At 11:24 21/09/2000 +1000, you wrote:
>Murphy, Bob H <[EMAIL PROTECTED]> wrote:
> > Why won't a piece of white paper under exposed by 2-1/3rd stops produce
>the
> > same exposure as an 18% gray card?
>
>Because a grey card photographed with a 28mm lens at 2 metres won't be full
>frame? The main thing I'm concerned about is differences in grain due to
>underexposure. Perhaps some of the more experienced photographers
>on the list could comment, but I would feel more confident comparing grain
>effects in "correctly" exposed negs/slides than in film exposed outside its
>latitude.
>
>Rob
All modern films have a multilayer construction, each R, G, B - sensitive
layer consists of 2 or 3 layers of different speed (grain size). The bigger
the grain, the bigger the speed. If you underexpose a film, you record an
image in more sensitive layer, which is grainier. That construction allows
for a bigger exposure latitude.
why do you need 28 mm lens at 2 m distance to measure/assess the grain? the
image doesn't have to be sharp to determine grain size. According to a
standard, the grain is measured on an uniform gray (D=1.0) using an
aperture of 48 microns. According to Fuji-
diffuse rms granularity of Velvia RVP is 9, Provia RDPII 10, Sensia II (RA)
10, Astia RAP 10, Fujichrome MS at EI 100 10, EI 200 11, EI 400 13, EI 800
15, EI 1000 16, Provia 400 RPH and Sensia RH 15, Sensia 200 RM 15,
Fujichrom prof 64T 11, Fujicolor NPS 160, NPL 160, NPH, Superia Reala CS ,
Superia CN, Superia 200 CA, Superia 400 CH - all have rms granularity of 4
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