camera Lenses
The Single-lens Reflex (SLR) camera's construction allows it to use a wide variety of interchangeable lenses for obtaining optimal photography. One of the distinguishing characteristic of SLR camera is the viewfinder system. As the image that reaches the focal plane can be viewed using the viewfinder, the image which is to be captured can be checked in prior.
A mirror in front of the lens is used to deflect the light rays, which pass through in upward direction to be shown on a focusing screen. The deflected image is then correctly oriented and projected by using a pentaprism before it is seen through the eyepiece. Upon pressing the shutter button, the mirror rises up exposing the film to the image sensor. The mirror then returns to its original position once the shutter is closed.
This system enables the photographer to accurately frame the images without being affected by parallax phenomenon, which has different light paths for the viewfinder and shooting lens.
Focal Length: Is the photographic lens's basic description and generally represented in millimeters (mm). Focal length is the optical distance from the object to the camera sensor at the focal plane in the camera. Longer focal length results in narrower view angle and higher magnification. On the other hand, shorter focal length results in view angle and lower magnification.
Different Focal Lengths for Different Images: The impression of a photograph can be varied largely by using a variety of lenses for serving different purposes. The differences in the focal length of the lens substantially changes the angle of view (range), depth of field, and perspective of the subject to be photographed. The angle of view is called as the angle of range and it is generally shown as the angle of the diagonal direction. Normally, the image taken by the lens is circular and is called as an image circle. The actual photographed image is taken from the center of the image circle.
Depth of Field: Is the distance between the closest and farthest objects in a photo. In narrow depth of field, only a small part of the image is in focus. Whereas, in large depth of field, majority of the scene comes into focus
Aperture: Is the small opening in lens that lets light in and project to the sensor. It works like the pupil for eye lens. Most photographers change aperture when it comes to adjusting the depth of field. Large apertures have small f-stop values and produce a shallower depth of field. On the other hand, small apertures have large f-stop numbers produce images with a large depth of field.
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