I went through this same issue about 2 months ago. I purchased a non-IS canon 300mm f2.8 through Adorama. The price was right but the lens was not. It's focus ability was hit or miss on my 40d and my 1D. I returned it without difficulty (Adorama was great) and am reassessing my need for a longer telephoto vs. lighting equipment. If I buy again it will be a newer better condition 300mm f.28 IS lens.