article no 01> SINGLE- LENSE REFLEX CAMERA. ( SLR camera )

Single lens reflex cameras are very popular among amateurs and as well as professionals. In these kind of cameras, typically uses a mirror and prism system (hence "reflex", from the mirror's reflection) that permits the photographer to view through the lens and see exactly what will be captured, contrary to viewfinder cameras where the image could be significantly different from what will be captured.

 The light from the object reflects from a mirror and is taken through the eyepiece to the eye of the photographer (in contrast to a viewfinder camera where the photographer is looking through a separate lens at the subject)

 

The advantage of the SLR is that the eye sees approximately what the film will record, so that you can freely interchange lenses, use close-up lenses, etc. and still see what you will record on the film(or sensor).

THE ANATOMY OF A SLR

To properly answer "what is a digital SLR?" we have to understand a bit about the mechanics of an SLR camera.

In order to avoid getting overly technical we better have a look on this simplified diagram. key elements are highlighted in colors. Those interested in the minute details can read about SLRs on Wikipedia.

01) Light passes through the lens and strikes a mirror (blue).

02) The mirror reflects the light up to a focusing screen.

03)Light passes through the focusing screen and enters a block of glass called

    a pentaprism (or pentamirror)(purple).

04)The pentaprism reflects the image so that you can see it in the viewfinder.

05)When we take a photo, the mirror flips up and a shutter opens that exposes the digital      sensor (green) to light.

Light, which comes both horizontally and vertically inverted after passing through the lens, is reflected upwards by the reflex mirror, into the pentaprism where it is reflected several times to correct the inversions caused by the lens, and align the images with the viewfinder.

We can have a look at the diagram below to understand the main idea of what we are talking now, and also other parts which have included in the diagram will help us to study the other mechanisms in a DSLR.

This is a great example of what-you-see-is-what-you-get. By using the viewfinder you can precisely compose your image and adjust the focus.

Is the image that you see in the viewfinder 100% accurate? In most cases it isn't. If you read digital SLR camera reviews, you may hear a lot about viewfinder "coverage" and "brightness".

Many digital SLR viewfinders only show you 95% of the image that will be captured by the sensor - this is what "coverage" refers to. For examples.., most of entry level and mid-range cameras such as Nikon d3100, Nikon d 3200, Nikon d 5100, Nikon d 5200.

But almost every pro DSLRs (Nikon Ds) and some mid-range cameras(Nikon D7100)  gives 100% viewfinder coverage.

But the thing is unless we are extremely precise when it comes to our photographs we won't notice the 5% difference.

Digital SLR viewfinders also vary in brightness,(by the way, pentaprism viewfinders are brighter than pentamirrors. We will talk on that later. ;) ) which is another way of saying how clear the image appears. "Bright" viewfinders make it easier to use manual focus, since you can clearly see the details of your subject.

The diagrams below shows that the light is bounced from a mirror through a pentaprism (or pentamirror) to the viewer’s eye while choosing the object for capture.

 Now the question is what happen to the mirror when the image is captured.., Of course.., when the shutter released it lifts the viewing mirror while open the shutter to allow the light to fall on to the film (or sensor).

Generallythere are some common benefits when we use a SLR camera.

  With an SLR camera, the photographer see exactly what the lens sees.

  In most of SLRs, photographer can change the lens on the camera.

  Usually SLRs (Film or Digital) have large image sensors

    (or films) that produce high-quality photos.

  An SLR has a near-zero lag time, and is ideal for action photography.

This is just a simplified article.., If you need further details.., you better search for it. These links below might be useful.

sources, 

http://en.wikipedia.org/wiki/Single-lens_reflex_camera

http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/slr.html

http://www.digital-slr-guide.com/what-is-a-digital-slr.html

http://alphatracks.com/images/reflex.jpg
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/imggo/slr2.gif
http://www.dptips-central.com/image-files/slr_camera.gif
http://www.dallasartsrevue.com/resources/photographingArt/SLR-lens-mirror-penta.jpg