Hi Vesa, > Has anyone noticed that their EOS-3/1V focuses behind or > in front of the subject with certain focal lengths (here > e.g. 300mm) and/or with certain lens speeds (here f4 vs. > f5.6 max apertures)?
> I know (think) EOS-3 has better AF at f4 when the center > AF sensor is used but I'm not sure if the AF accuracy is > affected (by cross-sensor vs. vertical sensor). The EOS 3 will indeed focus better at f/4 (the maximum aperture of the 200/2.8 lens with 1.4x extender. Better means not only 'quicker' but also 'more accurate'. With the EOS-3, which has such a sensitive AF-sensor, the focussing accuracy is actually limited by the maximum aperture of the lens used. For a camera's AF-system 'everything within the DOF is sharp'. So the maximum focussing accuracy is about equal to the DOF. With f/4 the DOF is about 50% less than the depth-of-focus of the f/5.6 lens (your 100-400 mm zoom). So the focussing accuracy with your 200+1.4 extender lens combo is about 50% higher. In the case where the DOF with your 200mm+extender lens is, say, 10 cm the DOF with your zoom will be about 15 cm. So the EOS-3 with 200+extender will focus somewhere within the 10 cm range. The EOS-3 with zoom will focus somewhere in the 15 cm range. Maybe this is the reason you find that the EOS-3 will focus less acurate with the zoom attached. Hope this helps, kind regards, Bart * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
