One of Adams specialities was a brilliant finder with triple lenses. It was fitted to better quality cameras. Produced in three sizes in either brass or aluminium.

The Cornex used a frame at the focal point of the front lens to outline the field of view, on some versions the frame could be rotated for portrait or landscape.

A very expensive finder that did not sell well. Price 25/-.

The term 'view-meter' usually described a hand-held finder used to assess the scene and the best viewpoint and, if adjustable, which lens to use. A view-finder referred to a finder attached to a camera showing what will appear on the negative, but the terminology was not rigid. The main types are described below:

Frame Finders

An unusual arrangement was fitted to some pre-war Rolleiflex cameras, there was no back sight, the frame carried at its centre a small concave mirror with a hole in its centre. The photographer looked into the mirror and centred the reflected image of his eye with the small hole.

Reflecting

Brilliant

Prism

• Pentaprism

  These were intended as waist-level finders, a pentaprism (five parallel sides) is used to produce an image that is upright and not laterally reversed. A negative lens may be in front of the prism to determine the field of view. This type of prism was first used (on cameras) by Adams in the Rectiflex finder. Later models were the Aufsu for the Leica. Despite giving a much clearer image than brilliant finders they did not prove popular.

• Richard Roof Prism

  This is a prism with four triangular faces - two reflecting surface (the roof), an entry and an exit surface. It was intended to replace the mirror of a waist-level finder. The prism deflects the image through 90 degrees and corrects the laterally reversed, inverted image produced by the front lens. The description shows the prism sitting behind a positive lens and below a ground glass screen or a lens, mirrors could have been used in place of the prism.²

Double Mirror

Curved Mirror

Direct Vision (Eye-level)

• Single Lens

  A concave lens usually having cross hairs giving a reduced image of the field of view. Popular in the 1890s.

• Lens/Post

  Similar to the above but with a rear sight added.

• Post/Lens

  The reverse arrangement to the above, more popular on continental cameras than in Britain.

• Lens/Lens (Reverse Galilean)

  Consists of a front negative lens and a positive rear lens. Sometimes enclosed in a tube. The rear lens may be of blue glass to remove tonal values. This basic finder was later developed to include suspended frames for different lenses.

• Without lens

  Consists of a simple tube with a mask to outline the field of view, sometimes with plain glass, front and rear. This could be considered a frame finder but was much smaller. Used on Periflex cameras with long-focus lenses.

• Telescope, Monocular

  Consists of a miniature telescope or monocular with a positive objective lens, eyepiece and probably an image erecting prism.⁵

• Universal

  Similar to a lens/lens type but for multiple focal lengths. The simplest has the field outlines for several lenses drawn on a transparent mask. The Leitz Vidom finder had two L shaped masks which were slid together or apart as the lens was selected; the image remained the same size but the image frame changed. The front, image forming, lens was converging, an erecting prism (Dove type) was fitted giving an upright but reversed image. Zeiss used a fixed rear component with several converging front components of different strengths, this had the advantage that the image size changed within a fixed frame. Porro prisms erected and reversed the image. Another option was a varifocal arrangement having a moving lens component, used on the Kodak Ektra.

Albada

Suspended Frame

Direct Ground Glass

Opaque

For Reflex Cameras

• Single Mirror

  The simplest was to set a mirror in the hood parallel to the reflex mirror. This gave an upside down, laterally reversed image, which was considered a drawback. Despite this, single mirrors are found on many reflex cameras including early Rolleiflex models, an accessory was available for the Soho that fitted to the top of the focusing hood.

• Two Mirrors

  Having two angled mirrors with their line of intersection horizontal and at right angles to the lens axis gave an upright image that was laterally reversed. This solution was used on the Wrayflex camera, 1951, but similar designs date to E.L. Doyen's patent of 1897.⁸
• Three Mirrors

  Two mirrors arranged above the focusing screen with their line of intersection parallel and to one side of the lens axis (forming a roof) reflect the image down to a third mirror at 45 degrees which directs the image to a finder; this gives an image that was upright and not laterally reversed. This arrangement was used on the Gamma Duflex of around 1948. Other three-mirror arrangements are possible.
• Roof Prism

  These have unfortunately acquired the name of pentaprism, equally unfortunate is the usual diagram showing the light-path. They consist of an entry surface with two reflecting surfaces (the roof) angled at 90 degrees above the entry surface and set at an angle to the horizontal. The two reflecting surfaces both reflect incoming rays to the opposite surface, due to the tilt they then reflect the light to the front of the prism, where a third reflecting surface directs the light to the finder. The other surfaces are not used. The prism laterally reverses the image without inverting it. First used on the Contax S, 1949, though there were earlier proposals. Roof prisms were available for cameras with fixed waist-level finders where they would sit either inside or on top of the hood.

A condenser lens is often sited above the focusing screen to deflect light at the margins of the screen to the eye, an early example is the Stevens condenser fitted to some Thornton-Pickard cameras in the 1930s and the Contaflex of 1935.⁹ A Fresnel screen serves the same purpose with less weight and bulk.

Parallax

Rising Front

The illustrations show an N&G finder (right) where the front lens can be raised, the indicated value is then set on the rising front. The Sinclair finder (middle) was similar except it tilted. The Adams Identoscope finder (far right) used a lever, as the camera's front was raised the tail of the lever moved against a fixed pin, the top of the lever lifted the lens of the finder.