AlanF said:
mb66energy said:
[...]
With a 5D classic I see losses of detail from f/8 on while doing macro shots at 1:3 (I think it
is actually comparable to f/11). From that I extrapolate that the 5Ds can be used at a
max aperture of f/5.6 to use the lenses capabilities in similar situations. The lens used was
the near ideal EF 2.8 100mm Macro (non-L).
To use the full potential of the 5Ds you need stacking at least for macro but I think it will
be necessary for landscape and architecture as well.
Is that a valid extrapolation? Go to the slrgear site where they measure IQ at different apertures for both full frame and crop. For all the good lenses, there is minimal diffraction degradation at f/8, a tiny amount at f/11, and then more significant at f/16. It is exactly the same for FF and the 7D with 5Ds size pixels.
I think it is a valid extrapolation. Look at the plot of the resolution @ photozone
http://www.photozone.de/canon_eos_ff/508-zeiss100f2eosff?start=1
http://www.photozone.de/canon_eos_ff/847-canon35f2isff?start=1
http://www.photozone.de/canon_eos_ff/430-canon_135_2_5d?start=1
and
http://www.photozone.de/canon_eos_ff/489-canon_100_28_5d?start=1
The sharpness loss with higher f-numbers is less dramatic if you take the suppressed zero into account.
or compare the 2.8 100 L macro @ f/4 and f/16 with the 7D ii (you are right to use that camera as a good extrapolation basis for 5Ds):
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=674&Camera=963&Sample=0&FLI=0&API=2&LensComp=674&CameraComp=963&SampleComp=0&FLIComp=0&APIComp=6
Less pronounced with the 1Ds iii:
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=674&Camera=453&Sample=0&FLI=0&API=2&LensComp=674&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=6
With very good lenses you can spot the decrease of center sharpness from f/4 on on a 20 MPix sensor consistently (in the graphs of photozone). The corner quality increases usually while closing one or two f-stops due to the minimization of lens errors.
With better sensors you will get more detailed images but if you stop down to f/16 you will loose a lot of this gain and I think it will start with f/5.6 or f/8 if "detailedness" is a strong concern.
And never underestimate the sensitivity of our eye-brain system which detects a 5% or 10% loss in detail easily - I do it very often too
But I am open to update my understanding while the new data is coming in!