November 14, 2013

Camera lenses. What they are and how to choose them in photography. Part I

A camera lens is an optical device which captures the light in a scene and focus it onto the film or digital sensor. It is made of several lens elements: extra refractive glass (which alters the angle of refractive light), aspherical elements (correcting into focus peripheral rays), low dispersion elements (which reduce chromatic aberration), anomalous dispersion elements (to control the amount of diffraction of light for a specific color range). The quality of these elements will determine the whole quality of  lens and image captured.

Lens is probably the most important part of a camera so you should carefully choose it when buying a new camera or upgrading a lens. But, with so many options out there,  which one should you choose?

To answer this question you need to answer several other questions, like which focal length you need, which the maximum aperture, or the fastest focusing, or the sharpest image, or the softest bokeh...  You also need to know the size of the sensor or your camera because the focal length may change: to make a focal length of 50mmm on 35film (or full sensor) equivalent on APS-C sensor (which is smaller) you need a 35mm while you need a 25mm for the micro 4/3 (even smaller) or a 80mm for a medium format (bigger than 35mm). The best advise is to choose your camera lens according to what you photograph and to your photographic style. But you have to know about lenses to be able to make the right choice. So let's have a look at them!

Standard lenses. When a lens has a focal depth in the range between 35mm and 70mm it is called standard lens because it resembles the way the human eye sees things (about 50mm on a 35mm film): subjects will have the same size and the same proportions as seen trough the eyes. They are general purpose lenses, ideal for the kind of shots people normally take. This is the range that the kit zoom lenses supplied with the camera cover: these are very cheap lenses that do their job but the quality is quite poor; so, if you want to get any serious about photography, change them!

Wide-angle lenses. When a lens has a focal length minor than 35mm it is considered a wide-angle. Most people say that they use these lenses to fit the scene in the shot when they can't move further away: don't listen to them! This use is very reductive for a wide angle lens; photographers use it for the opposite reason: to get closer to the subject (street photographers make great use of these lenses). The wider vision and the really close minimum focus distance are characteristics that play in favour of creativity. Wide-angle lenses exaggerates the relative proportion of objects at different distance, making the closer one appear bigger; this emphasizes objects in the foreground but can turn a portrait in a caricature.  Line and curves are exaggerated too due to the barrel distortion; photographing converging lines can be tricky (you should always aim to the horizon to avoid them or correcting them with an edition software if you don't have a tilt-shift lens). One more thing to take care of while shooting with wide-angle lenses is the light changes throughout the image due to wide portion of the scene in the frame, both horizontally (this variation can be corrected with GDN filter or bracketing for HDR) and vertically attention to the position of the light source is needed: the closer the light source is to the frame, the whiter will be the image (think of a clear sky, with the sun out of frame, which turns from deep blue to white).

If the focal length is greater than 70mm the lens is called telephoto.  Do you want to know more about it? Stay tuned for part 2!

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