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:

Steen Bay wrote:/

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

A bit of sharpening makes it easier to see. It's clearly visible if comparing the resolution test chart shots in DPR's 5D and 7D reviews.

a) that depends from shooting distance.  A meaningful test should be done from at least 50x focus-length distance; b) depends on which lens. 7D needs a really good prime such as 100L (85/1.8 is also very nice lens) under perfect neutral gray and grainless/noiseless light condition at base ISO 100; c) doesn't reflect in real-world photos in outdoor harsh light or indoor poor light; d) depends on measured in center-only, or also in edges/corners so on average resolution.  5D is especially better in edges/corners even with the best lenses.

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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