Rick's Hypered Techpan and Acros Recipe

What is Hypered Techpan and Acros?

First, Techpan is a black and white film that used to be made by Kodak with ultra high resolution and a good response over the whole visible spectrum, including the very important 656 nm band produced by glowing hydrogen. It is a film favored by amateur and professional astrophotographers, BUT, as in its native state it is useless because it is too slow and suffers reciprocity failure (a nonlinearity in response during long exposures of dim objects). It has been found to respond to a process called hypering or hypersensitizing by throughly drying it and subjecting it to hydrogen gas.

Acros is a film still made by Fuji. It is very fine grain, though coarser than Techpan. It captures all of the visible spectrum except 656 nm. When I make tri-color photos, I use Techpan for the red exposure and Acros for the blue and green. I'm also experimenting with using one sheet of Techpan and one sheet of Acros, both unfiltered, both hypered. I combine the exposures in the computer and tell RegiStar that the Techpan is the red, and the Acros is the blue and green channels. That makes for pictures where the stars are white, and nebulae are red.

Recipe for hypering Techpan and Acros

I've read that everyone who does this has to do some experimentation with his or her own equipment, but we all need a starting place. I've only hypered 4x5 sheet film, never medium format or 35mm. Back when they were available, I bought a Lumicon hypering chamber. They may still be available used. For sure, 4x5 Techpan 4415 is difficult or impossible to obtain at this point. If you have a cache of it, maybe it is still good. I have a little bit dated 2001 and it still seems to work.

Lumicon hypering chamber. The blue hose goes through the wall to the vacuum pump. The chamber came with a heater and thermostat, the dark blue box on the right. I added the insulation over the heater. Forming gas is in tank on left. A vacuum gauge is barely visible behind the tank.

Vacuum

The first stage is to subject the film to a vacuum for a while. Lumicon and some books say you can do this with a hand vacuum pump, and my first tries were by this method. An electric vacuum pump changes the situation dramatically by going to a much greater vacuum, and being able to pull the vacuum over an extended period of time. Some of what follows is speculation, based on partial understanding of the references and some experimentation. Apparently a high vacuum is a very different thing from a pretty good vacuum in that it can really pull the moisture out of the film in a completely different way. If I use the electric two-stage vacuum pump and run it for like ten minutes then close the valves of the chamber and let it sit overnight before putting in the "forming gas" it takes about 72 hours in forming gas to hyper the film. If I instead let the vacuum pump run for 12-24 hours with the valves open to the hypering chamber, I only need 24 hours in the forming gas to achieve a better job of hypering. Here's where my understanding is incomplete, but I think the first way, establishing a vacuum then closing the valves, the vacuum is quickly destroyed by the water that sublimated out of the film, and by the inevitable leaks. The second way, the vacuum is continuously replenished by the pump, and more and more water is pulled out of the film. This is all very strange, because of course the film is dry to start with. But even a milligram of water would be enough to mess up the vacuum. If I pump down the film for 24 hours then put in the forming gas for 72 hours, the film is "over-hypered" and too dark.

Vacuum pump, commonly sold as an air conditioning vacuum pump. A two-stage oil pump. I don't know whether it pumps down to a millitor or a microtor, but it goes way beyond a hand pump.

My procedure as of 2012 is to run the vacuum pump for at least an hour.

Forming Gas

The second stage is the "forming gas". This is a mixture of 8% hydrogen and 92% nitrogen. Lumicon used to sell it, but they don't any more. Lately I've bought it from Mesa Gas. For an explanation of what the hydrogen and nitrogen do, see photographic hypersensitization The chamber is heated to 50 degrees C. After closing off the valve to the vacuum pump, add the forming gas until you are back to 1 atmosphere, or maybe very slightly higher. That would be between 0 and 3 psi on the gauge. I've found that leaving the forming gas in the chamber with the film for 48 hours is about right for Techpan, and 24 hours is good for Acros. If your vacuum system isn't so good, it takes longer, up to 80 hours.

Now here's an area where I have a better understanding: a film grain (crystal of silver halide) is exposed when two photons hit it. If one photon hits it and knocks loose an electron, it is in a quasi-stable state. If a second photon hits the grain then it is really exposed and stable, while if a free electron falls into the hole created by the first photon, then the grain is effectively reset to the ground state. In normal daylight exposure times, like 1/60 second the effect of the free electrons is negligible. But in an astronomical exposure, like 30 minutes or two hours, there might be a significant delay between one photon hitting a grain and the next one. That's because the light is so dim (the photon flux is very low). Hypering the film slows down the flow of free electrons and extends the time that a grain can wait in the quasi-stable state for that second photon. How someone figured that out is way beyond me.

So here you are with a sheet of film that has been sucked dry for 2-24 hours, then dosed with forming gas for 24 to 48 hours. If possible, I take it right out of the hypering chamber and put it into a film holder then put that into my telescope camera; in total darkness, of course! If you can't use it right away, you need to keep it extremely dry. I found some plastic containers used by fishermen for storing tackle. They are gasketed and have four latches on them. With some modifications they hold a film holder just fine, along with a couple of packets of dessicant. Ziplock bags and food storage containers generally are not water/air tight but might do in a pinch. Recently I found out that 4x5 film can move in the film holder so I've taken to orienting the film holder and tapping on it to ensure that the film has settled into the film holder and won't shift during the exposure.

Hypered techpan is similar in speed to E200, if you are used to that, except that it keeps on recording light well past the two or three hours that I found E200 is good for. I've been shooting three exposures of any given object through red, green, and blue filters, called IDAS filters. These are really nice dichroic filters sold by Hutech. I use a home-made camera cobbled together from an ancient 1950's Graflex film holder.

Developing

Developing your masterpiece is the next step. For Techpan I use Kodak HC-110 developer, dilution B, for 12 minutes. For Acros I use Tmax developer, 8 minutes. Then stop for 30 seconds and fix for five minutes in Ilford fixer, mixed to film strength: 1:4. Then I wash it for two minutes in water, two minutes with Perma-Wash, and another two minutes with water in a Jobo processor. For mixing up HC110 dilution B, I found a needle-less syringe that lets me measure 7.8 ml of the thick syrupy developer into 250 ml water, without the intermediate working solution. I first poured the whole bottle of HC110 into four light-tight airtight containers designed to work with the syringe. A drugstore can supply these.

Recipe for Hypered Techpan (4x5 sheet)

  • Put one or more sheets of Techpan into Lumicon hypering chamber, close the lid (all in the dark, of course)
  • Vacuum for 1 hour with 2-stage vacuum pump
  • Fill chamber with 8% hydrogen/92% nitrogen to 0-1 psi, heat to 50 C
  • Leave film in the chamber for 48 hours at 50 C
  • Remove from chamber and put it into film holders
  • Expose, typically 1-3 hours
  • Develop 12 minutes in HC-110 dilution B at 20 C
  • Stop 1 minute, fix 5 minutes, rinse 6 minutes with 2 minutes fixer remover, Fotoflo, air dry
  • Scan, process, share, print...
  • Recipe for Hypered Acros

    Same as above except:
  • Leave film in the chamber for 24 hours at 50 C
  • Develop 8 minutes in Tmax developer
  • References

  • A Manual of Advanced Celestial Photography, Wallis & Provin
  • Wide Field Astrophotography, Exposing the Universe Starting with a Common Camera, Reeves
  • Hypersensitization and Astronomical Use of Kodak Technical Pan Film 2415, Edgar Everhart in AAS Photo-Bulletin No. 24, 1980