Identify Sharpness & Quality


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tSkye

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Nov 8, 2005
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Farrer Park
#1
This maybe a technical discussion, I hope you can bear with me.

A lot of photographers and testers use Lp/mm to identify the camera's resolution.

As quoted:
"Line pairs per millimeter (Lp/mm) are the optics industry's standard measurement for defining the resolving potential of camera lenses, film, digital sensors."


I also refer to the MTF charts which indicates the lenses' performance.

Link:
http://www.luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml


Some also associate this with sharpness, by saying that the number of line pairs per millimeter that can be distinctly resolved is what defines the resolution of the camera, and thus, applying it to an image, if I can distinctly tell apart the lines, it means it's sharp up to that certain extent.

The questions:
1) What is the definition of distinct?
2) Is there a quantifiable number that is able to identify between distinct and non-distinct?

Example:

The image on the left is taken at f1.8, the one on the right is taken at f8.

One can tell that the one on the right seems to be sharper.
But is there a way to quantize them into numbers for comparison?
 

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tSkye

New Member
Nov 8, 2005
989
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Farrer Park
#4
Oh, yes. So basically if I could make out the lines of a certain graph, ie 2.8, then I multiply it by the magnification factor, I am able to use the Lp/mm to determine the sharpness.

However, in the real world scenario, am I able to pick a picture and determine the sharpness from different sections of the image? Like focus on the face and see the fineness of the hair on the eyebrows? Or like check the blur of the background, then determine the Lp/mm or sharpness parameters?
 

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