Hints and Kinks

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This is a collection of simple tips and techniques worth sharing.

Darkroom

Optics

Rotating Polarization with Mirrors

PolarizRotateWMirrors.jpg

This image is self explanitory on how to rotate the polarization of the laser beam with two front surface steerable mirrors. This was taken directly from Kaveh's Thesis with his permission.

Silver-halide

Defogging PFG-03

I have successfully killed bad fogging on Slavich plates (without also killing the photosensitivity) by soaking them for exactly 60 seconds in a solution of:

  • 20 g Ferric EDTA
  • 10 g KBr
  • Water to make 1,000 ml

This solution keeps for years. Ferric EDTA is ethylenediaminetetraacetic acid ferric sodium salt. What amazed me was that the photosensitivity of the plates did not drop noticeably afterwards without my needing to resensitise them in say 2% ascorbic acid (vitamin C) at pH ~6.

~Jeff Blythe

Defogger

adapted from the thread http://holoforum.org/forum/viewtopic.php?f=9&t=215

PBU (Phillips - Bjelkhagen Ultimate) bleach makes a good film defogger

  • 10 g Potassium persulfate
  • 10 g Sodium bisulfate (or citric acid)
  • 20 g Potassium bromite
  • 1 g Cupric bromide
  • 1 g Amidol (or Metol)

To use it as defogging solution, pH must be raised first, otherwise the sensitizing dyes will be deactivated. (This is true at least for the PFG-03C dyes.) Diluted it 1:10 parts water, then raise the pH to 5.6 by adding drops of 10% sodium hydroxide. Soak the plates for 1 minute in the solution, then rinse and allow to dry.

DCG

Effect of Overexposure

DCGdiffeff.jpg

adapted from a post by Joe Farina, http://holoforum.org/forum/viewtopic.php?f=7&t=652


Overexposure can have a drastic effect on dichromated gelatin. Test strips early and often are well advised.

The graph is from Lasers and Holography by Mehta and Rampal, 1993. It was reprinted from a paper by Chang and Leonard, "Dichromated gelatin for the fabrication of holographic optical elements," Applied Optics, 1979.


Boiling holograms

Buddha before boiling
Buddha after boiling

adapted from a post by manalokos, http://holoforum.org/forum/viewtopic.php?f=7&t=138


I was frustrated with a hologram of a tiny buddha statue because it was dim and narrow-band, shifting a bit too much to the blue. I heated water until it boiled, took it out of the heat source, and then dropped the plate inside, left it there for 60 seconds, and put it into ambient temp water. I re-developed it, and I got a much more broadband and brighter result.