Neither of you apparantly understand that the shooting aperture has nothing to do with the focus accuracy.
f4 might get everything reasonably sharp at 17mm on 135mm / leica / minature format DSLR's, but won't get you far anywhere else unless eveything in your scene is on the same focus plane.
The advice is useless, tosh. My biggest gripe is that somebody would actually read it and try it and miss out on important shots. Might as well have said get a lens with hyperfocal scales and shooting everything at f11. It's got about as much to do with how AF works. Jaysus.
Unless of course you meant that we should all buy lenses no faster than f4 so we can give our AF systems a chance for point and recompose. Or try just not using it
I stand by it lads.
i dont disagree with your technical assessment of either of your posts....but none of that has anything to do with what Neuro and I are suggesting to the OP.
to be clear, if AF accuracy is the desired result coupled with the focus and recompose technique then what i am advising to the OP is buying the 5D3 would be a better option for him using his existing lens lineup and using the improved responsiveness of the 5D3's outer points when composing RATHER than buying 2.8 zooms and continuing to do focus and recompose.
yes, buying 2.8 zooms offers better AF on the 5D2...but any accuracy gained is wasted on the focus and recompose technique as the very simple physics of the technique circumvent the accuracy of the original focus acquisition...unless of course your are shooting at F4 and above with the extra depth of field that would compensate for the discrepancies introduced with the recomposition. at this point....a wiser recommendation would to be just buy the 5D3 to take advantage of better, more accurate focus points outside of the center point and ditch focus and recompose.
this is sound advice...which does not ignore your completely valid points about how AF systems work coupled with different lenses capable of different maximum apertures. your posts do ignore however the very real problems the focus and recompose technique introduces to focus accuracy....especially at apertures greater than F4. the OP should be made aware of this to help inform him of his decision.
i appreciate your enthusiastic points...but you are arguing something that 1. i dont disagree with and 2. doesnt have anything to do with the actual point that i am discussing.