I'm looking at the specs for the olympus 4/3 macro lenses on B&H. Under magnification, for the 50mm f/2.0 macro, it states:
1:2 (1:1 35mm equivalent)
So, what does it mean to have a 1:1 in 35mm equvalent?
What they mean is that the smallest subject size with which you can fill the frame is as with a 1:1 macro in 35mm format. To be precise, 1:2 in 4/3 fills the frame with a subject about 26x35mm, whereas 1:1 in 35mm fills the frame with a subject 24x36mm.
But the 4/3 macro lens I like most is the new, cheaper 35/3.5 1:1 macro, which can fill the 8MP frame of an E-500 with a tiny 13x17.3mm field. Smaller pixels have their advantages for us bug photography fans!