> > Hi Karen, > > > > In the specifications it indicates that the AF working range > for the EOS-3, > > 1V, and 1D is EV 0-18. The EOS D30 is EV 2 - 18. > > I believe this would indicate that the AF can focus throughout the same > > ranges up to and including F8 except for the D30 which is EV 2 > - 18 which > > may point to F5.6 min aperture for AF with that model. > > > > Peter K > > Peter, > > I don't believe the actual light level has anything to do with focusing > ability at f/8...the reason it won't focus at f/8 even in full sunlight > is that it needs to (effectively) look out of the two opposite sides of > the lens so that it can compare the phase shift between these two areas > of the lens...just like a rangefinder...f/8 doesn't allow the "base" of > the "rangefinder" to be wide enough to achieve any precision unless it > uses the higher quality Eos3/1v sensor. The argument that the increased > magnification affects the effective depth of field level and requires > higher precision seems to be the only likely reason that the 1D couldn't > AF at f/8, unless for some reason they just used a less sensitive sensor > in the 1D. Personally I am guessing (hoping) it will AF at f/8, but > we'll have to wait and see. > > That said, yes, I do realize that brightness of the light affects AF > performance, but it isn't the same as the f number limit. > > Mike >
Hi Mike, This is what I posted earlier. If the AF box is the same for all three bodies, EOS 3, EOS 1v EOS 1d and the control logic is limited in the same way, the fact that the image sensor is smaller then a the 35mm film area and causes an effective image magnification of 1.3 controls the limiting AF factors. The existing AF system cannot get enough baseline differential to predictably focus the lens within the acceptable level of error given the DOF requirements of a lens. But as I also mentioned there is no reason for this to be the lower limit if Canon was creative and used real-time analysis of the area sensor to create a much larger baseline. This is the same technique that is used to combine the data from a multi-dish or telescope array to effectively get a much larger more sensitive instrument. Or canon could simply bite the bullet and use a bigger sensor array. Regards, Chip Louie * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
