Slide film has a non-linear density curve vs. exposure, as compared to print
film (which has other density curve issues regarding scanning, but is fairly
linear).
Slide film's greatest slope in the exposure/density curve occurs in the
middle of it's exposure latitude. This results in densities in that range
of exposure having slightly exaggerated differences (more noticeable
gradations are recorded in that range of exposure). The tails of the curve
(dark and light portions of image) behave in the opposite manner,
compressing similar ranges of exposure intensity into a much smaller range
of densities (thereby losing the ability to discern slight changes in
light).
That is one reason why slides are less forgiving than print film with regard
to exposure errors. Velvia's curve (http://www.fujifilm.com/AF3-960E.pdf)
is steep in the middle. As such, underexposing high-key images causes the
important bright regions to be brought down to the middle region of the
exposure curve, increasing the ability to distinguish minor differences in
the lightest parts of the image. Likewise, overexposing low key images
brings the darker regions of the image up into this steep part of the
exposure curve, allowing finer differentiation of the darker parts of the
images (and lightening them). The tradeoff of this method is that with
low-key images, the highlights become completely washed out, and with
high-key images, the shadow detail turns black and disappears altogether.
But the main point of interest becomes the most discernable (dark or light
portions, respectfully).
Fuji's recommendations are actually good recommendations for all slide film,
since they all share the same characteristic exposure/density curves, though
Velvia's may be more pronounced.
Does this make sense?
Cheers,
Gerald
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, May 09, 2001 8:26 AM
Subject: Re: Velvia questions
> Robert Harris wrote:
> Fuji knows that majority of professional photographers set their cameras
> at E.I. 40 when they shoot Velvia. We think this is very reasonable. At
> the same time, Fuji recommends that photographers try E.I. 64 when you
> shoot high key images where whites are very important. Also, we
> recommend trying E.I. 32 or lower when shooting low key images with
> Velvia.
>
>
> I don't understand. Adding light in low key (overexposing), and
substracting in
> high key (underexposing)?
>
> Please somebody explain! Thanks
>
> Albano, a bit confused
>
>
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