These are
the most popular camera made.
Although
the Soviet GOMZ sport (1935) was the first 35 mm SLR, it
was the Ihagee Kine-Exakta (1936) that was truly influential,
from here there have been a steady stream of developments
through various classic makes and models.
Easy to use
and now quite cheap, the design was developed to allow a
wide range of screens, lenses,
motor drives, filters and other accessories to be used and
have a most usually have a light meter built in and coupled
to the aperture and shutter controls.
The biggest
advantage of this type of camera is that they allow viewing
through the taking lens and give a precise view of how the
subject is framed and where the exact point of focus is.
The image is projected through the lens onto a mirror where
the image is focused onto a ground glass screen, and from
here onto another series of mirrors to an viewing window.
When the shutter is released the mirror is swung up allowing
the image to project through onto the film.