"curves" in chemistry

[menashe_soffer]

Hello

 

I am experimenting with negative to positive (slides from negatives).

Using TMAX-100 to create the positives and home-made D-19.

 

The problem is that the darker araes sems to be condensed.

I did not make accurate experiments but I can say that according to impression I get from real images. I can

quantitavely explain my expression in zone terms.

 

agree that "Zone 10" is black on original negative / white on positive.

Than my impression is that zone 5 becomes 3 (darker than it should be) so there is too much definition in the

ligher zones a.k.a zones 6-10 streching to occupy 4-10 on the expanse of the darks zones 1-5 contracted to 1-3.

 

Which variables I can use to controll the "shape" of the curve and how (change ingrediants fraction in the D-19

formula, push/pull, agitation, dilution).

 

thanks

[evan_goulet]

D-19 is a high contrast developer. My only experience with it has been in the development of electron microscopy negatives on scientific film (4489 I believe). These were transmission electron microscope images which tend to need high contrast. So it may just be the wrong developer for what you want to do.

[lex_jenkins]

Haven't tried this myself in so many years I can't remember anything, but...

 

Check the dr5.com website. They specialize in this and may have some tips on the website. Also, I seem to recall seeing some PDFs on the Ilford site with tips for processing positive transparencies.

[john_hugens]

I find that less developer over more time equals a longer curve, less agitation helps.

 

However, I can't find much in developing that'll pull your shadows up. I've always learned it as expose for the shadows, print for the highlights. If you look on the zone system website, http://photography.cicada.com/zs you'll find a few graphs linked to density curves. However, I don't think you can do much for a zone 5 or below as those areas are dictated more by your exposure than your developing time. Also, have you looked at changing your paper? I've found that in order to get a deep black a lot of papers have a high compression of blacks - paper that ascends in a linear manner is just not that interesting to look at :-). So, try developing longer with a thinner soup and printing at a 00 contrast filter. If that doesn't boost your dark areas up I don't know what else to tell you beyond try a developer with a different curve. I might be wrong here, I've got a nasty habit of mixing all the right stuff up in the wrong order. So if that fails, try the reverse and it'll probably work just fine.

 

best,

 

-John

[jordan_w.]

I'm not sure that anyone read Menashe's question!

 

If I understand correctly, he is trying to make positives by re-photographing negatives onto TMAX 100 film (using a slide duplicator or macro lens) and then developing the TMAX in D-19 to get positives. This is similar to the process described here: http://www.dealfaro.com/home/bwslides.html There's no reversal processing (DR5 won't help) and no printing going on.

 

I've used this technique, although with Eastman 5302 film (an electron-microscopy film). It works well and the positives look good. The key is to experiment with exposure. I'm sure that TMAX will react differently and you may not get the look you want. If you can get your hands on some slow, high-contrast film (like lith film?) that may work better.

[patrick_gainer]

Films are designed to have a very long exposure range between 0 and Dmax. Even though Dmax is quite a large number, using ordinary film as a printing medium requires a heck of a lot of exposure to make a true black which then requires miniscule development to maintain clear whites. In the days when we still called the slope of the characteristic curve "gamma", we talked about "gamma product" which is the product of the gammas of positive and negative media. This product should be nearly 1 whether we are making reflective prints or transparencies. There is always some room for artistic license, but if we get too far away, we have soot and chalk or dullness.

 

When you make a direct transparency, you use the silver that's left from the negative to make the positive, so you can (usually) do it in one film. If you develop a film to gamma = 0.5 for the negative, you must find a film and developer that can bring up gamma = 2 or even more. Now if the negative is developed to gamma = 1, the same film can usually be used for the positive provided fog is not too great.

 

Sorry for the lecture. Jordan knows more about it.

[jordan_w.]

Menashe, have you tried using a paper developer like Dektol?

[menashe_soffer]

thanks for the answers;

 

Jordan, you captured exactly what I am trying to do.

No, I did not try Dektol, I thought it is supposed to be very similar to D-19. I read that D-72 is very similar to Dektol. if I normalize the relative amounts of ingredients, I see that the development agents (MQ) and the accelerator have exactly same relative concentration in D-19 and D-72, but the preservative and restrainer are 3 times more concentrated in D-19. I don't know what that means.

 

Patrick, I think the gamma product is still applicable to the LINEAR portion of the overall process. My suspicion, when said "condensed blacks", was that for some reason I am NOT getting LINEAR response. but maybe I am interpreting all that wrong. Is it possible that significant portion of the positive is coming from the non-linear part of the curve? If this is the case, how longer exposure fixes it - with shorter development I get lower gamma, will it help to raise the achievable Dmax?