Every adoring enthusiast and professional knows the trick. You take almost any Canon DSLR, you place one of their numerous L-Series lenses on the front and when you have finally taken a picture (presumably at a decent exposure), you notice something special has taken place in the process of capturing light, something quite sublime. You look on your LCD screen and the colours seem to pop more then usual. It’s as if the texture of a surface in a shot can be felt as well as seen. A surfeit of detail, that the eye may not have even registered, spills out of the image you have just recorded, but also created.
It’s a fairly old trick now, a trick that will run and run. But on reflection, it must be noted, that it’s no trick at all. Merely science. The question is how have Canon created such stunning specimens of optical technology? What distinguished elements sit bellow the slick black, or grand white outer shell, which are adorned by that notorious red stripe? What is it that makes a Canon Luxury Series Lens so special?
The obvious answer is, of course, the glass. But that in itself poses more questions. What type of glass exactly?
Ultra-low dispersion (or UD) glass
Canon specifically use the term Ultra-low dispersion to describe some the elements contained in their lenses. Other brands use phrases such as ED (Extra-low dispersion), SLD (Special-low dispersion) or UL glass. Despite the differences in name, these all work with the same theory, namely that the dispersion (or scattering) of light as it travels through the lens often produces unattractive fringes of colour around the boundaries of lighter and darker parts of the image. This effect is known as chromatic aberration and it is the inevitable consequence of photons of light being made up of different wavelengths and the fact of these wavelengths producing different colours. Often light becomes uneven and refracted by the time it hits an image sensor, thus in the image we see something quite unlike what we experience with our eyes, which are, in most respects, more complex and intuitive then camera lenses. But UD elements make up for that by reunifying photons of light to a single point. However, UD glass only reduces the effects of dispersion and there are other factors that can create visual discrepancies when light traverses a lens.
As previously mentioned, UD glass does a great part of the work in reducing chromatic aberration, as does another element known as Fluorite. Produced using a type of crystal which is mostly for smelting and in the production of certain enamels, the mineral (sometimes known as fluorspar) is mined in numerous parts of the world including the Erongo Mountains in Namibia, though it is quite well known that Canon produce it synthetically. Fluorite is not used in as many lenses as UD glass and the manner in which it handles light dispersion is similar yet infinitely more complex. Because of its high clarity it seems wavelengths of light resulting in either inferred or ultraviolet have less chance of interfering or complicating the contrast between light and dark in the image when they pass through a Flourite element.
So far most of the distortions that occur in capturing light sound rather subtle and for the most part this is the case. It’s a rare thing for us to see colour fringing unless we zoom into the image several times over or blow a picture up on a huge screen. But it’s the small things that count. It’s the tiny fragments of precision and problem solving that L-Series lenses help to rectify and the results both in camera and off are ultimately quite stark.
The last type glass I will discuss is known as an aspherical element. In addition to light dispersion and chromatic aberration, one other defect which can occur in image creation is spherical aberration. Light tends to travel in an orderly fashion at the centre of a glass element (hence why most images are sharpest at their centre), but light waves which traverse the far corners have a tendency to refract and interfere with the light in other areas. Again this leads to the type of visual distortion, which you may or may not notice in camera. But the important thing is how similar or different the image is to what our eyes see. Human vision is always the chief reference point. So if a lens can either emulate human sight or produce something even better then it, we are in for a treat. An aspherical element attempts to do this, possibly, in the most accurate sense. Like a corrective pair of contact lenses or eye glasses, aspheric elements have a more complex front surface that gradually changes in curvature from the center of the glass out to the edge thus making it less likely that photons will refract as they cross the edges of the lens. This leads to a far more pleasing visual, in which sharpness is distributed across far more of the overall image then it would otherwise.
At Park Cameras, we hold the range of Canon lenses in stock most of time. For directions to our stores, please click here. Alternatively, visit www.parkcameras.com for the range of Canon lenses, including the L-series models.
Missed part 1? Click here to read the post.