# Photographic lenses

As explained in “Introduction for beginners: What should I get?”, optics have had only minor developments for more than 100 years. Starting from the iconic “Cooke Triplet” available since 1893, there have been many interesting lens designs since then, with each of them holding a unique character, giving each of their images a recognisable look.

## Glass is the enemy

The less glass a lens uses, the better. Always.
As long as there is any medium between the origin of radiation and it’s destination, even if it is just air, there will be absorption. The biggest factor in image quality is the lens, which refracts light it receives, using glass elements doted with other substances. Every element in the lens absorbs part of the light it receives, this effect is additive, meaning the more glass a photographic lens has, the worse it will render the image it is “seeing”. Usually, on top of the purely “image forming” elements, a photographic lens will have “corrective elements” whose only function it is to eliminate an undesirable effect from the output of the lens. There are numerous imaging defects in optics and corrective elements have their place in eliminating those.
Since the advent of digital cameras however, there has been a trend for “perfect” images, free of any character, with immensely high resolution, at the cost of any interesting property the lens might have had. Therefore, some manufacturers include a very high number of corrective elements in an optical design to achieve this, the result being the lens now has high resolution and nothing else. Also, there is an advertising incentive to do this, since resolution is the only optical metric in photography, that can be quantified by a test and therefore is simple to print on a box. A photographic lens always is a holistic design and should be used to communicate a certain mood, enhancing the storytelling of the image the photographer creates; would the story of an image really be made better if the lens is now able to resolve 160 lp/mm, but looking as if it had hand creme smeared all over its front element?

## Zoom and Prime lenses

Photographic lenses belong to one of two classes, “Zoom” or “Prime”. Zoom lenses are able to change their focal length and thus change how much an object is magnified, since this requires more imaging and corrective elements, they are lower quality than prime lenses. Prime lenses cannot do this and therefore have a significantly simpler optical formula and hence are higher quality.

## Adapting Lenses

As mentioned previously, MILCs made lens adapting possible, since MILCs lack a mirror, the sensor mount can be a few millimetres in front of the sensor, while with DSLRs, there needed to be sufficient clearance to accommodate the mirror. The distance between the lens-mount and the sensor is called the "flange distance" and it affects all lenses, since the flange distance needs to be accounted for, when designing a lens. This is important for focus, since if the flange distance is to long or too short, lenses cannot focus properly. Lens adapters are essentially a hollow metal tube, with your lens-mount and camera mount of choice, it’s length is perfectly the distance needed to properly place the adapted mount relative to your sensor.
To start adapting lenses, you only need to know two things, the lens mount of your camera and the mount of your lens. Most MILCs have adapters available for almost all lens mounts ever created, some of them even feature CPU contacts, such that for example, a Fujifilm camera can communicate electronically with a Canon lens.
Almost all older lenses feature an aperture ring, if they do not, they either have a small slit sticking out the back (like the Nikon F mount) or they are exclusively electronically controlled, ask in a shop if you can try them with your adapter of choice, to be safe.

## Optical qualities

Overview of lenses

## Specific lenses

* Canon
** Wide-angle
** Standard
** Telephoto
* Canon special-purpose
** Macro
** Tilt-Shift
* Nikon
** Wide-angle
** Standard
** Telephoto
* Nikon special-purpose
** Macro
** Perspective Correction and Tilt-Shift