Category: labnotes

friday: Collected Maybe

Posted on Posted in alt photo, collotype, labnotes

many small readings. short hand notes.

st/ages of theory: how-to / what / why

learning from the hobby lobby means you may never know a reason. you probably won’t ask them questions, after-all, you and they are just hanging onto each other’s opinion. You will never ask where he saw that work. Unless you remember, because you were a member of the academy, you wouldn’t realize that geography was a strong barrier to exhibitions in the 70s and 80s.

Dichromated Gelatin

ask the other camps. look in books and journals. maybe google has a bigger, better memory than you realize.

The advantages of Dichromated Gelatin over Silver Halides are:

  • More efficient recording material.
  • Has less scattering.
  • Is more transparent.

as dichromate is exposed absorption spectra changes.

the broader the exposure spectrum, the deeper the hardening reaction.

characteristics are listed below.

  • Initial thickness of the gelatin layer
  • Initial hardness of the gelatin
  • Concentration of sensitizing dichromate bath
  • Drying conditions: temperature, humidity, and time
  • Exposure, wavelength and energy
  • Time delay between exposure and processing
  • Alkalinity and temperature of processing baths
  • Composition of processing baths
  • Time in processing baths
  • Recording geometry

Factors Influencing Light Geometry

(a) Size of the light source. The larger a source, the greater becomes the angle of light rays travelling from its edges and therefore the degree of undercutting.

(b) Position of the light source. The nearer a light source is to the vacuum frame the greater is its effective size. Conversely if the lamp is moved further away, so its effective size is reduced. It is good practice to increase lamp distance when exposing very fine detail work to reduce the effect of light undercutting if at all practical, (do not forget that the exposure time will have to be adjusted if an integrator is not fitted).

the “printing out” tanning is similar in contrast effect as the “developing out” of tanning developers. DAS / Dichromate systems share the exposure effect: judge by depth of “cure” — tanning, hardening of the colloid. DAS exposure should begin with 365nm wavelength.

Absorbance and sensitivity are different. This is partial explanation for why color of exposing light should be broader with a longer (more depth) exposure requirement.

F-Stop Printing

Posted on Posted in coursenotes, labnotes, the Lab

fstop printing has been used since digital timers entered the darkroom. In 1985 Gene Nocon introduced a timer designed specifically for the f-stop timing method of printing.

In making prints setting a starting point on the timer (and lens aperture) is first estimated. Using prior experience, yours or others, will get you going. All the emulsion makers provided booklets, guides, even calculators that could get you a good start point.

The “step test” is a basic skill shared by all printers. Making this test strip provides visual estimate of print density (exposure) on a single piece of paper. The timing sequence can be in increments of the same amount or in varying amounts. Linear scale printing can make judging intermediate amounts more difficult than fstop method. When dodging / burning, this is harder with a linear scale.

5+5 =10+5 =15+5 =20+5 =25
481632
linear or fstop scale

With split filter printing using fstop timer with 1/4 stop gradation provides most of the control used in exposing BW prints.

Nocon patent June 1985 for timer element. He made use of British government grant money to make the first ones.

He also had a design patent for the key layout. Simple calculator style system with fractional stops .

His patent spends much of its text describing the calculation method.

[https://www.asmp.org/articles/gene-nocon-passes.html ] 404 link

Mr. Nocon, whose photograph of Prince Andrew and Sarah Ferguson was used as the royal wedding commemorative stamp in Great Britain, died after suffering a heart attack Nov. 20 ,2011 at his home in San Diego. He was 65. born on Dec. 26, 1945. lived in London from 1973 to 1990 and earned the Ilford Printer of the Year award in 1980

F-stop Printing

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