----- Original Message -----
From: "Joe Gwinn" <joegwinn@xxxxxxxxx>
<snip>
> When comparing various cameras and scanners, we probably should always
ascertain the optical resolution of the green channel alone, and use that as
our comparison. These numbers will be directly comparable to the
resolutions of black&white film and cameras.
>
Well, thanks for the details analysis. I think it is not so proper to count
just the green channel, assume you use the CCD for B/W photo, every pixel
will be used for resolution information. For color it will also be close,
but some details' color could be wrong, making a not so "clean" picture but
the "resolution" should be there.
It is very difficult to make a "true" resolution assessment here. Just like
the resolution of film camera system, as I mentioned before, a CCD pixel
will contain 256 different levels (assume 8 bits) but the film color
(information) is composed by grain, a few dots may be good enough to compose
a line to represent resolution data but this few dots will not be as
informative as a CCD pixel. This favor to film, in resolution test film will
be the winner.
Since each CCD pixel is so informative and clean (compared to the dot grain
of film), that is why in many case a 4-6MP DC showing picture quality better
than film. Ok, the details may not be as good as film but overall it look
better.
>
> Actually, this leads to a good question for CH: Has he or can he measure
the resolution of his scanners? If one can find a suitable resolution chart
and scan it, it ought to be easy. The scanner maker probably also knows,
but may not be willing to publish the modulation transfer function.
>
I don't have a professional slide for scanner test, but I do have a lens
test slide, below is a crop of Zuiko 50/3.5 at F5.6 shot, exposed with flash
so vibration should be minimized. The size is 5.2mm x 2.1mm, download it in
PhotoShop to check the resolution, to me it looks over 75lp/mm.
http://www.accura.com.hk/50-02.jpg (200K)
Below is a message I posted before to compare a simulated 16MP DC and 35mm
film system, enjoy!
==============
May be we start another interesting topic about how many pixel a DC can be
comparable to a common film we are using.
I just perform a test with E-10, shooting at 140mm (35mm equ.) and Fuji
Provia F shooting with 35-105 at 70mm. E-10 is a 4MP DC, I try to simulate a
16MP DC by setting it to 140mm and compare it to a shot taking at 70mm. The
file is a bit large (around 1.1MB and 1.7MB each). But it is interesting to
have a look.
The 70mm shot taking with Zuiko 35-105mm (early version) at 70mm F8, tripod
and shutter speed was 1/250. Scanned at 4000dpi and cropped the center
179.mmx13.4mm. I have made three shoots, two with 35-70/3.6 and one with
35-105, they all have similar resolution but the 35-105 has slight higher
contrast.
http://www.accura.com.hk/70mm.jpg
This is a E-10 shot at 140mm, ISO80, F4.8, 1/640s, sharpness setting: low
(F4 is the best aperture of E10)
http://www.accura.com.hk/E10-140mm.jpg
I don't make any comment, download them and check it out yourself by making
side to side comparison, you may need to see the different in 200% view.
C.H.Ling
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