Optically filters were either made from dyed-in-the-mass glass of from a coloured film usually mounted between glass. Filters were usually placed in front of the lens but can be mounted behind the lens or between the lens elements. The term 'screen' was often used rather than filter. The main types are:
CorrectionThese are pale to medium yellow in colour to correct for the over sensitivity at the blue end of the spectrum of orthochromatic plates. Often sold as 'isochromatic screens'. Special filters were sold for colour plates such as Autochrome. The Zeiss Ducar correction filter for Autochrome or Agfa colour plates incorporated a negative lens to displace the image further from the lens to compensate for the emulsion being behind the plate, the filter was put in place after focusing.1 Colour correction filters for early colour processes were produced in different strengths for different times of the day.
ContrastUsed to modify the tones of a black and white negative. Yellow and green filters, similar to correction types, were used quite early, orange became popular in the late 1930s. Graduated 'sky' filters - part yellow, part clear - became popular in the 1920s but were available earlier.2
Three-Colour ProcessFilter sets for producing separation negatives.
Colour BalanceTo correct for the colour temperature of the light source. Blue filters were produced for using panchromatic films in half-watt lighting. Later pale blue and amber filters were used with colour film to correct colour casts and for using, for example, tungsten balanced film in daylight.
UVThese reduce the transmission of ultra violet light, of use when photographing distant scenes where ultra violet light is especially scattered resulting in lower contrast.
PolarisingThese pass light polarised in one plane while largely eliminating light polarised at right angles to that plane. Originally used to control reflections from non-metallic surfaces. Commercially available from the late 1930s.
Filter Comparisons (approximate)
|Pale yellow||Alpha, 104||K1||201||G1||L|
|Yellow||ISO, 105||K2, 8||202||G2||D|
|Deep Yellow||Delta, 109||K3, G, 15||300||G3|
|Pale Yellow-UV||Aviol, 102||200||G0|
|Yellow/Green||Gamma, 402||G.R 5, GR50||VG4|
|Pale Green||Beta, 401||X1, 11||601|
|Green||X2||602||G.R 10, GR55|
|Pale Red||203, 204||A, 25||901||R10||RG1|
|Deep Red||F, 29|
|Tricolour||A B C|
|Infra-red||207||87, 88a, 91||R20, R30||RG8|
|Light Blue||HS, 301||H|
|Blue||HW, 403||H||801, 802||B5, B40|
K3, used with panchromatic plates, was obsolete around 1932. X1 and X2 were introduced around 1932.
Filters were also produced for visual use. These appeared at quite an early period, Wratten & Wainwright produced a Monochromatic Viewing filter by 1912.
MV Monochromatic VisionShows the scene without colour with the differences in brightness as would be seen by a non-colour sensitive emulsion. Dark yellow.
PV Panchromatic VisionShows the scene as seen by panchromatic emulsion. Used in conjunction with a contrast filter to judge its effect. Purple in colour.
References:BJA 1902, pp. 742, 885. BJA 1909, p. 647. BJA 1948, p. 117. BJA 1957, p. 431. Kodak Museum Cat.Filter Comparisons: Westminster Cat. 1939, p. 23. Minit&Cine, 1938, p. 249. ZI Cat. 1937, p. 98. Contax Photography (1938), p. 46. Johnsons Year Book 1956, p. 27. Ilford Plates & Films, p. viii. Phot. Journal 7/1932, p. x.
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 FindersThese have no lenses and consist of a rear sight and a frame some distance to the front marking the subject area. Often the sight is adjustable for parallax. Available in hand-held form from the 1850s.
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.
ReflectingA positive lens in front of a mirror casts an image on to a horizontal ground glass screen, the lens might be adjustable for rising front. Parallax correction lines were sometimes marked on the screen or, rarely, the lens may be movable. The image is upright but laterally reversed. Largely replaced by the Brilliant finder.
BrilliantSimilar to the reflecting finder but with a positive lens in place of the screen. The image is upright but laterally reversed. Adams & Co. claim to have introduced this type of finder in 1894, which may be the case. From that time the brilliant finder started to replace the reflecting type. Beck introduced an improvement by raising the top lens and including a frame-mask at the focal point of the object lens to give a much clearer outline of the field of view. Large brilliant finders were used on some twin-lens reflex cameras such as the Voigtländer Brilliant.3
PentaprismThese 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 PrismThis 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.4
Double MirrorThere were surprisingly few designs for waist-level finders employing two mirrors enclosing an acute angle, one design made use of curved mirrors.5
Curved MirrorThis comprises a doubly curved mirror and a sighting post. The finder is used at chest level. The mirror is set at 45 degrees, from the side, in vertical cross section it is concave, from the front it is convex in cross section (a saddle surface). The finder gave an upright, laterally correct image. A small horizontal post was used to align the eye to the centre of the mirror.6
Direct Vision (Eye-level)
Single LensA concave lens usually having cross hairs giving a reduced image of the field of view. Popular in the 1890s.
Lens/PostSimilar to the above but with a rear sight added.
Post/LensThe 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 lensConsists 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, MonocularConsists of a miniature telescope or monocular with a positive objective lens, eyepiece and probably an image erecting prism.7
UniversalSimilar 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.
AlbadaThe original pattern had a semi-silvered lens with a concave inner surface but of neutral power placed a short distance in front of an opaque sheet with a sighting hole at its centre. The inner surface of the sheet was black with an outline of the field of view in white. The finder was open, the field of view outline was reflected by the semi-silvered lens back to the eye making it appear suspended on the subject. Several variations exist notably combining it with a lens/lens type finder. The field of view outline for several lenses or images sizes were often combined in one finder. First used on accessory finders for the Contax, 1932, and then on the Contaflex, 1935.
Suspended FrameA development of the Albada finder was to display frame markings within a Direct Vision finder of the reverse Galilean form. A separate window with diffuser illuminated the frames which were superimposed in the finder by a semi-silvered mirror or similar. Frame markings for different lenses could be displayed selectable by interchanging the camera lens, this was usually achieved by a masking plate moving relative to the plate carrying the frame outlines but optical arrangements were possible. When integrated into the camera, compensation for parallax and field reduction when focusing at close distances might be included.
Direct Ground GlassA positive lens giving an image on a ground glass screen. A mirror may be placed behind the screen.8
OpaqueA positive lens is focused on a ground glass on which is drawn an outline of the field of view. The subject is viewed with one eye direct, the other looks into the finder. The two images merge to give an outline of the image area superimposed on the subject. Never popular but used on the Kern Bijou of the early 1920s. A variant was the opaque spot without an outline used on the 1895 model Verascope.9
For Reflex CamerasThese form a special case in that, generally, the image has been cast on to a horizontal focusing screen by a mirror, the image is upright but laterally reversed. The hood to the finder usually incorporated a magnifier and quite often fold-down sections to provide a frame finder. Various options exist to provide eye-level viewing:
Single MirrorThe 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 MirrorsHaving 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 1897.10
Three MirrorsTwo 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 PrismThese 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 1935.11 A Fresnel screen serves the same purpose with less weight and bulk.
ParallaxParallax, the difference in view point of the camera lens and the finder, was overcome in several ways. The simplest was to manually tilt the finder, on frame finders the rear sight could be raised. Automatic correction was provided on some twin-lens reflex cameras, on the Rolleicord masks in the view-finder were adjusted by the focusing mechanism, on the Voigtländer Superb the viewing lens tilted. The first rangefinder camera with parallax correction was the Kodak Ektra, 1941, where a movable lens, inside the finder, was coupled to the focusing mechanism. Other cameras used a movable frame. Leitz produced a variable length extension tube for close-up work in 1935 (nooky) with parallax correction by a moving frame, the frame also compensated for the reducing field of view. A thin wedge in front of the rangefinder window allowed the rangefinder to be used to focus.
Rising FrontWith a brilliant or reflecting finder, raising the front lens would show the effect of rising front. On some finders this was manually adjusted (e.g. Sibyl) on others such as the Adams Identoscope finder the lens was connected by levers to the rising front and was adjusted automatically. Thornton-Pickard proposed having a plumb bob visible in the finder so that tilting the camera would register the amount of back tilt needed to keep the image vertical. In the finder of some Linhof cameras a pendulum shows whether the camera is tilted.12
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.
References:PA 1891 shows some early finders.
With the increasing use of hand cameras where focusing on a ground glass screen was impossible or inconvenient, separate distance meters came to be used. Originally these were called distance meters or telemeters, the term rangefinder applied to the 'two position' optical devices was used a few years later. Some common arrangements are listed below.
Subject Angle (Declination)These work by aiming a sight at an object, a level or plumb bob will then show the angle the object makes to the horizontal which can be converted into a distance. Popular examples work on a quadrant and plumb bob (Primus, N&G) or built into a view-finder where a level indicates the distance which is marked on the finder lens (Watson).13
Standard Subject SizeThese are based on the principle that the height of a person or the size of a persons head does not differ greatly. By measuring the size of the image of the person at the camera the approximate distance of that person is given. An early patent was for the legs of a pair of callipers to be adjusted until they matched the subject (person), the callipers were connected to the lens so that making the adjustment focused the lens. A much later implementation was on a Ricoh camera where the view-finder showed a lozenge shape that changed in size as the camera was focused, the lozenge matched the size of a persons head.14
Focusing TubeMore or less a camera in tubular form with a lens at one end and a focusing screen at the other, the distance could be read from a scale after focusing.15
Optical, 'Two Positions'The object is viewed from two positions, the angle subtended by the object gives the distance.16
Woodbury 1914Two fixed mirrors are used. The image from one is deflected by a small amount by a lens combination, in the neutral position the deflection produced by the lenses is zero. The positive part of the lens combination remains fixed to the baseboard, the negative lens (and mirrors, camera lens, front standard etc.) move forward and back along the baseboard so altering the deflection produced by the lens combination.17
Swing MirrorThe subject is viewed by two separated mirrors. One mirror swivels changing the angle of the reflected image. A very popular construction as it is easy to manufacture. Used on the Contax 1.
Swing PrismA prism is used in place of the mirror. Used in the Leica camera.
Rotating WedgeTwo fixed mirrors are used. In front of one mirror two shallow prisms are arranged, these rotate in opposite directions and so change their deflection and the line of sight. This form requires greater movement to cover the focusing range than the swing prism type, allowing finer movement and greater accuracy. Another advantage is that the prisms need not be located next to the mirror. Used on the Super Ikonta, 1934, where the prisms were mounted on the front standard, a common wheel moved the lens and the prisms.18
Swing WedgeTwo fixed prisms (or similar) are used. In front of one there are two cylindrical lenses, in the neutral position there is no deflection. By swinging one of the lenses a prism of varying angle is formed. Used on the Contax 11 camera, 1936. Rather than two air-separated mirrors or prisms, Zeiss favoured a solid glass rhomboid.19
Bantam SpecialTwo fixed prisms are used. In front of one, and attached to the front standard, is a lens that moves laterally. As the camera lens is rotated for focusing a cam moves the rangefinder lens parallel to the rangefinder base. A further development of this was to incorporate the lens behind the prism inside the camera housing. The images are considerably magnified by the rangefinder lens, a similar lens in the path of the secondary image and the eyepiece lenses. The Porro prism close to the eyepiece erects the two images. Developed by Joseph Mihalyi.20
Leica M2The M series used a swivelling lens with the movement coupled to rear of the camera lens. The rangefinder and view-finder were combined in a single window, suspended frames were illuminated from a dedicated window.
Split FieldThe two images are displayed one above the other, as the rangefinder is altered one of the images will move. Typically the mirror or prism in front of the eyepiece has part of its surface clear, the rest is silvered to reflect the 'second image'. The field may be split horizontally or just a middle section may be silvered.
Double ImagePart or all of the mirror is semi-silvered giving a double image. Usually the two images are coloured to increase their contrast, this was either by introducing filters or using a different reflective coating to the mirrors.
Rangefinders Built into CamerasThe first coupled rangefinder camera was the 3A Autographic Kodak Special of 1916. It was not until the 1930s, however, that coupled rangefinders became popular, examples are: Agfa Standard, 1930; Roland, 1931; Prominent, 1932; and Leica 11, 1932. A number of cameras were produced with uncoupled rangefinders.
On miniature or solid bodied cameras where the lens is directly attached to the camera body the rangefinder could be coupled to the lens movement by resting a lever, which controlled the rangefinder movement, on the rear of the lens.
References:Lipinski. Westminster Cat. 1939, p. 43.
Early use of magnesium and flash powder was limited to fairly specific circumstances such as a restricted location or where a portable light source was required. The smoke and debris produced, as well as the distraction of the flash, prevented their general use in studios where other light sources were used; ideas to burn the powder within a glass container did not materialise. There were early proposals to synchronise the camera shutter with a magnesium powder flash but usually an 'open flash' was used where the shutter was opened, the flash fired and the shutter closed.21 Greater use was made from the 1890s when amateurs started using the simpler devices coming on the market.22
Magnesium Ribbon HoldersGenerally these consist of a reel of magnesium ribbon or, earlier, wire which can be moved either mechanically or by hand from a container. They date from the 1860s, though little used, fairly elaborate feeds such as clockwork were employed. By the 1900s simple, cheap, devices were being produced. The light produced was continuous, only dependent on the amount of ribbon. Also used in enlarging.
Magnesium PowderThese work by passing magnesium powder through a flame and date from the 1880s. The typical arrangement was to blow, by means of a rubber bulb, powder through a spirit flame producing a flash as opposed to a continuous light. The well-known Todd-Forrett lamp is of this type.23
Flash PowderFlash Powder is magnesium powder mixed with potassium chlorate, unlike pure magnesium powder, flash powder is readily ignited by a spark, flint wheel or by a flame. Although there was some earlier suggestions for using additives with magnesium powder, wide use followed the publication of Gaedicke and Miethe's proposals.24 Available from the 1890s. A variant was to coat a wooden rod with flash powder which was then ignited.
Flash BulbsThe earliest flash bulbs contained aluminium foil in a bulb of low pressure oxygen. Later wire was used in place of foil. Available from the early 1930s.
References:Coe, Cameras has some good information on early equipment.
References & Notes
 The increase was ⅔ that of the thickness of the plate. BP 23738/1907. BJA 1909, p. 647. BJA 1913, p. 119.
 BJA 1901, p. 257.
 Jules Richard, BP 11640/1896. BP 15132/1898.
 J.B. Weber, BP 9103/1894.
 Busch, BP 2359/1907. BJA 1909, p. 554. Sinclair Cat 1910, p. 193.
 Used on the Zeiss Magnar camera of around 1908.
 Early examples are: Thompson Revolver camera, 1862; Marion Academy, 1882; Beck Frena, 1893.
 Voigtländer produced a finder where the field was outlined in white on a black field (Kontur).
 Doyen, BP 18695/1897.
 Stevens, BP 378270/1932.
 Identoscope, BP 11670/1905. T-P, 10269/1907.
 N&G, N&G Cat. 1908, p. 148. Watson, BP 11147/1911. BJA 1908, pp. 724, 994.
 L.M. Berthon, BP 7121/1887.
 N&G Cat. 1908, p. 147.
 There are two forms of this type of rangefinder, the one used on cameras is the 'coincident' type where the two images of the subject are viewed in one finder, one image is moved until the images coincide. In the second form - stereoscopic - the two images are viewed by each eye, the eye/brain fuse the images into one. A graticule is contained in each eyepiece, the rangefinder is altered until the subject and graticule fuse together.
Early proposals were - W. Thorner, BP 22338/1906. Swing mirror type, S.M. Player, BJA 1911, p. 505. Swing mirror type coupled to the lens. P.J. Murray, BP 107213, BJA 1919, p. 266. J. Becker patented a number of ways of coupling the rangefinder with the camera, US 1178474/1916.
 BP 13421/1914. This patent seems to be the basis for the rangefinder fitted to the 3A Autographic Kodak Special of 1916 where the arrangement was simplified by fitting a narrow wedge in place of the lens combination.
H.F. Toennies patented (BP 292602/1927) the arrangement of using two lenses of equal but opposite power as the deflection device. As the lens was focused the negative lens slid linearly relative to the positive lens. The patent also shows the base of the rangefinder consisting of a solid glass rhomboid rather than air-spaced mirrors.
 BP 405208/1934. ZI Cat. 1937, p. 21.
 BP 419915/1934. ZI Cat. 1937, p. 43. Contax Photography, 3rd ed. p. 17.
 BP 454134/1936. US 2113307/1938.
 Slingsby, BP 3571/1890. Hart, BP 2789/89.
 The price of magnesium fell considerably in the mid 1880s which may have increased its use in photography. BJA 1887.
 BP 10482/1891.
 BP 7035/1887.