Porro prism binoculars have an offset prism design that 'bends' the incoming image before it reaches the user's eye. This 'bending' lets the binocular deliver great image quality, including increased image depth and a more lifelike, three-dimensional image, but because of the more complex path the light must take, the binoculars are usually a little bit bigger than roof prism models.
acess: http://www.nikonsportoptics.com/glossary.php for more explanations
The illustration and discussion of the double porro prism contradicts the first section. If a single porro prism rotates an image 180 then a double must rotate it 360. (Which is why it is used in binoculars, which have "normal" images.) And the middle F in the double prism image is not rotated but reflected. Therefore, I deleted the text on double porro prisms. -- etune
I have restored the deleted text, since the reasoning above is erroneous. The middle F is rotated when considered wrt the direction of the input and output beams. 126.96.36.199 19:56, 23 December 2006 (UTC)
It seems to me that double prism discussion erroneously states that the handedness is unchanged, if it is speaking to the original image. Schreca (talk)schreca —Preceding undated comment added 13:55, 5 August 2010 (UTC).