Converting Used Canon FD lenses for E420

Besides the advantage of shooting in lower light, or shooting at a lower ISO in the same light, a large aperture gives you shallower depth of field for subject isolation or bluring the background.  But soetimes shallow DoF is a liability- for moving subject which might not stay in focus, for macro where DoF may be razor thin anyway, and even for portrature you might not want just one eyelash in focus... But then, a given apeture on 4/3 will give greater DoF than on FF.

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Art P
"I am a creature of contrast,
of light and shadow.
I live where the two play together,
I thrive on the conflict"