Editing Single-lens reflex camera (section)

== Optical components ==
[[File:R-DSC08774-WMC.jpg|thumb|upright=1.13|Focusing screen on Praktica Super TL1000]]
[[File:SLR cross section.svg|thumb|upright=1.13|Cross-section view of SLR system:
1: Front-mount lens (four-element Tessar design)
2: Reflex mirror at 45-degree angle
3: Focal plane shutter
4: Film or sensor
5: Reflex mirror in the up position
6: [[Focusing screen]]
7: Optical glass pentaprism (or pentamirror)
8: Eyepiece (can have diopter correction ability)]]

A cross-section (''or'' 'side-view') of the optical components of a typical SLR camera shows how the light passes through the lens assembly, is reflected by the mirror placed at a 45-degree angle, and is projected on the matte [[focusing screen]]. Via a condensing lens and internal reflections in the roof pentaprism the image appears in the eyepiece. When an image is taken, the mirror moves upwards from its resting position in the direction of the arrow, the focal plane shutter opens, and the image is projected onto the [[photographic film|film]] or [[Charge-coupled device|sensor]] in exactly the same manner as on the focusing screen.

This feature distinguishes SLRs from other cameras as the photographer sees the image composed exactly as it will be captured on the film or [[Charge-coupled device|sensor]].

[[File:SLR Pentaprism.svg|thumb|upright=1.13|A perspective drawing showing how a roof pentaprism corrects a laterally reversed SLR image]]

Most 35&nbsp;mm SLRs use a roof [[pentaprism]] or penta-mirror to direct the light to the eyepiece, first used on the 1948 [[Duflex]]<ref>{{cite web|url=http://bichkov.com/photopedia/index.php?title=SLR_Camera |title=Article at Photopedia |publisher=Bichkov.com |date=2008-01-23 |access-date=2013-10-15}}</ref> constructed by [[Jenő Dulovits]] and patented August 1943 (Hungary). With this camera also appeared the first [[instant-return mirror]].
The first Japanese pentaprism SLR was the 1955 [[Miranda T (camera)|Miranda T]], followed by the Asahi Pentax, Minolta SR-2, Zunow, Nikon F and the [[Yashica]] Pentamatic. Some SLRs offered removable pentaprisms with optional viewfinder capabilities, such as the [[waist-level finder]], the interchangeable sports finders used on the Canon F1 and F1n; the [[Nikon]] F, F2, F3, F4 and F5; and the Pentax LX.

Another prism design was the [[porro prism]] system used in the [[Olympus Pen F]], the Pen FT, the Pen FV half-frame 35&nbsp;mm SLR cameras. This was later used on the [[Olympus E-300|Olympus EVOLT E-3x0]] series, the [[Leica Camera|Leica]] Digilux 3 and the [[Panasonic Lumix DMC-L1|Panasonic DMC-L1]].

A right-angle finder is available that slips onto the eyepiece of most SLRs and D-SLRs and allows viewing through a waist-level viewfinder. There is also a finder that provides EVF remote capability.