The Canon EF 70-210 f4 is a fairly old Canon AF lens and as such was obviously designed for film, but I’ve found it performs pretty well with my Canon EOS 20D. Performance with the Canon EOS 5D isn’t as good at wider apertures, and, as with almost all lenses used wide open with the Canon EOS 5D there is a fair amount of vignetting - with the EF 70-210 f4 it’s most obvious at the longer end of the zoom range. Other than that results are OK to good in the center of the field at all focal lengths but there is a fair amount of softness in the corners especially at 70mm where corners are very soft at full aperture. At f5.6 corner performance at 70mm is still the lens’s biggest weakness. Throughout the rest of the zoom range even corner performance is very good to excellent.
Stopped down to f8 or f11 this lens produces surprisingly good results with the Canon EOS 5D, and although the focusing may be slow and relatively noisy by present Canon standards, it does seem accurate and if you can live with the old style push / pull zooming action this is a far better lens than many modern lightweight plastic tele zooms available for much the same money as this can be found for ebay. If you can’t quite justify the cost of the present Canon 70-210 f4L this is a good option for the 5D or 20D.