One function of an optical viewfinder is to view and arrange images that need to be recorded on film, and secondly, to allow the image to be focused while viewing. These functions cannot be accomplished without the use of an optical lens, and this article will describe the optical viewfinder in detail.
What is the function of the optical viewfinder?
Before taking each picture one always wonders: what does the image on the camera look like? The process of looking through the viewfinder and realizing the shot can sometimes be a long one, with a lot of fumbling and fumbling before the shutter is pressed with a satisfactory prediction of the composition.
This is the first function of the optical viewfinder: to view and arrange the image on the film to be recorded.
The viewfinder has a second function: to allow the image to be focused while it is being viewed. Often, the viewfinder system and the focusing system are combined into one. Therefore, when describing the various viewfinder systems below, the various focusing systems used will also be covered. The main types of framing systems are listed below:
(1) optical viewfinder
(2) single-lens reflex viewfinder (SLR viewfinder)
(3) dual-lens reflex viewfinder
(4) Hair glass back
(5) Electronic video viewfinder
About optical viewfinders and rangefinders
Optical viewfinders seem to be more niche at a time when microlenses are so prevalent, and in fact, for decades everyone viewed the subject through a glass window oriented in the same direction as the lens. Early digital cameras were equipped with this simple system, both at the mid-range and high-end.
Although this system is simple, it inevitably has the limitation of not being able to focus directly through the viewfinder. The image seen in the viewfinder is always clear because of the simple peek through the glass window. Other methods must be used to focus the image that reaches the film.
Different types of cameras solve this problem in three different ways, mainly:
1. Fixed focus
2. rangefinder focusing
3. automatic focusing
(1) Fixed Focus
The fixed focus system guides the photographer to aim and shoot so that, for example, everything 4 feet away is clear, while the actual recorded image is blurry. It would still be quite good to shoot anything within 4 feet, which is a system limitation.
For more specialized and creative control of the image, more precise systems are needed, which is why more advanced cameras either use rangefinder focusing or autofocus.
(2) Rangefinder Focus
Cameras equipped with rangefinders existed more than half a century ago. Rangefinders were the basic focusing device used in most early 35mm cameras and are still used in the Leica M series cameras. A combination of a reflector and linkage is used in rangefinder cameras to connect the image that reaches the film with the image seen in the viewfinder.
If the image on the film is blurry, then the image seen in the viewfinder window is also defective. Often the image is either ghostly, similar to a ghost theater on a television screen, or the center of the image is split. Therefore, it was known that as long as the image seen from the viewfinder was defective, then the image recorded on the film would also be blurry. As the lens barrel is turned, the image can be seen to become clearer and sharper, and one knows that the image recorded on the film is also clear.
Another problem, such as photographing a stamp at very close range and seeing from the viewfinder that you've got the stamp in the center, only to get the final photo and find that only half of the stamp has been captured in the frame, with the rest of it moving out of the frame, is a phenomenon known as parallax.
To summarize, rangefinder systems have certain limitations, knowing the emergence of single-lens reflex systems.
The heart of the SLR system is a moving reflector. It is placed at a 45-degree angle in front of the film plane. The light from the lens is reflected upward from the reflector onto the hair glass. With early SLR cameras, the image on the hair glass, although upright, was reversed from left to right. To correct this defect, eye-level SLR cameras were fitted with a five-sided prism (pentaprism) above the hair glass. This prism reflects the image several times until it is sent to the eyepiece, at which point the image is upright and corrected.
Pentaprism is a reflective device for DSLR framing, which serves to correct the left-right reversed image on the focusing screen so that the image seen in framing is the same as the orientation of the scene seen directly.
However, not all photographers use SLR cameras, probably for two reasons.
First, there is the respect for tradition; SLR framing is a form of optical framing, just in a different way. The Leica optical viewfinder is usually placed above the lens, and the image seen from the optical viewfinder is different from the image projected by the lens onto the sensor, in short-range shooting, a typical optical viewfinder will only allow the user to see 80-90% of the actual coverage of the lens.
Bright images can still be seen in the Leica optical viewfinder in weak lighting conditions. Compared to the SLR, the image seen in the SLR viewfinder is much darker under equal lighting conditions.
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