I have an ancient home made gas hypering setup. Custom hypering chamber that will hold 6 rolls of 120 or about a dozen rolls of 35mm film canisters. It is insulated and wound with Ni-chrome wire as the heating element. A commercial refrigerator compressor pulls 30 inches of vacuum. A custom built 30V/30A regulated power supply with a thermistor to control the temperature for the heating element. I even have enough forming gas remaining for a few more batches. No need to over-pressurize the chamber with 15PSI + 3PSI and just waste gas. Actually, I have found that 3 PSI yields much better results.
Generally, I have had the best experience by purging the chamber 3 times. 30 inches of vacuum and then raising it to 3 PSI and so on on with air. I preheat the chamber to 120F. Then I purge the chamber and introduce 3 psi forming gas (not 15 psi + 3 psi, but 3 psi above 30 inches of vacuum. Let it sit an hour, drop the pressure to 30 inches, purge the chamber with forming gas to 3 psi, let it sit another hour and then introduce 3 psi forming gas (again, above 30 inches of vacuum, not 15psi +3PSI) and let it sit for the prescribed duration (usually 12-48 hours depending on the film). Finally, I crack the chamber open, quickly load the film into plastic canisters with a small silica gel desiccant packet in each, use electrician's tape to seal them up and off to the refrigerator. I have a sytrofoam organ transplant cooler and I buy dry ice at Walmart and that is how I transport the hypered film to the site. I shoot a frame with an off- axis flashlight to establish the frame boundaries and then shoot every other frame. Humidity will get to the film that is next while shooting the current frame so that is why I only shoot every other frame and then I generally can fit a small desiccant pack or two into the back of the camera when I load the film. Careful - the environment is dry and usually cold so advance/retract the film very slowly so you don't get static discharges. I buy my silica gel dessicant packs on Amazon for cheap. As soon as I have taken my shots, I take another "insurance shot" with an off axis quick flash with a flashlight to create another exposure with frame boundaries, then I slowly withdraw the film back into the canister to avoid static discharges and then back into the plastic film canister with a new desiccant pack and reseal with electrician's tape. Back into the organ transplant cooler and then home. Drop them off at the lab with instructions NOT TO CUT THE NEGATIVE and DO NOT PRINT but the first/last shot with the off axis flashlight usually works even if they cut the negatives because the automated machines detect the frame boundaries and won't cut the negatives with the object, usually the brightest in the frame thinking it is the frame boundary..I return home with the developed negatives, scan them with a 9600 dpi film scanner and then process them just like digital images.
I have had excellent experiences with FUJI 400 professional, sadly no longer available. I used to waste a lot of gas with raising the pressure to 18 PSI, but not at all necessary and my current process always yields better results
BTW, if you are using an OM-1n like I am, best replace all the light seals. They are cheap out of Japan and will keep your OM-1 working for a few more decades. The original seals degenerate into goo and no longer work. The new seals are made of a different material that is less susceptible to aging.
Just what I have learned from taking emulsion astrophotos since the early 80's
I also take a lot of shots with 2 modern Canon DSLR and an ancient STV (updated with IR block RBG filter wheel so it is an ST237A for imaging).
Nothing really, for the price, trumps film for raw resolution. We can banter about sensitivity but when it comes to raw resolution, fine grained films still are far less expensive than high resolution imaging setups - if you can find or afford them.
And, I have found that the old fixed focal length Olympus OM-1 Zuiko lenses are absolutely superb on my Canon DSLR! Inexpensive, absolutely stellar performers and with Live-View, who cares about focus issues. As if you were going to use auto-focus for astroimaging?
Edited by Steven C, 06 July 2019 - 12:27 AM.