Defocusing and grain

[Arthur Entlich <artistic-1@xxxxxxx>]

I finally got the opportunity to see what happens by defocusing my 
Minolta Dual II as a way to reduce dust dirt and grain.

The first thing I did was to see who much difference there was between 
an autofocused slide and one which I manually focus.  As I somewhat 
expected, the manual focusing created a sharper image, by a bit, perhaps 
a 5% difference.  Based upon the fact that as it is the scanner 
emphasizes DDSG, the last thing to do is "improve" focus any more than 
necessary.

It took several attempts at defocusing using the manual focusing process 
to figure out how much defocusing occurred based upon the graphic slider 
control.  I finally came up with a difference of about 1/4" difference 
between the peak focus (contrast) white bar, optimized for highest 
contrast, and the black bar, which indicates the current contrast/focal 
position.

This creates a noticeably soft result.  The "good" part about it is it 
reduced grain and dirt/dust considerably.  The bad part is that although 
  I had many less of the typical speckled  type of sharpening artifacts, 
when I used USM, the amount of USM necessary to make the image look 
sharp created a different artifact - overly accentuated edge definition.

There is probably a middle ground, which would decrease the DDSG while 
not requiring the need for such high amounts of USM, and when I have the 
time, I will further experiment to try to find that best point.

Unfortunately, however, using defocusing alone cannot resolve the 
problems with the Minolta scanners, although careful use might diminish 
some aliasing and other grittiness. Now the question I have is, what 
exactly is up with Minolta scanners that causes them to so exacerbate 
DDSG when using what should be a lighting source that diminishes those 
aspects under most circumstances.

Art


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