Most films suffer from reciprocity failure and are not suitable for astrophotography. After the shutter is opened, the film's ability to collect light continually drops off. This is called reciprocity failure and is one factor that makes most films undesirable for astrophotography. One way to flatten the reciprocity failure curve is to shoot hypersensitized film. Hypersensitizing does NOT increase the speed of the film. It changes the film in such a way that it can continue to collect light longer than it normally would and flattens out the reciprocity failure curve. In other words generally speaking, if the shutter is left open for a 2hr exposure, hyped film should have collected more light than the same film unhypered. Another benefit of hypering film is that during the hypersensitizing process impurities and moisture are removed from the film. Both are causes of reciprocity failure and possible image degradation. None of this is a factor for "normal" photography. But for the astrophotographer, trying to pull out the signal of very dim objects, it's a great benefit. Hypersensitizing is one of the great "secrets" of astrophotography.

You can buy already hyped film from Lumicon , but at around $13 a roll, plus very expensive (and necessary) over night air shipping. For me it's easier to hyper it myself. And I know that the film I'm shooting is freshly hypered. The longest I've gone so far from hypersensitizing to shooting is 1 month. The photo at right shows my Lumicon Model 300 hypering kit. It does a fine job and you can hyper either in the film canister or with the film unwound on a reel inside the pressure chamber. I have only hyped in the film canister. I think hypering on the open reel is more of a necessity to astrophotographers shooting 120 format film. I've always had evenly hyped film leaving it inside the canister.

Lets take a quick look at the components that make up a hypering system. The forming gas is a mixture of 98% nitrogen and 8% hydrogen. You can hyper with pure hydrogen, but you better know what your doing so you don't prematurely end your astrophotography career! The temperature probe is for the thermostat heater control to maintain a constant temperature inside the pressure chamber. A necessity for evenly hyped film.

The procedure I use for hypering film is as follows: Place the film (in the canister) inside the pressure chamber. Heat the chamber up to 50C (122 deg F). Pump the chamber down as far as you can with the hand pump. Mine goes down to around -27psi at 620 ft above Sea Level. Fill with forming gas to -3psi. Let sit in the chamber for 30 min. As the impurities and moisture are removed, you can see the pressure gauge on the chamber rise. Repeat this purge process every 1/2 hour for 2 hours. Pump the chamber down to -27psi one more time. Fill with forming gas up to +3psi. Start timing it. Once the time is up remove it from the chamber and put the canister inside the plastic container it came in with a few crystals of desiccant. Double bag it in zip lock bags and store it in the freezer until ready to shoot. This will maintain the hypering benefit as long as possible. You should be able to store hyped color negative film in the freezer for at least 6 weeks under these conditions. Kodak Technical Pan 2415 can be stored for up to 6 months under the same conditions.

What is the main shortcoming of shooting hypersensitized film? The main problem is the film is so dry that in the cool night air it soaks up moisture like a sponge and can creep inside the camera body ruining your exposure so you will need some system to keep your film dry during exposures. I use a dry air purge system. You can also use a (very expensive) nitrogen purge system. Using some kind of system to keep your film dry during the exposure is not as critical with color negative film as it is with Tech Pan 2415 due to it's very thin negative.

Here are the films and hyper times I have successfully used so far. All inside the film canister.

• Kodak PPF Pro 400 - 6hrs at 50c and +3 Psi
• Kodak PJ400 - 6hrs at 50c and +3 Psi
• Kodak LE400 - 6hrs at 50c and +3 Psi
• Kodak Royal Gold 200 - 2hrs at 50c and +3Psi
• Kodak Royal Gold 200 (New Emulsun) - 12hrs at 50c and +3Psi
• Kodak Technical Pan 2415 - 90 and 95hrs at 50c and +3Psi

It should be noted that all these films except for possibly the RG200 and definetly the Tech Pan Make great astrophotography film off the shelf unhypered and demonstrate good resprosity failure characteristics. PPF Pro, PJ and LE all demonstrate a high red and blue response even unhyped and are great for shooting red Emission Nebula and blue Reflection Nebula. For this reason any of these are my choice for these types of objects. In my opinion RG200 has a more overall balanced color response and is my choice for shooting galaxies which emit light on a full spectrum unlike nebula.

Above all when your hypering your own film......There are no hard and fast rules so keep detailed notes! IT'S WITCHCRAFT! My wife keeps threatening to get me a tall black pointy hat to wear when I'm hypersensitizing my film!