One more thing (I'm agnostic about film and digital, both having strong and
weak points), I've seen a transparency that had no grain (way above 3200dpi)
and a digital image that exceeded the nyquist frequency[1] limit by a factor of 2.
These are extremely rare occurrences but do exist. Almost all claims to be able
to achieve these results on a regular basis should be dismissed out of hand (sigh).
That aside, we need to be aware of is the weakness of dslr's and digital backs
since we are using these for calibration tools and are a part of our (or at least
my) daily work flow.
Because of the well known RGBG arrangement slight differences in colors are
the Achilles Heal of the 40Mega-pixel chip.
The full color pixel value is 40mp/RGBG (four photo sites) == 10 megapixel color camera
I've been using and selling Charles Sleicher targets (RGB and Black on White)
for awhile. To see the 10 mega pixel effect make red line pair targets
on a red background with a sinusoidally decreasingly small difference in color.
At some point the scanned film image will show up to 2-3 times the resolution
(lp/mm) as compared to the dslr or digital back image (given 2G photosites and
perfect point algorithm mentioned in Note 1 on the bottom of a highly intelligent
and no doubt expensive, stack of software).
This is only being pointed out to show that the digital image will lose some
of its color acutance as it approaches the megapixel/RGBG limit.
Given what I've seen (both good and bad) from film and digital sensors I
would be comfortable estimating that a well exposed color balanced piece of
6x6 or greater mirror like flat piece on film (using the fine focusing loupe lp/mm
kit I sell) behind a good Schneider, Nikon, Zeiss etc. APO lens will out capture
the finest color detail of the large format 40 Mega pixel back (based on a
2800dpi 16bit nikon fluid scanning limit for color film).
I did not account for the less than 16bit per channel color depth of the kodak
KAF-39000-AAA chip (has anj internal 12bit dynamic range but outputs 16) so
just think of that as my four bit margin of safety.
A lot of 4x5 film verses digit test reviews have been popping up which I'm having
trouble with.
My Engineering Test Requirements
The first is I want to see a picture of the reflection of an unexposed
piece of film in the film holder to check for flatness. The reflected image
should be perfectly mirror like, demonstrating no out of the box film curl.
(As far as I know flatness can only be obtained by a specific unexposed
film taping technique in the black bag or dark room).
The second is I want to know is the reviewer used my fine focusing loupe kit (for
precision plenum photography) that will bring the lens image and emulsion plane
into perfect focus simultaneously (across the entire frame inspected on the
side and corner stand). Once observed (validates most of the camera system
and) it guarantees the best possible image resides within the approximately
.001 to .002" emulsion plane.
The reviewers will only need to pay actual postage to them AND back to me
(unless they want to buy it or craft their own from almost 70 pages of
documentation, photographs and drawings that comes with every kit).
I don't like to name names but some of great renown have done that and more
for me, so its time to give back to those who share one of my life's great
passions.
Note [1]
40Mega-pixel the monochromatic value. There also is a airy-disc (perfect-point)
algorithm being used that can make digital pictures "scary". But I digress, I do not
even know if its published (a tightly held trade secret no doubt). Simply put it is
possible (with high speed sampling deterministic algorithms) to achieve reliable sub
pixel accuracy (yes, exceeding the monochromatic 2d nyquist frequency limit in
something resembling a virtual 3d working space).
There was also a very fine diffusion filter used in an attempt to emulate the
Super-Angulon 8/65mm (magic glass)
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