Is DXO Right - D800 only 2-3 mp more than D600

Started Mar 17, 2013 | Discussions thread
FrithjofA
Contributing MemberPosts: 905
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Re: Question of definition
In reply to A Owens, Mar 19, 2013

A Owens wrote:

If we take the Nikons best lens (85/F1.4), DXO reckons that the D800 will only give 3 more MP than the D3x, possibly only 2 MP gap than the D600

The Dxo  P-Mpix score is a very good example for a misleading quantity.  All information is already contained in the MTF chart, the lens manufacturer provides you.  DxO came up with the definition

(http://www.dxomark.com/index.php/Publications/DxOMark-Reviews/Looking-for-new-photo-gear-DxOMark-s-Perceptual-Megapixel-can-help-you)

"Perceptual MPix: a much simpler tool to score and compare lenses

P-Mpix is the unit of a sharpness measurement. The number of P-Mpix of a camera/lens combination is equal to the pixel count of a sensor that would give the same sharpness if tested with a perfect theoretical optics, as the camera/lens combination under test."

The key sentence part is  "..would give the same sharpness if tested with a perfect theoretical optics,..."  we all know, that a "perfect theoretical optics" does not exists. Therefore, the conclusion, that P-Mpix score is equivalent to real life MP is a misconception people gain from a quantity called "Mpix".

"sharpness measurement" is already misleading, since a sharpness is a subject impression. Probably "resolution" is meant which is measure via contrast. We all know, that you can resharpen photos but you cannot increase the resolution of your Lens/camera combination, since it is a hardware property.

Resolution is given by a single point of the MTF curve. However, you can read out much more information from the MTF chart than sicj a single number!

Therefore, DXo provides no new information about a lens. Such a score has two function:

(i) create interest in a company such as DXO to help marked their produces

(ii) provide misleading lens quality data by condensing everything into a number which you can compare, suggesting the bigger the better!

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