Archived posting to the Leica Users Group, 2001/07/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Slobodan- Years ago, I remember that the hydrogen peroxide fuming methed was used with the glass plates used by astronomers, as well. In addition, they mounted the film in a holder that was chilled with either liquid nitrogen or dry ice, but the idea was to cool the film so that the reversal of exposure due to 'reciprocity failure, as it is commonly called was diminished with exposures that could last for hours when exposing deep space objects. It seemed too messy for me, but we used an old Yankee safelight which used to come with a yellow, brown, deep red, and green filters. The green was very dim, and was used for 'visual' inspection of panchromatic emulsions, but was so dim I never was able to master that trick! However, we did expose our Tri-X to it; usually, it was with a 7 1/2 watt bulb, using the green panchromatic filter, and exposing a roll of film for 10 seconds or so at a distance of about 5 feet. Since all film seems to have a 'toe' in the responsive curve that indicates a certain, shall we say- inertia. One can expose the film to a quantity of light, or other radiation, before there is any developable latent image. This is why x-rays are so insidious- the radiation can be cumulative. In the case of flashing, the trick is to give just enought exposure to 'prime' the emulsion so the next few photons will result in a developable spot- sort of like pushing a car... it is hard at first, but over coming the inertia makes it easier to move! even a slight fog will not hurt the image, as it is evenly distributed, and if you are underexposing, and generally overdeveloping, this does seem to help flatten the otherwise contrasty image. You might give it a try- it's an interesting experiment. Dan - ----- Original Message ----- From: "S Dimitrov" <sld@earthlink.net> To: <leica-users@mejac.palo-alto.ca.us> Sent: Tuesday, July 24, 2001 11:01 PM Subject: Re: [Leica] re: digital noctilux vs 10X faster films? > I still have the instructions for hydrogen peroxide fume "bath." I never > tried it, but according to the instructions you can boost Tri-X to > 16,000 ASA, or thereabout. I got it from Rangefinder Magazine years ago > thinking I was going to redefine available light theory and practise. I > never got past first base in that quest. > > Slobodan Dimitrov > > > Daniel Post wrote: > > > > In re the HTML page--- thirty five years ago, we called this "flashing" the > > emulsion- a tenfold increas is about three stops, I don't think we did that > > well, but exposing Tri-X to a green safelight for a few seconds sure did > > inprove the shadow detail of our night-time shots of the high school > > football team!! > > Dan > > t >