Lenses

Early Lenses

Until the late 1860s the lens types in common use were the Petzval portrait, the single achromat and, to a lesser extent, early triplets and doublets. The Petzval was a fast lens but had a limited angle of view with fall-off of illumination and sharpness at the edges of the plate. The single achromat had a wider angle of view and produced an image with more contrast but was slow.

Non-Anastigmats

The rapid rectilinear, introduced in 1866, became a general purpose lens and the one most often found on cameras of the period. The single achromat continued in use for landscape work while the Petzval became confined to the professional studio.

Anastigmats

The development of new glass types in the late 1880s gave the opportunity to design lenses with better correction for astigmatism and spherical aberration. Lens designs and configurations multiplied from this time and brand names started to be used rather than the descriptive names used previously.

Telephoto

A telephoto lens consists of a negative lens group placed behind a positive group with the intention of reducing the overall lens to focal plane distance compared to the focal length. The first telephoto lenses were from T.R. Dallmeyer and Adolf Miethe both in 1891.

Early models often used a normal prime lens in conjunction with a 'telephoto adapter' providing the negative group. The magnification could be altered by varying the separation between the positive and negative groups; the closer the groups the greater the magnification and the larger the image.

Front of Lens Attachments

Afocal attachments generally take the form of a Galilean telescope mounted in front of a prime lens to produce a telephoto effect, if reversed a wide-angle effect was achieved. The separation of the two lens groups is normally set to be equal to the difference in the two focal lengths, in this arrangement incident parallel rays will emerge parallel. The camera will therefore focus at infinity with its normal bellows extension. The magnification (compared to the image produced by the camera's prime lens) when in this set-up is equal to the ratio of focal lengths of the two lens groups. Prism monoculars (e.g. Zeiss Contaflex) and spotting telescopes have also been used.

Their first use was by Dallmeyer in 1901, in the Adon telephoto. The idea resurfaced in the 1950s for use on fixed lens cameras, especially twin-lens reflex types and cine cameras.

Pin-hole, Enlarging, etc

From the 1880s there was a lot of interest amongst photographers in the artistic effect produced by pin-hole photography; pin-hole 'lenses' were manufactured along with other devices to soften the image and modify the plane of focus.

Lens Diaphragms

This section has details of the various types of diaphragm fitted to lenses and their calibration.

Lens Mounts

This section has details of the different types of lens mount, focusing methods and how the lens was fixed to the camera - screw thread, interrupted thread, bayonet, breech lock.

Lens Notes

Early Lenses

It is not easy to identify an early lens as they did not generally carry a name, they might be marked with the maker's name and perhaps a numeral indicating the series (type of lens) or the size, the focal length and aperture were not engraved on the lens mount. Catalogues of the period would list the lens series and indicate its use, lenses within the series would be shown as suitable for a particular plate size, the back focus (usually called focus) might be shown. Portrait lenses were generally shown as being 'Quick Acting' or something similar, the lens diameter would be given along with the plate size covered, the camera to subject distance may also be shown (to ensure that the lens would be suitable for the studio).

The maker's name can sometimes be found written on the edge of the glass, this was more common with continental manufacturers than British.

It was common for each lens of a stereo pair to be matched to a particular flange and for the waterhouse stops to be matched to the lens. A number or letter was often stamped on the lens and matching flange and stops.

An 'O' has been engraved on one lens and flange from a Dallmeyer stereo camera.

The front group of a Petzval portrait lens was similar to a single achromat and if reversed so that the concave surface faced the subject could be used as a landscape lens. Lens makers did not fully recommend this but many produced lens mount designs that made it easy to adapt the lens for landscape use. In some cases this simply meant that the rear group was removed and replaced by the front group, often a different diaphragm arrangement was needed. Jabez Hughes described several designs at a meeting of the South London Photographic Society on 18 October 1860.¹

Dividing / Combinable

Some lenses could be divided, one or both halves being usable as a long-focus lens. The rapid rectilinear could be used in this way each half-lens having approximately twice the focal length of the combined. The front half of a Petzval could be used a landscape lens when reversed and put behind a diaphragm.

A combinable lens has several lens groups that can be combined or used individually to give a wide range of focal lengths. The Protar series VIIa is of this type.

Lens sets, known as caskets, share a common mount and diaphragm, the lenses in the set, typically a rapid rectilinear, landscape, wide-angle, were not combinable.

Interchangeable Components

A patent by H.D. Taylor proposed the use of interchangeable rear components on a Cooke Triplet that changed the focal length. Some years later T.T.H. supplied 'Extension lenses' giving a 50% or 100% increase in focal length. On the Cooke Series III, IV and V the rear element was changed on the Series II the front.² The Aldis Anastigmat was supplied with interchangeable front components from around 1905, these increased the focal length by 2 and 1.5 times.³ The idea resurfaced in the late 1950s on cameras such as the Contaflex, though these were based on afocal attachments.

Lens Coating

Coating lenses to increase light transmission by chemically altering the surface was proposed by H.D. Taylor in 1904.⁴ No further progress was made with the idea until the late 1930s when Carl Zeiss started coating their lenses by depositing a thin film on the lens surface, a process very different to that of Taylor.⁵

References & Notes