Talk:Pentaprism

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The image shown (Image:Pentaprism.png) on this article is incorrect. A pentaprism is not a pentagonal prism, but a roof prism with 45 degree diagonal faces meeting at a peak at the top of the shape. This is required to reflect the resulting image laterally to unreverse the reversed image produced on the viewscreen by an SLR camera's reflex mirror. The true shape of a pentaprism can be seen on the photo near the bottom of this page: Pentaprism at Konica Minolta - dmmaus 00:45, 9 Mar 2005 (UTC)


 * A pentaprism is correctly shown in the diagram - it's used in optics, independent of its use in photography. However, the type of pentaprism used in camera viewfinders adds an extra roof section to one of the reflecting sides to give the lateral inversion. It's more properly called a "roof pentaprism" but casual use omits the "roof" part of the name. 128.196.200.115 18:11, 9 Mar 2005 (UTC)


 * I've added additional information about this to the article. It would be nice if someone could provide an image of the SLR "roofed" version. - dmmaus 05:35, 11 Mar 2005 (UTC)

Revert problem
Something has gone wrong when reverting. Appartently I can choose from a version with one contrib or another contrib but not both :-( I'll fix it as ASAP, using the history.
 * Everything is OK now, I hope. We have got all new stuff, ditched the vandalism and still retained the new interwiki-link. Shinobu 13:55, 8 Apr 2005 (UTC)

Is the Roof Pentaprism image correct?
I contribute mainly to the french wikipedia. I tried to translate this article to french (actually only the part concerning the roof pentaprism, and including it directly in an article discussing SLRs). The thing is that a user quickly removed it, stating the picture (as well as the text) is wrong.

Since other wikipedia's in the world use this roof prism picture (or a similar one with the same principle) I doubt this (and it seems quite OK to me anyway), but just to know: is there any other sources on the Internet explaining the way a roof pentaprism works, preferably with some sort of illustration? I made some search and found nothing. --Jérémie A. 12:43, 28 February 2006 (UTC)
 * It's correct, as is easily shown using secondary school level geometry. Shinobu 15:43, 3 March 2006 (UTC)

My understanding was that it was called a Pentaprism because it was invented by the firm of Pentax! I read this in an early book written by Pentax (of course) although at the moment I can't find the book. It would be an interesting citation if I could :-)Johnchapple (talk) 08:45, 3 June 2009 (UTC)

The images seem correct to me. When you look through a single lens reflex camera view window, you are looking through the lens via the roof prism and also via the tilted mirror just in front of the shutter. The mirror just in front of the shutter would show a backwards looking letter the same as a mirror in a bathroom. Therefore, to correct the image, the roof pentaprism switches left and right again to create an accurate representation of a letter placed in front of the lens. Looking through the view window via the pentaprism and the mirror reflecting into the pentaprism shows an accurate normal letter in front of the lens. Therefore, I say that both of the diagram images are correct. — Preceding unsigned comment added by 2601:190:401:C60:C8A1:F3E0:25DA:DCF4 (talk) 01:03, 20 January 2021 (UTC)

the roof
C I can easily believe that such a thing works in theory, but what about in practice? That roof edge is right in the middle of the image. It's not going to be perfectly machined. It sure seems that the camera will have a line down the middle. AlbertCahalan 04:26, 9 April 2006 (UTC)


 * Of course it works in practice - there are millions of practical examples to prove it! Nothing is perfectly machined because perfection is unattainable. However they are made well enough to work. There is a vertical line down the middle, which you may or may not be able to see. If the lighting conditions are just so it can be clearly visible. In my expeience it's easier to see on a roof pentamirror though. 83.104.249.240 (talk) 01:59, 16 March 2009 (UTC)

the image of 2 pentaprisms are incorrect
1) The un-roofed pentaprism that is coated (figure above) will result in an upright and same left-to-right image.

2) The roofed pentaprism (figure below) will result in an upright BUT different left-to-right image —Preceding unsigned comment added by Wibi82 (talk • contribs) 12:08, 6 October 2007 (UTC)

Light beam crossing
Someone must explain why the crossing of the rays doesn't affect the final image. —Preceding unsigned comment added by 79.114.19.68 (talk) 10:01, 1 May 2008 (UTC)
 * Light crosses all the time in the world without issue.Hustvedt (talk) 06:20, 21 January 2009 (UTC)

Too many Pictures?
I added an example picture of the projection a roof pentaprism does, but I think this article might have too many pictures now. I like the Nikon F picture because the pentaprism hump is very obvious, and don't like the Contax and Bronica pictures since they are more about the pentaprism housing.Hustvedt (talk) 06:20, 21 January 2009 (UTC)


 * The Bronica prism would be more useful if it were flipped over to show the optical surface. As it stands the picture is rather pointless. Only one of either the Nikon or the Contax pictures is needed. Having both adds nothing. If the consensus is that the Nikon picture is the more appropriate, perhaps another picture of the same camera with the prism removed but included in the picture would add a little. 83.104.249.240 (talk) 02:07, 16 March 2009 (UTC)

What are the angles between each intersecting face?
A diagram showing this would be very useful. Hamsterlopithecus (talk) 17:14, 4 July 2013 (UTC)