, matching the viewing angle and aspect ratio of the image captured by the camera lens.
However, this direct vision finder has limitations. While it frames distant subjects accurately, as you move closer to the subject, the viewfinder’s perspective becomes increasingly misaligned and imprecise due to the separate, parallel viewpoints of the camera lens and the viewfinder, known as “parallax error.” A correction line in the viewfinder window should indicate the true top of the image when photographing at close range.
For focusing with a direct viewfinder, basic types may have a simple control that aligns the lens based on a series of preset symbols representing various subject distances. High-quality 35mm or medium-format direct-sight cameras often feature a precision manual rangefinder system. Many modern compact cameras now include an automated remote sensing system for autofocus (AF). When you begin pressing the shutter button, the camera measures the distance to the subject electronically and automatically adjusts the focus accordingly.
Lens Adjustments and Aperture Control
Single-lens reflex (SLR) cameras are designed to keep the lens aperture wide open while you compose and focus the image. They employ a mirror behind the lens to reflect the image onto a focus screen near the top of the camera body. This mirror moves out of the way just before exposure. The focus screen provides an exact representation of the visual effects of depth of field at different apertures, ensuring “what you see is what you get.”
For precise depth of field control, SLR cameras allow you to preview the portion of the image that will be in focus at different aperture settings. This feature is known as depth of field preview. Most modern 35mm SLR cameras come with autofocus capabilities but also allow for manual focusing.
