Single-Lens Reflex Camera
A SLR camera permits the photographer to see exactly what will be
captured, as the translucent screen and the mirror are set up in a way in which
they represent the real image precisely as it will eventually appear on the
film as it is that which is seen through the lens. This is advantageous, as the
design allows one to adjust the focus and it compose the scene in order to get
the desired effect and picture.
This is contrary to viewfinder cameras, as the image captured with these
can often be very different from what was expected and for this reason many
professional photographers tend to use SLR cameras.
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| An illustration of the SLR system |
The camera
works by utilizing a mirror and prism system,
in which a slanted mirror is positioned between the lens and the shutter along
with a piece of translucent glass and a prism above it. A SLR camera
essentially works like a periscope; the lower mirror reflects the real image on
to the translucent glass, which acts as a projection screen. The job of the
prism is therefore to flip the image (so it appears to be the right side up
again) on to the screen and to redirect it on to the viewfinder window. Upon clicking the shutter
button, the mirror is quickly switched out of the way in order to direct the
image on to the exposed film. There exists a shutter-timer system which ensures that the mirror connected to the
system will stay open as long as the shutter itself is open. This explains the
brief blackout to occur when taking a picture.
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| A perspective drawing illustrating the reversal of the image by the prism |
The major
difference between manual and automatic cameras is that with manual models, the
user controls everything, whereas with automatic cameras this is done by the
central microprocessor instead. The central microprocessor controls the several
small motors, which adjust the lens and control the aperture, based on the
information it receives from the auto focus system and the light meter.
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