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The two main optical parameters of a photographic lens are the maximum aperture and the focal length. The focal length determines the angle of view, and the size of the image relative to that of the object, while the maximum aperture limits the brightness of the image and the fastest shutter speed usable. A popular third consideration is close focusing distance.
The maximum usable aperture of a lens is usually specified as the focal ratio or f-number, which is equal to the focal length divided by the effective aperture (or entrance pupil) diameter in the same units. The lower the number, the more light per unit area is delivered to the focal plane. Larger apertures (smaller f-numbers) provide a much shallower depth of field than smaller apertures, other conditions being equal. Practical lens assemblies may also contain mechanisms to deal with measuring light, to hold the aperture open until the instant of exposure to allow SLR cameras to focus with a brighter image with shallower depth of field, theoretically allowing better focus accuracy.
Focal lengths are usually specified in millimetres (mm), but
Photographic camera became a desired consumer item since it became handheld many years ago. As it became digital with no need for film processing, digital camera became even more popular and it is now considered one of the most wanted optical/electronic consumer products.
However buying a digital camera may be a bit difficult due to the many brands and models being offered. After all there are so many features, one has to be sure of his needs in picking the right digital camera. The following tips might of some help:
1 – Price range: It is recommended that you establish a price range you are willing to pay for your new digital camera. Prices can start from bellow a hundred up to thousands of dollars.
Resolution
The amount of detail that a camera can capture is called the resolution, and it is measured in pixels. The more pixels a camera has, the more detail it can capture and the larger pictures can be without becoming blurry or “grainy.” High-end consumer cameras can capture over 12 million pixels. Some professional cameras support over 16 million pixels (megapixels), or 20 million pixels for large-format cameras. For comparison, it has been estimated that the quality of 35mm film is about 20 million pixels.
Exposure and Focus
Just as with film, a digital camera has to control the amount of light that reaches the sensor. The two components it uses to do this, the aperture and shutter speed, are also present on conventional cameras.
Aperture: The size of the opening in the camera. The aperture is automatic in most digital cameras, but some allow manual adjustment to give professionals and hobbyists more control over the final image.
