HYDROGEN HYPERING for ASTROPHOTOGRAPHY

PART II: HOW TO BUILD IT YOURSELF

Building up a hypering system can be done quite easily if you can find or make or buy the tank. This is the one piece of the system that is hard to locate out in the commercial world. If you want to locate or build the tank, here are the requirements that your tank needs to have in order to be useful: THE CHAMBER:

• 1) LIGHT TIGHT WHEN SEALED !!
  

• 2) Big enough to hold the film you want to hyper. ( 35mm requires only a small container while 120 and 4x5 require much larger systems )

• 3) Able to be sealed tight for vacuum and pressure. ( This is tricky... the best seal is an O-ring groove at the top and bottom of the chamber..The bottom of the chamber can be permanently sealed with a good coating of silicon sealer and some bolts to tighten down the plate after the silicon bead is in place. The top ( removable ) plate needs a good seal with an O-ring and 3+ bolts.)

• 4) Gas and vacuum connections ( Easy .. buy pipe fittings for gas and you can plumb the tank easily. When you put on gas fittings, wrap all male threads with 3 layers of teflon tape before screwing the fitting into place for a good vacuum and pressure seal. )

• 5) Insulate the tank to keep in heat ..(A layer of ensulite wrapped> around the tank and secured with some tie-wraps is a simple solution and it will hold your heater element in place on the outside of the tank.
  

• 6) Pressure and vacuum gauge. ( Inexpensive press/vac gauges can be found in most well supplied hardware and/or auto stores for basic low vacuum and low pressure applications. If you are contemplating a real HIGH VACUUM system then these inexpensive vacuum gauges are only a source of gas leaks and you will need a TC gauge to read out vacuum levels down to 1 micron or less.

HEATING the chamber is the next problem, but it is readily solved. You need some heating tape and some insulation and a means of controlling the temperature. HEATING TAPE:

• OPTION 1: You can buy pipe heating tape at hardware stores especially those who live in places that get cold. These typically have a fixed turn-on that activates the temperature when it gets near freezing... Cut this out of the circuit and resolder the heater wires to an ordinary plug and cord.

• OPTION 2: Heating wire and heating strips and heating blankets are available for pretty reasonable prices from a number of suppliers. OMEGA is a major source of such goodies. Phone: 1-800-TC-OMEGA and you can get a super catalog. This option may be best for building a bigger tank and system but requires a bit of do-it-yourself wiring

• OPTION 1: In AMOACP we describe an easy way to do temperature control using only a voltage control system and a bit of a calibration of temperature v. voltage. This is the least expensive way to go.

• OPTION 2: Very nice and very capable temperature controllers are available today from a number of sources. Again, OMEGA ( 1-800-TC-OMEGA ) is a major source of these goodies. You can probably find these units in most surplus stores but be sure they are working before you lay out your $$$. A microcontroller based temperature controller will cost ~$150+ but you can program these guys to do all the work for you ... They can be programmed for a delayed turn on and to ramp the temperature up and to ramp the temperature down .. and you can even hook them up to cool the chamber off after you are done with your hypering cycle! A temperature controller requires using a temperature sensor. Temperature sensors are also an OMEGA item. The least expensive ( and least accurate ) is a length of Thermocouple wire while the most expensive and most accurate is a platinum thermocouple.
  

Once you have a chamber built and have put together a heating system, you are close to ready for some film hypering. Now you need to dry out the film a bit before you get ready to put the forming gas or hydrogen into the system. You can do this by pulling a low vacuum on the tank using a hand vacuum pump or by using an "inexpensive" mechanical vacuum pump. If you are interested in HIGH VACUUM work, you will be looking at buying a good rotary vacuum pump from Varian or Alcatel or Welch. ( VARIAN sells a very nice book on introductory vacuum work and can be contacted via 1-800-8-VARIAN for a catalog) If you do not want to use a vacuum for this drying out, then you could dry out the film a bit by purging your tank with DRY air or Nitrogen. If you do not do a bit of drying before hypering you will get some extra fog and your final film speed will be lower but you will still have hypered film!


DEFINITIONS:

• LOW VACUUM >= 1 mm pressure (1 mm = 1 Torr)

• MED VACUUM >= 1 micron (1 micron = .001 mm)

• HIGH VACUUM <= .01 micron
  

• LOW VACUUM --> hand pump, single stage mechanical pumps

• MED VACUUM --> 2 stage rotary pumps (or diffusion pumps *DO NOT USE*)

• HI VACUUM --> turbo molecular pumps
  

Finally, you are ready for some GAS for hypering. You can use pure hydrogen (with great care !!) only for Black and White films such as Tech Pan. For color films, Forming Gas is a must or you will find drastic color shifts in your film. Forming Gas is a mixture of Nitrogen and Hydrogen and the typical mixture seen in amateur astronomical workings is a 92% Nitrogen + 8% Hydrogen mixture. All of these gasses are generally available from commercial sources or from welding supply houses. You can order a tank of forming gas ( various size tanks available ) with the mixture of Nitrogen and Hydrogen that you specify for substantially less $$$ than you will find much smaller tanks of FG from the popular supplier for amateur astro hypering.