From: donl@glass.esd.sgi.com (donl mathis)
Subject: Re: Large format color negative questions
Reply-To: donl@glass.esd.sgi.com (donl mathis)
Organization: Silicon Graphics, Inc., Mountain View, CA, USA
Distribution: usa
Date: Thu, 30 Jul 1992 17:48:49 GMT


In article <0beZ032c4aEN00@amdahl.uts.amdahl.com>, bjs@uts.amdahl.com
(Barry Sherman) writes:
|> I've been printing Cibachrome off and on for a couple of years total
and have
|> been doing so at home for a few months now.

My condolences.  :)

|>   Do *you* use VHS?  VHC?  Something else?  Because of my background
|>   doing Cibachromes I'm more than a little leary of any color film that 
|>   promises *more* contrast.  I really hate it when the shadows drop off the
|>   scale and turn into black holes.

A distaste for black holes is a good reason to switch to negatives from
transparencies.  (A distaste for artificial flavors and colors is
another, but I won't mention that here.  Not now.  No sir.)

I've used both, but never in a side-by-side comparison.  In general
use, and in the plotted curves, I've never really noticed a strong
difference in the contrast.  Remember that (Kodak) RA-4 papers come in
three contrast grades, which offers a bit of flexibility that you don't
usually have with color materials.  I suspect that there's more of a
difference between the grades of paper than between these two films,
but I can't quantify it.

You'll want to look at the grain of both films with respect to big
prints.  I can't remember if VHC is a newer (i.e. T-grain) film or not;
VPS definitely is the "old" kind, and can look a bit rough under high
magnification.  I can't make prints over 5x (which is 20x24) so VPS
grain doesn't bother me.

I primarily use VPS; I occasionally have some VHC floating around, but
I don't go out of my way for it.

|> * I notice that what little literature I can find recommends what I 
|>   consider to be rather abbreviated exposures as the longest that are 
|>   recommended for use with these films.  Somewhere in the 1/10 second
range or 
|>   so, if my memory is functioning reasonably well.  This worries me since I 
|>   rarely get to use an exposure that short with my view camera. 
Times of 1/4" 
|>   or longer seem to be more the norm. Has anyone had any experience
with the 
|>   reciprocity characteristics of these materials?  Color shifts as well as 
|>   exposure non-linearity?

I've never measured the reciprocity characteristics, but I have also
never worried about them, either.  I just do my normal view-camera
thing, with normal view-camera exposure times (often *much* longer than
1/4 second).  I can't think of any occasions where reciprocity failure
has caused a problem.

|>   Naturally I put this off until the last minute and it's too late to have
|>   Kodak send me data sheets on these films.  I was surprised that there were
|>   no data sheets in the boxes.

I'm surprised, too -- I've never bought a box of Kodak film that didn't
have a data sheet inside, in at least 47 languages.

|> * I notice that the film VPL is designed for long exposures under tungsten
|>   light.  Naturally, that makes me wonder about avoiding reciprocity
problems
|>   by using this film along with the appropriate filtration.  But I have 
|>   this hunch that its speed might be prohibitively slow or that there
|>   might be some other problem.  Any thoughts?

Probably not worth the trouble.  It is slow to begin with, and you'll
lose a lot more light with the requisite blue filter.  My suggestion is
to not try and solve the long-exposure problem with daylight film until
you actually *have* the problem.

|> * I often hear it recommended that VHS be exposed at 120 or so rather than
|>   160.  Opinions?  Also, I believe that VHC is rated by Kodak at 100.  (I
|>   can't believe that they don't print the speed on the boxes of this 
|>   stuff.)

They don't print the speed on the side of the box because they red-stamp
it on the data sheet you didn't get inside the box.  They reserve the
right to change it, according to the emulsion batch, but that never
happens -- it's always 160 for VPS.

|>   Any suggestions on an EI to use for VHC?  Once again, I don't think 
|>   that I have time to test for my own EIs before leaving.  My natural
|>   inclination would be to use an EI of 64 or 80 for the VHC, based on
Kodak's
|>   rating it at 100.

One thing to remember about these films (although I'm more sure of VPS
than VHC) is that they have a very long, very straight curve.  I once
measured VPS at 12 stops, and ran out of data before the curve flattened
out.  VHC is probably similar.  That means you don't have to worry too
terribly much about overexposing.  I shoot VPS at 100.  It's "real"
speed (by some vague definition I'm not prepared to give) is probably
about 120, and shooting it at 100 gives a good solid thump to the shadows.

|>   However, in case I do, does anyone have a recommendation on technique?  In
|>   doing b/w tests I usually just do a bunch of gray card exposures from -5 
|>   stops to +5 stops in 1/2 stop increments, find that which produced a 
|>   density of .1 over b+f and calculate the EI based on that being a Zone I 
|>   exposure.  But with color negatives I have no idea of what density 
|>   to look for or how many stops below meter reading should produce
|>   that density.  I guess that what I'm really asking for is a rough 
|>   correlation between f-stops and Zones for color negative materials.  

You can rate the speed more or less the same way you rate the black and
white stuff -- use 0.10 over film base plus fog, or just look for the
frame that start to give workable density and texture, so you know you're
up off the toe.  It's all straight uphill from there.

There are two problems, here -- one is the film speed and scale, and the
other is the paper's range.  What typically happens is that you can put
10 or 12 stops of subject range on the film, and then you can pick your
favorite 7.5 of them to put on the paper.  Actually, with the softer
VPS and softer paper grade, you can get more than that on the paper.
The definitions of highlights and shadows are a bit more subjective than
in black and white work, so you'll have to decide for yourself where the
limits are, and what the corresponding film densities and hence subject
ranges are.

You have a distinct advantage in testing color materials -- your film
development and contrast has already been decided for you!  All that
remains is to expose a scale on the film, and see how it prints on the
various papers.

|> * So when are they going to make 4x5 Ektar 100? (Not to echo donl.
:-)  Based 
|>   on my 35mm experiences, I think that Ektar 25 is a little short on
exposure 
|>   scale for my tastes for general use and the speed seems a little low for 
|>   general view camera use.  But the 100 seems like it would be a real
winner.

I agree.  They probably never will.  You and I do not a market make, in
Kodak's eyes.  I asked them about it once, even special order and that
sort of thing, and they said there's more to it than that.  They
basically have to build a coating-and-cutting machine for each product,
and it costs millions of dollars.  They don't make big sheets of film
and cut them up later; it all happens at once.  Based on market demand
for sheet films (small), and color negatives (smaller), and those of us
who want a film with Ektar's characteristics (smaller still), we're
unlikely to get what we want.

My partial solution was a roll-film back, with which I can make 6x7
negatives on Ektar, Reala, or whatever other 120 or 220 film strikes my
fancy.  The film is good enough to survive the additional enlargement,
which is something like a factor of 2 more than for proper film.

- donl mathis at Silicon Graphics Computer Systems, Mountain View, CA
donl@sgi.com
Newsgroups: rec.photo