[alt-photo] Re: Your Approach to Making Negs for Platinum Printing? Ideal Negative Contrast and Dmax?
fdfragomeni at gmail.com
Sat Oct 8 21:29:02 GMT 2011
Wow! Thanks for all for all of the info. I'm only working with large format
negatives (I shoot 8x10 and larger) in this case so my follow up is in
regard to what you posted regarding in-camera negatives and not the extra
"Below are some observations I have made in the past (you will find others
in the list archives, from me and others). For the traditional Pt process,
you want a negative with a density range ("DR") of 2.0 or higher (I
generally aim for 2.4) to get both Dmin and Dmax in the print. Note that
not all films available today will produce such a DR, no matter how you
expose and develop them.
BTW, I encourage everyone to stop speaking of "stops" and "contrast range"
-- much better to identify clearly what you mean and speak of "exposure
scale" ("ES") and "density range" ("DR"), to make sure we are always keeping
the distinction in mind. On this, see my message of 11 Oct 2009, in the
archive. For example, while the ES of traditional Pt is around 2.1 to 2.4
(and, therefore, a negative that produces a full-scale Pt print will have a
DR of 2.1 to 2.4), the full-scale DR of the Pt print itself is much lower --
only 1.4 to 1.7 (the latter only with heroic efforts)."
I definitely agree with what you're saying. I often get confused with all of
the different terminology. When you say DR do you mean the range between
FB+F and the most dense tone in the negative? I have a X-Rite transmission
and reflection densitometer at home and I'm unsure of how to read a neg to
determine is DR or a prints ER. Is it simply reading most dense area and the
least dense area and taking the difference? My processes are always much
more visual then technical but I'd like to grasp an understanding of how to
make all of these measurements so that I can empirically understand what I'm
visually seeing and doing.
I am specifically interested in figuring out how to properly measure the
density range in a negative so that I can match my visual understanding of
what these negatives look like to the actual measurement of the negatives
density range. I hope that makes sense. I suppose I'm just looking for a
little clarification on the best practices for using a densitometer and how
to relate the measurements to density range and exposure scale.
Thanks so much for the help!
> Francesco wrote:
> Now that I'm
>> venturing fairly aggressively into platinum, I'm very interested in
>> how you all approach making your negatives for platinum. I'm speaking
>> specifically about in-camera negatives (no digital negs or other processes
>> here). Achieving the ideal contrast for platinum is what I'm interested
>> For silver, a negative with a contrast range of around 3.5 stops will
>> well on a grade 2 filter or paper. There is also a ideal negative dmax
>> some people use as a standard to shoot for but I'm not sure what that
>> is. As I understand it, platinum calls for greater contrast to take
>> advantage of the longer tonal range of the platinum process.
> Below are some observations I have made in the past (you will find others
> in the list archives, from me and others). For the traditional Pt process,
> you want a negative with a density range ("DR") of 2.0 or higher (I
> generally aim for 2.4) to get both Dmin and Dmax in the print. Note that
> not all films available today will produce such a DR, no matter how you
> expose and develop them.
> BTW, I encourage everyone to stop speaking of "stops" and "contrast range"
> -- much better to identify clearly what you mean and speak of "exposure
> scale" ("ES") and "density range" ("DR"), to make sure we are always keeping
> the distinction in mind. On this, see my message of 11 Oct 2009, in the
> archive. For example, while the ES of traditional Pt is around 2.1 to 2.4
> (and, therefore, a negative that produces a full-scale Pt print will have a
> DR of 2.1 to 2.4), the full-scale DR of the Pt print itself is much lower --
> only 1.4 to 1.7 (the latter only with heroic efforts).
> There are two things at work here: (i) matching the negative density range
>> ("DR") to the printing exposure scale ("ES"); and (ii) the character of the
>> exposure scale, however long or short it is. If the DR of your negs is too
>> short to match the printing ES, you'll get low-contrast prints with murky
>> (but not very deep) shadows and/or fogged-looking highlights. But even if
>> the negs have the right DR for the process, the characteristic curve of the
>> printing process may be ugly.
>> The standard long-scale Pt process has a very, very long linear scale with
>> symmetrical, gently rounded toe and shoulder, typically printing the whole
>> step wedge with some scale left over. Therefore, you need to use negatives
>> with a very high DR to obtain all of the available print zones with this
>> process. Photographers have not typically made negatives this "bulletproof"
>> since the late 19th Century, so folks have tried a number of different
>> methods to shorten the Pt exposure scale (adding dichromates, hydrogen
>> peroxide, etc., etc.). These tricks shorten the exposure scale by raising
>> the threshold exposure -- not really a very promising way to go about it.
>> Anybody who has done serious sensitometry with the process has seen the
>> ugly characteristic curves the short-scale versions of the Pt process
>> produce. I have yet to see prints made using any short-scale Pt process
>> that came close to the look of "real" (long-scale) Pt prints.
>> Unfortunately, so many workers are using the short-scale processes now that
>> many people don't even know what a good Pt print is supposed to look like.
>> I commend to you an experiment: Make some in-camera negatives with a DR
>> above 2.1 (try to hit 2.4 for starters), and print them using the standard
>> full-scale Pt process. I bet you never go back to digi-neg Pt printing
>> again, and depending on how big you think prints need to be, that you
>> acquire one or more LARGE format cameras or learn to make good enlarged
>> negatives in the darkroom (not so easy now that slow, blue-sensitive copy
>> films are long gone). If you have no option besides digital, have a service
>> bureau make some 2.4 DR negatives with an imagesetter using your files.
> Think of it as mapping. The scene you photograph has a certain range of
>> luminance values. You want to translate, or "map," these luminance values
>> to useful negative densities, which can in turn be mapped to the available
>> reflection densities of your chosen printing medium.
>> To do this, we start with the exposure scale ("ES") of the printing
>> medium. Using calibrated step wedges, we see what range of exposures gives
>> the full range of printed tones the medium is capable of producing -- any
>> more exposure is indistinguishable from the blackest tone, and any less
>> exposure is indistinguishable from the lightest tone (paper white, or close
>> to it). Now, if we want the full range of tones the process is capable of
>> producing to be represented in our print [which may not always be the case],
>> we know that our negative must have a density range ("DR") equal to the
>> printing medium's ES. So, we arrange to translate the luminance values in
>> the scene to the particular negative densities that will produce the print
>> tones we want to represent each scene luminance value.
>> Not so long ago, we did this by adjusting our exposure and film
>> development, and then perhaps reducing or intensifying the negative or
>> masking it for printing, and finally by dodging and burning as we printed.
>> It sometimes took all that, because we have to condense or compress the
>> 1,000,000:1 luminance range of the scene we photographed (this is about
>> normal for a sunlit scene) down to the 100:1 (or less) density range that a
>> print can reproduce.
>> These days, people who print digitally can use Photoshop to adjust the
>> mapping from the as-captured (or as-scanned) image file to the negative that
>> will be used to make the print. This is much easier, and also much more
>> flexible, than doing it chemically or with masks. However, the goal is the
>> same -- to translate or map certain luminance values in the scene to the
>> desired print density values, using the negative as an intermediary.
>> Applying curves is how we do this. It's fundamentally the same as using
>> the Photoshop tonal controls (levels, brightness/contrast, whatever) to
>> adjust a digital capture for the desired print values (i.e., if you are just
>> printing digital images on paper), with two added wrinkles: (i) you have to
>> understand how the characteristic curve of the printing process responds to
>> the negative values, and (ii) you have to be able to imagine how to "do it
>> in reverse" since you are working on a negative -- if you want the shadows
>> to have more contrast in the print, you have to increase the contrast in the
>> lightest parts of the negative.
>> In theory, you can map any scene luminance value (or digital
>> representation of a scene luminance value) to any available print tone (with
>> the caveat that the curve should be monotonic -- never reversing slope --
>> unless you are after special effects reminiscent of the Sabattier effect).
>> In my view, there is no substitute for learning enough
>> sensitometry/densitometry to really understand how the mapping works, and
>> then to test your processes to see how they distort the mapping so you can
>> correct for it. It's not very difficult, and once it is mastered you will
>> truly have the chops to get what you want out of your photographs.
>> So, all that said, back to curves destroying negative content. Mapping is
>> mapping -- the person who wants to represent the surface of the earth on a
>> flat surface has choices to make, because there is no way to linearly
>> reproduce the surface of a sphere on a flat surface. And as we learned in
>> grade school, cartographers have come up with hundreds of different ways to
>> do it, each one good for some particular task. If you want to be able to
>> visualize comparative land areas, you use a different projection than if you
>> want to determine bearings from one place to another. The same is true for
>> mapping tonal values in photography. So, the "right" curve is the one that
>> produces the results you want -- i.e., the one that maps the scene luminance
>> values to the print densities you want. In general, one way I'd advise
>> folks NOT to do this is to copy someone else's curve "because you're using
>> the same process." No two people ever use the "same" alt process, because
>> there are way too many variables to control. And no two monitors are the
>> same, or scanners, or printers, or Pt "emulsions," or coating techniques, or
>> anything else you use to make prints. So, the only way to end up with a
>> useful curve for your process flow is to test and figure it out for
>> Generally, one would like to calibrate one's monitor, then build a curve
>> for each printing process one uses so one can just adjust the image on the
>> monitor (as a positive), then let the computer figure out what negative
>> densities are required to map the monitor view to the final print (though
>> once again, the monitor has a considerably greater luminance range than a
>> print has density range, so it will be a "rendition" of the monitor image,
>> not a literal copy). Only you can build such a curve, after doing the
>> sensitometry/densitometry on your equipment and printing processes. There
>> are aids available, but IMO one is much better off gaining an understanding
>> of the fundamentals and just doing it -- just as people who really
>> understood what they were doing always got better results than people who
>> "learned" the "zone" system by rote.
>> So, if you have a curve that really does translate (transliterate ??) from
>> your monitor to your prints, great -- it is not destroying anything, but
>> rather helping you to map values from your digital image file to the final
>> print, thereby allowing you to do your image adjustment by eye rather than
>> by figuring. But if your curve doesn't produce prints that are pleasingly
>> rendered based on the screen image, you need to change something. You can
>> futz around with the process to try to match it to the curve you have, but
>> that's the hard way (and you may well not ever find a variation that works
>> as you'd like). Better to adjust your printing process until you get the
>> most linear scale you can (for reasons I won't go into here, having to do
>> with producing the smoothest tonal range), then developing a curve that
>> translates from your monitor to your prints.
>> The problem with the "short-scale" versions of Pt is that they have much
>> less linear tonal ranges than long-scale Pt. You can successfully map this,
>> if you work at it, and thereby get correct overall tonal rendering by using
>> a curve that compensates for the nonlinearity. However, you still won't get
>> the smooth transitions that long-scale Pt can produce. And since the
>> gorgeous tonal rendering is the real draw of Pt in the first place, why
>> settle for something less just because one would prefer to avoid dealing
>> with how to make digital negatives of sufficient DR? Particularly given the
>> cost of the Pt process, I just can't see why one wouldn't use it to its full
>> advantage -- which IMO requires using the long-scale process.
> Best regards,
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