Color densitometer and pyro negative

[Jimmy Peguet]

Hi all,

How do I read pyro negs on a color densitometer (mine is a Kodak, a rebranded X-Rite) ? Is the pyro reading OK on a color densitometer using the Vis mode, or should I read the blue channel of the RGB mode ? How does it work with different stain colors, e.g. the yellow-green of PMK, or the brown of some pyrocatechin developers ?

Thank you for your answers.

[Jorge]

It should be read on the blue chanel. Usually you will see about a stop difference (0.3) between the red channel and the blue channel. This is a fairly accurate number for regular enlarging paper, for UV sensitive materials like pt or azo the response is not as accurate and you see greater response on the highlights which have more UV blocking response.

The stain color is fairly accurate in the sense that brown negatives have a greater UV blocking response than pyro negs, but both are fairly close.

[Jimmy Peguet]

Thank you , Jorge.

Will this blue channel reading be more or less accurate depending of the strength of the stain (the heavy stain of a pyro neg or of the much lighter one of an ABC neg for example) ?

[Jimmy Peguet]

Ooops. I meant "the heavy stain of a PMK neg".

[Jorge]

The more stain the greater desnity. Yes according to stain the blue chanel will give you more or less accurate density. You should try Pyrocat HD, less overall stain than PMK and less streaking toruble than ABC.

[fhovie]

I read an artical in view camera magazine that suggested that PMK negs should be read in a UV channel. They suggested an X-Rite 361 unit that is used more for graphic arts than for photography. No experience here, just relating what I read. I am not yet sure if I will get a densitometer, but if I did, this is probably the model I would get.

Frank

[Jorge]

Yeah, the 361 would be the best choice. But even on E bay they are going for ridiculous prices, the last one I saw went for $700. The blue channel is good enough for goberment work...:P

[fhovie]

I noticed that - Before the article was written - they were in the 300 range acording to the article - i think the article kicked up the demand - I also bet in six months or so they will come down - I have seen this before - Of course - maybe they won't <G>

[Loose Gravel]

This (BW film/paper spectrometry) is far more complicated that than just using a 361 or a blue filter, but in the same breath let me say that I think many of you are making this more complicated than it needs to be for making good pictures or calibrating PMK negs. Sure, most paper is sensitive to UV...and to blue and to green light. Stained negs block blue and some green more than other colors, so paper 'sees' a stained negative with higher density than a non-stained neg. We, humans, don't see blue light very well and nothing above about 400 nm (violet). We do see green quite well and then falling off in the other direction (red), too. Most glass and lenses don't transmit light past about 350nm, the big exceptions here are flourite lenses and reflective optics.

To precisely measure film density for calibration, one would need to know the spectral response of the paper you are using, the spectral transmission of all materials in the optical enlarging (or contact printing) path (not just the negative, but the lenses, glass carriers, plastic masks, VC filters etc.) and the spectral output of the light source. Once all this stuff is known, it is multiplied and integrated over the spectrum of interest and poof...the answer. Sound hard. It should. It is. And the question is, why bother? Take a picture, develop it, print it and is it too soft or too hard. Adjust development accordingly. Or use some of the calibration techniques in books. This takes care of all the variables in your system. If you must use a densitometer, and I do but I didn't for lots of years, use whatever you can afford. They all work. If the desitometer doesn't have the dynamic range to add a blue filter, just do it without and add 10% to the density. You will be so close that whether you have a 361 or 613 or xyz won't matter.

Take more pictures.

Good luck.

[Jorge]

. If the densitometer doesn't have the dynamic range to add a blue filter, just do it without and add 10% to the density. You will be so close that whether you have a 361 or 613 or xyz won't matter.

Take more pictures.

Good luck.

This is not what my experience shows and it certainly would negate the use of a densitometer as a tool for greater accuracy. In my negatives both developed in pyro or pyrocatechin the stain makes a great difference in the density of the highlights and is certainly greater than 10%. For example negatives developed for a DR of 1.5 for pd printing show in vis light a max density of 1.2 but with the blue channel they show 1.5 sometimes even 1.6. This is 1 stop in exposure and approx 25% of the DR, certainly far greater than 10%.
If one is working with normal enlarging paper, I agree that the UV spectrum makes little difference, in addition enlargers put out very little UV (the reason why they cannot be used for alt processes) which is mainly absorbed by the lens. But if one is working with an alt process or azo, the UV spectrum is very important as it is the part that exposes the medium.
Testing can be made as difficult or as simple as one wants but the more involved testing procedures with use of a densitometer produce the best results. Sensitometry for photographers is not difficult and it certainly produces better results than "take a pic and see what happens" for that I agree you don't need a densitometer, you do however need a lot of money to buy lots of film for the trial and error.