At 05:04 PM 5/10/2005, Moose wrote:
>More to come, I think, as I haven't answered all my own questions yet. I
>just started looking at some Royal Gold 400 I shot on the same trip and
>the grain in the scans is less than the Vista 200. This either means that
>Vista is pretty grainy or that some aliasing thing is going on. The grain
>in the RG 400 is about what I remember from scanning it in the
>past with a 2720 dpi scanner.
>
>Moose
Moose,
I don't know about the Vista 200 . . . however Kodak's premium Royal Gold
consumer films were much finer grained than the Gold. Some of them were
pro films shipped green(er) and unrefrigerated (Royal Gold 25 and Ektar 25
were the same film).
Unfortunately, Kodak uses a completely wacko "Print Grain Index" for its
color negative films . . . pro and consumer . . . that cannot be compared
to anything else. As a comparator of Gold versus Royal Gold though (some
indication of how Royal Gold stacked up against non-premium films):
Royal Gold 25: < 25 (lowest value on Kodak's PGI scale = 25)
Gold 100: 45; Royal Gold 100: 28
Gold 200: 47; Royal Gold 200: 32 (now called High Definition 200)
Gold 400: 48; Royal Gold 400: 39 (now called High Definition 400)
Max Zoom 800: 48; Royal Gold 1000: 57
That was the really, way cool thing about Royal Gold . . . its ISO 400 beat
out Gold 100 in resolving power. Royal Gold 1000 . . . at 1/3rd stop
faster than Max Zoom 800 . . . is the only one that was a disappointment in
terms of resolution. Kodak's Supra 100 and 400 were nearly the same as
Royal Gold, and it's 800 was nearly the same as Max Zoom.
BTW, the diffuse RMS granularity between negative and transparency films
cannot be directly compared. An approximate heuristic for comparison is
multiplying the color negative RMS numbers by 2.5 ("Photographic,"
1996). RMS is a non-linear scale; a difference of "1" on the scale is
twice the graininess (e.g. 10 is twice as grainy as 9).
I found the following *approximate* conversion for Kodak's wacko PGI to RMS
granularity on Photo.net and don't know how accurate it is (or isn't) but
it at least appears to be somewhere in the ballpark:
RMS = (PGI / 0.5335) ^ (1 / 2.8669)
The troubling aspect of this equation is the non-linearity of the RMS scale.
The inverse of this to get an estimated PGI from RMS:
PGI = 0.5335 * (RMS^2.8669) [Remember to approximate color neg RMS by
dividing a chrome RMS by 2.5 first).
As a sanity check, Kodachrome 64 has a PGI of 28 using this equation.
Using this with Agfa Vista 200's RMS of 4.1 gives a PGI of 30 which is less
than Royal Gold's 400's PGI of 39 and this doesn't pass the "sanity" test
of Moose's observations . . . nor does it (IMHO) fail it either (possible
ambiguities about reason; could be something else at play here). Fuji
Reala has a PGI of 28 (RMS = 4).
Source of the equations is Michael K. Davis and was found in some USENET
postings, and on Photo.net in their forum. He generated the equations from
three known pairs of measured PGI and RMS data . . . which may not be
enough sampling.
-- John Lind
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