Why do SLRs use a pentaprism instead of a mirror?

devilfunhousedevilfunhouse
in Consumer Electronics

I've done some research, but no one explains this. The combination of the mirror in front of the sensor/film and another mirror in the upper half of the body should correct the orientation/handedness of the image, no? And it would take up less space?

Comments

  • eclipseeclipse

    Actually the image would still be reversed, left to right in such a pure configuration and unless you are forgetting about the focusing screen, you'd also end up with an image that's out of focus relative to the film/sensor plane. The distance from the main mirror to the focusing screen below the pentaprism/pentamirror and the distance from that mirror to the film/sensor plane are identical. If we have a straight mirror configuration, and focus until the image appears in focus to your eye rather than the film plane, the recorded image will not be in focus. Take a look at the Wikipedia article below:

    http://en.wikipedia.org/wiki/Pentaprism

  • the-beaver-for-presidentthe-beaver-for-president

    The image is upside down and backwards when it comes out of the lens, the mirror and pentaprism corrects this for your viewing pleasure. Check out the ground glass of a view camera or the viewfinder on a TLR and you'll see what's going on.

  • paul-r-dipping-my-toe-back-inpaul-r-dipping-my-toe-back-in

    And where would the meter go in this very pure but simple optical path?

  • bethany-robertson_60bdff43835e8bethany-robertson_60bdff43835e8

    Cost is the usual reason.

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