Nikon and Canon are the biggest names in DSLR cameras and have the greatest selection of lenses.

Which is best?
Nikon owners say Nikon.
Canon owners say Canon.
This argument has been going on for over 50 years.

The Olympus DSLR lenses (Zuiko) are Olympus lenses.
Olympus started as a lens manufacturing company.
They make excellent lenses.
http://www.star.ucl.ac.uk/~rwesson/esif/om-sif/camhistory/camhistory.htm

I suggest you start by looking at the:

Canon 20D
Nikon D200

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