A Look at Viewfinders
A lot of cameras from the past had some kind of rectangular frame to indicate the approximate size and position of the image that was captured by the lens of the camera. The frame finder was usually the only wire that was bent. The drawback of an uncomplicated frame finder is that it could be highly inaccurate. What you see will vary based on the distance and angle at which you look through it.
Finders of sport
Frame finders with more sophisticated features consisted of two frames: one smaller to the eye and a larger one that is further away. The user must be able to see the image that is to be taken by placing it on the more petite frame in the larger frame, and the larger rectangle offers an indication of what is likely to be in the photo. It is easy to use and offers excellent visibility along the edge of the frame. It also lets the image be seen at natural size. The sports finder works well for press-related applications as well as following fast-moving actions, but it is not very accurate. The issue that sports finders bring up has to do with the fact that the frame behind (ocular) isn’t in view when an eye’s focus is set to view distant objects. But, optical viewfinders in the past produced a small image, making it difficult to manipulate when the scene contained motion. Sports finders were efficient enough to be used on certain kinds of cameras up to the present (e.g. modern underwater cameras).
The stunning finder included an angled mirror with 45 degrees with two lenses that are positioned 90 degrees from each other. These finders are generally tiny (about 1 centimetre wide) and can be seen from above and present an image that’s reversed left to right, which makes them hard to operate. But, they were widespread.
A specific version of Brilliant Finder, which was called the Sellar finder, was made only of a concave lens that had a targeting aid to aid the user in positioning their eye in order to get the best perspective.
The frame/sports finder was called the Newton finder. It has one negative (Plano-concaved) lens inside the frame in front, as well as an instrument for targeting close to the user’s eyes. The negative lens decreases the dimension of the scene by allowing for the scene’s front view to becoming smaller (but it is difficult for those who have longsighted eyes to make use of the lens).
Although still containing the same set of frames projected onto the lens of the camera, the telescopic viewfinders incorporated an inverse lens at the front and an erect lens for the eyepiece. This is a reverse of Galileo’s telescope and is often referred to as”the reverse” Galilean viewfinder. Similar to the Newton finder, they provide an image that is smaller in size.
This version is a reverse Galilean finder that features an unfinished rear face attached that is affixed to the front lens, which displays an image of frames drawn around the perimeter of the lens. The user is able to see the frames overlayed in the background (creating illusions that the lines are farther away). The camera’s design began to incorporate viewfinders into the camera’s body. However, the system didn’t perform as well, leading to the creation of the frame finder that is bright.
Bright frame finders
In this method, the frame of bright light is presented in a telescopic finder by putting a half-silvered mirror within the viewfinder, at an angle that allows it to reflect frames on the side and illuminated by light coming from a transparent panel located on the camera’s front (often located near an optical viewfinder).
Keplerian viewfinders make use of the reversed Kepler telescope. To simplify explanations, the Keplerian viewfinder can be described as an (optical) improvement over the Galilean telescope, which creates an image that is upside down. In viewfinders designed for cameras, there is a prism that can reverse the image to ensure it can be seen from the opposite direction up. This lets the path of lighting becomes folded (like when you use a pair of binoculars), which results in an image finder that fits the space available in the camera (as is the case with the Canon Demi). The brightness and clarity of the Keplerian finder are also improved in the same manner binoculars can improve the basic telescope.
Parallax mistakes and their correction
Parallax errors occur whenever an object has to be observed from two different lines of vision, as when the viewfinder must be in a different direction from the lens of the camera (usually over and usually to either side). The amount of error is dependent upon the distance. It’s not significant for distant scenes. However, it is significant when close-up objects are in focus that can cause incorrect framing.
Correction of parallax errors in telescopic viewfinders is done in a variety of methods. The most basic is to use a second frame-lines that are part of the bright-line finder, which indicate the boundaries of the area that will be captured when it is in close focus. A more sophisticated approach is to make the bright lines of the finder can be adjusted mechanically (reposition) to match the camera lens’s adjustment of focus. Another option was to create an instrument that could adjust an angle for a telescopic locater (this was not a common practice).
Ground glass screens
This piece would not have been complete without a brief mention of ground glass screens. These screens also serve as viewfinders.
In reflex cameras where the subject is seen by a mirror. It reflects the light from the lens onto a ground-glass focusing screen. The main difference between the single-lens reflex (SLR) and twin-lens reflex (TLR) is that in an SLR camera, the mirror is moved prior to the exposure (to let the light be focused onto the film); however, in the TLR camera, the mirror, as well as the screen for focusing, are set up as a viewfinder. The image is taken using the twin lens.
The most basic screen is seen from above. This is referred to as a waist-level finder. The view on the finders is reversed left-to-right. Fresnel lenses (made from a series of concentric rings designed to disperse light) is typically placed over the screen used to focus, to increase the brightness of the screen’s corners.
This method was a viewfinder made of ground glass was utilized in the very first wet plate cameras, however, without mirrors.
In the latest SLR cameras, light is reflected through a pentaprism, which provides an eye-level viewfinder. The pentaprism does not just alter the path of lighting, but it additionally alters the image so that it can be seen in the correct direction. Pentaprisms do not suffer from errors in parallax because they are viewed and captured by identical lenses.