All the qualities of a lens can be expressed in mathematical
terms. When these figures are favorable I am usually persuaded
that the lens is good. I rely entirely upon the contrast
transfer function measured in a good laboratory for that warm
confident feeling I get when I fit the Sigma Apo Macro Super
70-300mm (35mm) or the Sigma Macro 50mm (35mm) lens to the *ist
D. Why? Because I no longer use film and know the images are as
good as one can possibly get with that particular digital camera.
However, using an ordinary, slightly modified, web camera on a
microscope that sits on the table behind me, I am able to
resolve to the absolute limit of visible light and can image
objects less than 200nm apart. By the way I have many hundreds
of the same kind of images made with the *ist D and also on a
range of different kinds of film. None are any better than the
640 x 480 images made with the web camera. UV light (dangerous)
improves resolution considerably.
Using digital it is also possible to stack many (hundreds) of
images and use a range of sophisticated software to produce more
visually satisfying pictures.
Happy New Year everyone.
D
Dr E D F Williams
41660 TOIVAKKA
Finland
Ph: +358(0)400706616
On 31/12/2010 23:25, Steven Desjardins wrote:
Well, Wikipedia has nice summary for this:
In photography, acutance is the edge contrast of an image. Acutance is
related to the amplitude of the derivative of brightness with respect
to space. Due to the nature of the human visual system, an image with
higher acutance appears sharper even though an increase in acutance
does not increase real resolution
On Fri, Dec 31, 2010 at 4:20 PM, Mark Roberts<m...@robertstech.com> wrote:
Steven Desjardins wrote:
On Fri, Dec 31, 2010 at 2:31 PM, mike wilson<m.9.wil...@ntlworld.com> wrote:
On 31/12/2010, Godfrey DiGiorgi<gdigio...@gmail.com> wrote:
edge definition
As good a definition [8-)]as you need for most things.
IIRC, it can be casually thought of as how (fast) an edge goes from dark
to light, hence the connection to edge definition.
That's it.
Acutance is the rate of change between the two sides that form an
edge. Resolution is the number of edges you can put in a given space.
Sharpness is a combination of both characteristics.
http://www.luminous-landscape.com/tutorials/understanding-series/lens-contrast.shtml
http://www.luminous-landscape.com/tutorials/sharpness.shtml
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