Re: Determining SPT with gum Was: Gums a la Demachy and Puyo

From: Katharine Thayer <kthayer_at_pacifier.com>
Date: Fri, 14 Jul 2006 09:20:54 -0700
Message-id: <7E362F41-E9E0-4637-9EDD-2D5B1C7DE625@pacifier.com>

Mark, this is related to the point I was making re gum. For many
reasons, the "natural" exposure times for gum emulsions will vary
widely, even given the same light source and other protocol. Setting
an arbitrary exposure time, whether you set it at the median of the
distribution of exposure times or at the lower end, as it seems
you're suggesting here for another process, some emulsions just
aren't going to be comfortable with the arbitrary exposure time. The
farther the "natural" exposure time is from the arbitrarily-chosen
"standard printing time" the more awkward and extreme curve will be
required to make that emulsion print a reasonable print in the
unnatural exposure time. And I guess I don't see why that makes sense.

Katharine

On Jul 13, 2006, at 1:44 PM, Ender100@aol.com wrote:

> Hi Chris,
>
> I would agree that people often over expose.
>
> One cause of this that sometimes occurs when determining the
> Standard Printing Time for Palladium is humidity. I am referring
> both to the Relative Humidity of the environment and the amount of
> moisture that goes into the paper from coating and finally the
> amount of time the coated paper is allowed to dry. All these
> factors for a given paper will have an effect. Also there will be
> issues like different papers with different thicknesses, etc.
>
> With higher humidity, which for me begins around 65%+, I experience
> more printing out and self masking with Palladium. When this
> occurs, you can double a standard printing time and still not get
> merged steps, when you would expect 4 merged steps on a 31 step
> tablet. When this occurs, one can examine the steps and pick one
> which gives a "acceptable Black" and use that as the Standard
> Printing TIme.
>
> The reason this is important in calibration, is that you can end up
> with a lot of the tones of your negative getting pushed into the
> deep shadows with little seperation. Then, the curve you will
> derive will be much more drastic to compensate for this and open up
> the shadows. Backing off exposure to a reasonable Standard
> Printing Time will prevent this.
>
> Best Wishes,
> Mark Nelson
> To NSA: When you read this email, would you please search your
> database for my other black sock?
> Precision Digital Negatives--The Book
> PDNPrint Forum at Yahoo Groups
> www.MarkINelsonPhoto.com
>
>
>
> In a message dated 7/13/06 1:48:48 PM, zphoto@montananet writes:
>
>
>> Very interesting....
>> I do find that the number one error with a long tonal scale
>> process is
>> choosing an exposure time that is too long. Salt and pt/pd are
>> killers that
>> way, as well as the iron processes in general. It is almost
>> easier when
>> doing ones that have solarization because you know you don't want
>> that
>> losing density and you make sure to stop short of that...I just
>> choose the
>> one that looks visually dmaxed enough and has not solarized--
>> usually the
>> step right before solarization. It seems that your method with
>> lab will
>> achieve the same results with the scanner, in effect, "seeing" the
>> blackest
>> black with the scanner..but with whatever method, the print is the
>> proof of
>> the process working or not.
>>
>> I remember first going through the calibration process--I would
>> find that
>> the eye could see the minutest differences in density! But
>> exposing to the
>> point of not being able to see that difference is way too over. I
>> think the
>> eye sees like maybe .01 difference or something like that. I
>> imagine the
>> scanner is accurate, too, seeing 0-255.
>> Chris
>
>
>
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>
Received on 07/14/06-10:19:57 AM Z

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