Return of Interesting article on DxO about 5D III and D800...

Started Apr 10, 2013 | Discussions thread
qianp2k
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Re: Return of Interesting article on DxO about 5D III and D800...
In reply to Steen Bay, Apr 13, 2013

Steen Bay wrote:

qianp2k wrote:

KLO82 wrote:

Steen Bay wrote:

qianp2k wrote:

Steen Bay wrote:

aftab wrote:

Now, let us look at scenario B and scenario C again. In both cases A looks sharper than B. What does that mean? More resolution = more sharpness. That is resolution = sharpness in this two scenarios. And almost all scenarios are like this. So, we can actually use the terms resolution and sharpness interchangeably.

But if comparing for example the 12.7mp 5D vs. the 18mp 7D, then things get a bit more complicated, because it seems that 5D (most often, with most lenses) has the best sharpness (MTF-50?),

true.

while the 7D has the highest resolution (MTF-10 or MTF-5?).

Not necessarily. Actually with most  EF lenses 5D outresolves 7D if you frame them in the same AOV (as tested by DXOMark in either old MTF or new P-MPix unit that are two different expressing units but with the same result). Only very few lenses such as with 300L/2.8 IS II 7D/60D outresolves 5D.

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But what if we could compare the MTF-10 er MTF-5 values (which we unfortunately can't anymore)? Then I think that the 7D would win, because it has quite a bit more MPs.

This is what you are talking about:

In the 2nd pic, I was supposed to highlight the MTF 20, but instead wrongly circled the MTF 30. Dxo used MTF 20 as resolution ("critical" resoltion or something like that. I cant remember the exact term).

Thanks for saving the snapshots of old DXOMark test in MTF unit before DXO changed to P-MPix unit.  Regardless of what unit DXOMark used, it shows the same clear result.  So P-MPix should not be an excuse for those deny/challenge DXOMark tests as from what I have seen and remembered the test comparison results are consistent with former MTF and the latter P-MPix.

Yes, thanks to KLO82 for that.

With one of the best lenses 100L, we can see both systems are very close but 5D still edges out a little bit.

With a bit lesser lens 85/1.8 (still very good lens), 5D leads wider.  With further inferior lenses, then 5D will further widen the lead.  The result is clear as we have seen from tons of real world photos from respective cameras.

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We can also see that the 7D actually has a higher resolution. The 5D's MTF curve stops at app. 61 lp/mm because it runs out of vertical pixels (app. 61 lp/mm represents the 5D's Nyquist frequency), while the 7D's MTF curve continues to app. 72 lp/mm (on 24 x36mm). The contrast is rather low, but the 7D's resolution is nevertheless higher.

I'd suggest everyone reads these articles to understand these concepts first and understand what that means in real world photos.

http://www.normankoren.com/Tutorials/MTF.html

http://www.imatest.com/docs/sharpness/

From above two DXOMark MTF tests, we can see 7D only extends at MTF 15% or below that virtually invisible by eyes in real world photos even at base ISO when 7D photos buried by higher noises/grains. So that 7D higher resolution (18mp vs 12.8mp from 5D) is only on paper or reflected in larger CR2 file size but unless you have an eagle eye, you just cannot see it

More meaningful MTF 50% or at least MTF 30% are truly what your eyes will enjoy   That's main reason why DXOMark changes to "perceptual sharpness" measurement as most people truly confused by MTF data, which MTF data?

I have some quotes from above two links,

Contrast levels from 100% to 2% are illustrated on the right for a variable frequency sine pattern. Contrast is moderately attenuated for MTF = 50% and severely attenuated for MTF = 10%. The 2% pattern is visible only because viewing conditions are favorable: it is surrounded by neutral gray, it is noiseless (grainless), and the display contrast for CRTs and most LCD displays is relatively high. It could easily become invisible under less favorable conditions.

The eye is relatively insensitive to detail at spatial frequencies where MTF is low: 10% or less

This measurement, also called “vanishing resolution”, corresponds to an MTF of roughly 10-20%. Because this is the spatial frequency where image information disappears— where it isn’t visible, and because it is strongly dependent on observer bias, it’s a poor indicator of image sharpness.

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