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[OM] Re: BW Paper revisited part II

Subject: [OM] Re: BW Paper revisited part II
From: Matt Boland <mattb@xxxxxxxxxxx>
Date: Sun, 17 Oct 2004 09:46:21 +1000
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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