PR for People Monthly September 2017 - Page 41

If you are struggling to achieve really sharp images, this article might just help. Lenses are curved pieces of high-quality glass that serve to focus light rays as they enter the camera on a spot behind the lens called the focal plane. The better lenses can focus the light, the sharper the image will be. One of the characteristics of all lenses is that they are made up of a number of elements of glass all spaced in such a way as to make the focusing of light accurate. The further apart these elements are, the more the lens is able to focus on a small part of the scene and magnify it or make it appear larger. The closer together these elements are, the more the lens is able to take in a wider angle of view. If the elements are able to move within the lens (as in a variable focus or zoom lens), the more they will be able to focus on near objects and distant objects both. Movable elements introduce a factor that often makes it difficult for the lens to achieve really sharp results and that factor is that the elements are always moving. Sometimes they can drift out of perfect alignment, causing the image to lose quality. That is not to say that acceptable results can’t be achieved with zoom lenses, but as a rule, they are not as sharp as fixed focus lenses with no movable elements. (And, keep in mind that if you use a normal, "point-and-shoot" digital camera, it will almost always have a built-in zoom lens.) The other factor that determines a lens' sharpness is the quality of the glass used. Obviously, cheaper lenses use cheaper glass. So, again, as a rule, a cheap lens will usually yield images of lesser quality. You can sometimes get an inexpensive lens that happens to be very sharp, but that is the exception, not the rule.

As a lens is used at its largest aperture, more of the edges of the glass are used to focus the light rays. Because of this, the larger the widest aperture, the less the lens will need to be used at that opening to make an acceptable exposure. If the lens can be stopped down one or two f/stops, it will be using more of the center of the lens and less of the edges. This will yield sharper images. In other words, a lens with an aperture of f/1.8 has a larger piece of glass in order to be able to admit a correspondingly larger amount of light. Therefore, this lens, if used at an f/stop of f/2.8 will yield a sharper image than a lens whose largest aperture is f/2.8, because it will be stopped down one or two f/stops, thus using more of the center of the glass. As a lens uses more of its center to focus light rays, its ability to render sharp focus increases up to a certain point. (Within the lens, the shutter blades themselves can cause some refraction of light. So, if a lens is stopped down to its minimum aperture (say f/16 or f/22) some refraction will usually take place that alters the sharpness of the image even though you will get more depth-of-field at smaller apertures. So, you have to make tests to see if there is any fall off of sharpness at those small apertures. In addition, the number of blades that make up the shutter affect the overall sharpness as well. Better lenses have more shutter blades and consequently yield a rounder aperture. This would help a lens' overall sharpness.

A view camera with bellows and separate front (which has the lens) and the back (which has the focal plane), can be adjusted to provide infinite focus at just about any f/stop. Digital cameras, however, do not have this feature. So, the only way to achieve really sharp focus is by using the lens and ISO settings correctly.

The point of all of this is that if a good lens is used a couple of stops from wide open and/or a couple of stops from its minimum aperture, it will probably achieve its maximum sharpness. For photographers intent on

Image Sharpness With Digital Lenses

by William Lulow