Wow, thanks, AG. One thing I did notice was the steep gradient of some
developers on the 100TMX CI curve (D76) as opposed to the smaller
gradient of TMAX. I guess that gives TMAX users some reprieve in terms
of time and temperature variations.
I developed 100TMX in TMAX for 6.5 minutes at 20 degrees celsius. Since
my negs were not overexposed, it looks like I can enjoy all the shadow
detail with all other tones evenly seperated. I'll let you know how they
print!
AG Schnozz wrote:
>>Ok, I understand the MTF curves and the spectral sensitivity
>>curves, but
>>what exactly am I looking at on the characteristic curves and
>>contrast
>>index curves for 100TMX? I can see for instance from the CI
>>curve that
>>if I process the film longer, the CI goes up, but how is the
>>CI defined?
>
>
> I personally don't spend too much time worrying about CI curves
> as my developer of choice (DD-X) works a bit differently.
> However, the explanation is this: A CI curve is essentially
> indicating a ratio of some form of the maximum density of the
> negative. Look at the following link:
>
> http://www.kodak.com/global/en/professional/support/techPubs/f4016/f009_0450ac.gif
>
> You can see from this that development time of most developers
> will adjust the contrast of the negative. The more you develop
> it, the greater the contrast. TMX100 in HC100B for 6 minutes
> will produce a soft negative that is good for preserving
> highlights. (expose for lows, develop for highs). Processing the
> same combination for 14 minutes will increase the contrast to
> the maximum possible with the emulsion.
>
> This is only part of the story, though. This gives you the
> development times to handle maximum and minumum contrast ratios
> with that particular film/developer combination. But it does
> not indicate anything about the shape of the response curves.
>
> http://www.kodak.com/global/en/professional/support/techPubs/f4016/f009_0439ac.gif
>
> The above graph shows that TMX100/Tmax Developer does have a few
> nuances that bug many people. With the 12-minute curve, you see
> a Zone IV bump but a Zone VI dip followed by an out-of-control
> lifting of the highlights that will cause blocking. 7-minute
> developement brings most of these peaks and dips into alignment
> and creates a smooth straight-line section that goes right up to
> the maximum density at that development time. TMX has no
> "shoulder" to speak of. As such, TMX is a film you do not want
> to over-expose. You must nail the exposures.
>
> Now let's look at Tri-X:
>
> http://www.kodak.com/global/en/professional/support/techPubs/f4017/f009_0492ac.gif
>
> What you see here is a long straight-line section, a gently
> curving toe (preserving Zone I-II details)and a slight shoulder
> that preserves highlight details.
>
> One more to compare. Let's look at Plus-X in D-76:
>
> http://www.kodak.com/global/en/professional/support/techPubs/f4018/f009_0433ac.gif
>
> The toe is similar to Tri-X, the straight-line section is even
> from Zone II-VII which gives near-perfect tonal seperations and
> a gradient to die for. Look at the shoulder. See how it
> flattens out? You will find details in the highlights and it's
> a bit more forgiving to over-exposure. You can see why this
> film/developer combination is so loved. Other than grain
> structure, this is among the very best film curves ever.
>
> One last one to look at. Ilford XP2:
>
> http://www.ilford.com/html/us_english/pdf/XP2SGB_QX.pdf
>
> On page two of the PDF you see the characteristic curve. First
> of all, note that the density of the negative is very low.
> Secondly, see that the response curve goes right from the toe to
> the shoulder. The greater the exposure (more light), the more it
> gets compressed. There is no straight-line section so you do
> lack tonal seperation and an even gradient from high to low.
> Even though highlight details are preserved, there is so little
> tonal seperation from Zones VII-X that the highlights lack snap.
>
> I'm not dissing XP2, here, just pointing out how it compares to
> traditional films. When scanned (it scans very well), you will
> usually need to lift the highlights to counter this compression.
> In the darkroom, it favors papers that have opposing response
> characteristics. (Forte).
>
> So, back to the original question. CI essentially refers to the
> maximum density on the negative of the recorded highlights. The
> denser the negative, the less contrast is required for the
> paper. There are two schools of thought--high contrast neg/low
> contrast paper or low contrast neg/high contrast paper.
> Personally, I like middle of the road ones that give me some
> flexibility either side during printing and stand up well to
> split-grade printing and paper-flashing. If you scan the negs,
> you will want to lean towards softer negs. High-density negs do
> not scan well and you'll lose highlight details. As always
> YMMV. It's best to pick a middle-ground than to hit the
> extremes.
>
> AG
--
Matt Boland (BEng) Phone : 61 7 5594 9824
R&D Engineer Mobile : 61 4 0835 1421
Odyx Corporation Pty Ltd email : mattb@xxxxxxxxxxx
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