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The History of the Camera Viewfinder (& 35mm viewfinder cameras)
Early cameras lacked any form of independent viewfinder. Images were composed by means of a ground glass focusing screen, upon which the image was observed. This screen sat in the same position as a film plate, and the two were swapped once the photographer was ready to take a picture. These plate cameras were big, heavy, and rarely used outside of a studio. When roll film became commonly available, cameras gained improved portability, captured new subjects, and needed a quicker and more convenient method of targeting and previewing. The first types of viewfinders were
frame, and early cameras (say those pre the 1940s) often had both options. These devices largely pre-date the popularity of 35mm film format.
Dating to the early 1900s, the Watson finder combined a lens with a mirror at a 45-degree angle, reflecting on to a matte screen at 90 degrees to the lens. The image was upright but reversed left to right, small, dim and difficult to see.
A variation was the Sellar finder, which consisted of a concaved mirror (which reduces the size of the reflected image).
In around 1910, the Watson finder gave way to the Brilliant finder, which replaced the Watson's matte screen with a second lens. This produced a brighter image (hence the name), and became the standard viewfinder up until the 1930s. The down-side of these finders was they produced a very small image (like a tiny screen, usually no more than 1cm across), which was viewed from some distance (e.g. waist or chest level).
Reflective finders were primarily geared towards
finding rather than
viewing the subject.
Conversely, the frame finder was orientated more towards
finding the subject; it's easy to appreciate why cameras often had both types of finder.
Early frame finders comprised nothing more than a bent wire frame, which approximated the position, shape and area captured by the camera's objective lens. The user simply observed their subject through this frame. Although the frame provided a life-size view, with good peripheral vision, the big disadvantage of such a simple device is that it can be a very inaccurate targeting system: what you see varies according to the angle and distance at which you peer through it.
The more sophisticated Sports finder consisted of two frames; a smaller one nearer the eye and a larger one further away. The larger rectangle (or square) gives an indication of what would be included in the shot. The smaller frame was a positioning aid. The user has to sight the image by centring the smaller frame within the larger one, a bit like a gun sight. It was an improvement, but still only moderately accurate. A further problem was that the rear frame becomes out of focus when the eye is adjusted for distant subjects. The system was fast to use, and the two smaller frames could usually be collapsed (folded), making the device compact. The sports finder was so named due to its capacity to more easily follow fast action: the introduction of faster films fuelled a growing interest in action photography. Despite its simplicity and shortcomings, the sports finder was good enough to remain in production on some types of camera until more recent times (e.g. modern underwater cameras).
The 'modern' viewfinder
The introduction of direct vision optical finders created the modern viewfinder camera. The first commercially successful 35mm camera to feature a direct vision optical finder was possibly the 1934 Kodak Retina I. Ironically, today we define viewfinder cameras as being those lacking any form of focusing device, and so relegate their merit, however, many of the late 50s/early 60s models were very well made precision instruments, and aimed at the serious amateur photographer. It was only when affordable cameras with focusing systems became popular (those with integral rangefinders and the SLR) that the audience for viewfinder cameras changed, and their design embraced a simpler snap-shot usage ethos.
The Newton viewfinder (based on the Newtonian telescope) was a development of the sports finder, and had a single negative (plano-concaved) lens in the front frame, and a glazed peep-sight near the user's eye. The negative lens reduces the size of the scene viewed, allowing the front frame to be smaller, and the eye to focus near to the lens. Despite its advantages, the Newton finder presented a very small image, and the near focus was difficult for users with imperfect vision. It appears that early viewfinders were kept deliberately small because their field of view changes as you move your eye across the eyepiece, so their small diameters discouraged mis-sighting. It is often stated that the Newton finder fell from usage in about 1930, but I don't believe that's true: it was much later.
An improved system was the Galilean viewfinder which adds a weak positive lens (convexed) to the rear frame. This arrangement is a reversal of Galileo's telescope, and therefore sometimes called the reverse Galilean viewfinder. The positive eyepiece lens provided major advantages; it enlarged the image of the negative lens, and allowed the eye to focus at infinity. The necessarily close viewing proximity improved sighting accuracy by introducing an optically fixed eye point.
The reverse Galilean viewfinder provided an improved
viewing AND finding facility, and is little changed today.
In researching this topic, I have found very little information that identifies whether particular models had Newtonian or Galilean finders (and there seems to be a naive and universal presumption that any reverse telescope finder was Galilean). The only cameras I've identified with specifically declared Newton finders (in advertising) are the 1951 Agfa Ventura 66 Deluxe, and the 1956 Praktina FX (an SLR with an additional direct vision viewfinder for
fast action and available light photography). The viewfinders of these cameras are very typical of most early 1950s cameras. Their front optic is small, and the rear even smaller - like a peep-hole. They are very different to viewfinders of the late 1950s onwards, when optics got much bigger ... especially the rear optic, which ceased to resemble a peep-hole. These later finders are the Galileans. The earlier versions are likely to be Newtonian.
The Albada finder was developed in 1932, but became popular during the late 1950s. Like many other optical systems, the Albada was not invented specifically for use in cameras, and took some time to find its way into their designs. The Albada is a development of the reverse Galilean finder where a half-silvered rear face to the front lens reflects an image of a set of frame-lines, painted around the surround of the eyepiece lens. The user sees the frame-lines superimposed upon the scene (creating an illusion that the frame-lines are further away and so they appear in-focus). The total field of view is usually larger than that of the objective lens, which gives the user the ability to see moving objects outside the frame-lines. A further benefit of the Albada was that frame-lines could be supplemented by additional markings for close-up shots, and thereby guide effective parallax compensation. In simple Galilean (and Newtonian) finders, frame lines were unsatisfactory because they could not be in clear focus. The Albada finder is sometimes alternatively known as the Bright-line finder, which unfortunately invites confusion with the Bright-frame finder.
The Bright frame finder was a new method for presenting a sharply focused and illuminated sighting frame. It was developed for military use in WWII. The innovation found its way into the 1947 Argus Model 21 where it was called the
Markfinder. The bright frame finder has a half-silvered mirror placed at an angle in the viewfinder line of sight, which projects frame-lines lit through their own light collecting window (often placed next to the viewfinder window/objective). In addition to providing a brightened view, the projected frame-lines improved framing accuracy, since their apparent position is not affected by an off-the-axis user line of sight. As with the Albada finder, the frame-lines appear to be further away than they really are. Although more commonly found on rangefinder cameras, the pioneering Argus Model 21 was a viewfinder. Bright frame finders had become very common by the early 1960s, but never completely replaced the Albada finder.
In 1951, Voigtlander introduced the Kontur; an accessory shoe-mounted supplementary viewfinder. It is used with both eyes open. You look through the Kontur finder with one eye and keep the other open. The Kontur creates an optical illusion, so that what you see is a set of white frame lines projected onto the view of the subject seen by the unobstructed eye. This finder had the benefit of showing virtually unlimited peripheral vision. It works BRILLIANTLY, but amounted to no more than a blip in viewfinder evolution.
Keplerian viewfinders are found in some later compact cameras. For want of a simple explanation, this is a variation on the reverse Kepler telescope, which produces a wider field of view and uses a prism to reverse an otherwise upside-down image. Not only does it produce a bright image using very small optics, but the prism allows the path of the light to be folded (like in a set of binoculars) leading to a viewfinder that can be bent and squeezed into a tiny space (as found in the diminutive Canon Demi or Kowa SW).
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