It’s all about the lens

Posted in Analog photography
1436 words
Estimated reading time: 7 min read

There are so many photography lenses, for different purposes and uses, that give different results; lenses vary in size and in price. Construction of camera lens is very complex process, so don’t be surprised if the lens you put your mind on costs a lot of money. Nowadays, when digital photography took over the analog process of making images, lenses that were used on old cameras are still mountable on fancy DSLR cameras. That’s mostly because of the fact that they give high quality photo and they are almost impossible to destroy. Good camera lens definitely worth a lot and it’s most certainly one of the most responsible things for good photo, if not the most important all in all.

Before we get into the field of construction of the lens, it’s important to know what kind of lenses there are – prime lenses (the ones who’s focal length is fixed, as opposed to zoom lenses), zoom lenses (focal length is changeable, they cover a range of focal lengths by movable elements within the lens), normal lenses (focal length is about equal to the diagonal of the film), wide-angle lenses (focal length is way smaller than with normal lenses), telephoto lenses (focal length is way bigger than with normal lenses), catadioptric lenses (form of telephoto lens but with a light path that doubles back on itself and with an objective that is a mirror combined with some form aberration correcting lens).

Anatomy of a Lens

The complexity of a lens varies from lens to lens, the angle of view, the maximum aperture, type of lens and its purpose and many other things affect its construction. Each lens is made up from a number of separate elements arranged along a common axis.

There are many different kinds of materials used for making lenses. The most of them consist of either optical glass or transparent plastic material like acrylic glass or plexiglass, and some early lenses have elements filled with water. Construction of some special lenses, like super-tele, that have mirror elements which can be made of variety of materials. Optical materials are being chosen by their ability to refract light. Although in contemporary photography optical plastics are increasingly common, for old lenses it was much more common to use glass. There are two types of glass used for lenses, crown glass and flint glass.

Lenses are designed with many different complex optical formulas that reduce or correct lens aberrations, distortion and vignetting. Lenses are often made with different special coatings to decrease internal reflections, improve sharpness, contrast, and reduce flare.

In the process of constructing a lens it’s not just enough to place pieces of glass together. First of all, elements are separated into two groups – converging (light-focusing) and diverging (light-spreading) elements.

Two or more elements which are fixed together without an air space between them make a group, on old lenses the thing that ‘glued’ the elements together was Canada balsam, mixture specially made from tree sap.

After roughly shaping an appropriate type of glass, its surfaces must be ground until spherical concave or convex surfaces get the desired, mathematically-calculated and incredibly precise curve.

The barrel of the lens is the outer shell that contains all of the lens elements. The aperture is a circular (or approximately circular) opening, or if you prefer, a hole, usually placed between the lens elements, that controls the amount of light passing through it into the camera. In addition to adjusting the light intensity passing through the lens, aperture controls the depth of field (smaller lens apertures increase depth of field). Aperture is in fact multi-leaf diaphragm, usually adjustable in diameter, and the lens’s optical axis passes through the center of the hole.

Mount is metal ring placed in the back of a lens, its job is to fix lens to a camera body.

Geometry of a lens

The optical axis mentioned earlier is an imaginary line which goes through the centers of the curvature of the lens elements and meets the focal plane at exactly 90-degree angle. The focal plane is the area onto which a lens projects the image of the focused image subject. In order to everything work properly, the position of the film’s light-sensitive surface should be identical with the focal plane. The focal length of a lens is the distance from the focal plane to the optical center, placed on the optical axis. Nowadays, the most common measure of focal length is in millimeters, but inches or centimeters are also in use.

History of a lens

Photographers and inventors Thomas Wedgwood, Nicéphore Niépce, Henry Fox Talbot, and Louis Daguerre, who did much in the field of old photography processes all used simple single element convex lens for their experiments and research. This soon turned out to be not enough, because this simple lens could not focus the image properly, especially over a large film plane. What also appeared as problem were all kinds of optical and chromatic aberrations. In the 1829, inventor Charles Chevalier has introduced a two-glass lens made out of flint and crown glass in order to minimize aberrations that surfaced during Daguerre’s experiments. The lens had the reverse concave flint glass side facing the subject and the design was reasonably good, so it was quickly copied from many other lens makers.

The next big breakthrough in the field of lens inventing was The Petzval Portrait lens in 1840, invented by a Slovak math professor Joseph Pretzval. It consisted of four elements: a front cemented achromat and a rear air-spaced achromat. The Portrait was widely illegally copied by every lens maker and Petzval had a growing conflict with Peter Voigtländer about unpayable royalties.

Symmetry in optics soon appeared as a good idea – it solved many problems – it solved three out of seven aberrations.

In 1862 the first successful wide angle made its appearance (92° maximum field of view; 80° was more realistic) and lens was the Harrison & Schnitzer Globe. Charles Harrison and Joseph Schnitzer’s Globe had a symmetric four element formula and it’s named by the fact that if the two outer surfaces were continued and joined, they would form a sphere. The design of the Globe directly influenced and inspired the creation of the Dallmeyer Rapid-Rectilinear and Steinheil Aplanat in 1866, that individually created and developed, accidentally had the identical construction that corrected most optical aberrations, except for spherical and field curvature.

In 19th Century, the Portrait, the Globe and the Rapid-Rectilinear/Aplanat were the only lens models constructed worth mentioning.

By the end of 1891, Thomas Dallmeyer and Adolph Miethe simultaneously attempted to patent new lens designs with nearly identical construction – complete photographic telephoto lens consisting of a front achromat doublet and rear achromat triplet. No patent was ever granted for the first telephoto, because the primacy could not be proved, though both of them tried. The first officially accepted and successful telephoto lens that was optically correct appeared in 1905, and it was Busch Bis-Telar lens.

In 1902 Paul Rudolph developed the Tessar, the treasure of the early 20th century. The Tessar was originally an f/6.3 lens and was refined to f/2.8 by the 1930, although to the end f/3.5 was the realistic limit of this lens, in order to get the biggest quality of the image.

In 1950, the Angénieux Retrofocus Type R1 35mm f/2.5 was the first retro focus wide angle lens for 35mm film camera. The original term used for this wasn’t retrofocus, but reversed or inverted telephoto. It’s a lens that consists of positive and negative cells placed on front and rear. Soon after the invention of retrofocus lens, inventors were inspired to invent its opposite brother, non-retrofocus lens. In 1954 Zeiss Biogon 21mm f/4.5 was released, and its evolution, the Zeiss Hologon 15mm f/8 in 1969.

As for the fisheye lens, the first ever was invented in 1923 and it was the Beck Hill Sky (sometimes called simply ‘Cloud’). The Beck Hill Sky was 21mm f/8 producing 63mm diameter images. Zoom lenses came a bit later; the earliest zooms appeared in market sometimes between 1929 and 1932 and were called “Traveling,” “Vario” and “Varo” lenses.

Probably the most interesting type of lens, by the scientific side is the catadioptric “mirror” lens, because it combines variety of other inventions and techniques. It’s a specific combination of elements – Catadioptric Mangin mirror (1874), Schmidt camera (1931), and the Maksutov telescope (1941) along with Laurent Cassegrain’s Cassegrain telescope (1672). The first to incorporate successfully all of these elements into one working super telephoto was Russian inventor Dmitri Maksutov with his MTO (Maksutov Tele-Optic) 500mm f/8, in 1944.