Most of the modern 35mm (small format) and medium format are all of this type. A mirror in the camera body is pivoted at an angle of 450 just in front of the focal plane shutter. The light rays passing through it are reflected above to the focusing screen. The focused image on this screen is seen again through a prism placed at the top. The prism is called ‘Penta Prism’ since it has 5 sides and it turns the light rays to 900 to the viewfinder without reversing the image. The light rays take a total internal reflection inside the prism.
The stop value (f) or aperture is set before the exposure is made. When the shutter is released the deviating mirror is automatically swung up above and the focal plane shutter mounted directly in front of the film, momentarily exposes the film
*** Diagrams visible at www.howstuffworks.com
1 comment:
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