3.2MM OR ONE EIGHTH OF AN INCH
A Tale of Two Cities or, More Than 3mm
Well, alright, Leighton Buzzard is not technically a City, but Dino does live in Los Angeles. The story runs like this.
Some few months ago, Dino, who curates the Hefner Moving Image archive in LA, mentioned that he had come across some 3mm film stuff, but was lacking a one half of a gate for a projector that had been converted to run it. He wanted to be able to run film for a talk he was due to give in October. Would I be prepared to make a gate for him? Well, this ent really my forte; I tend to get the likes of Nigel Lister to do the tricky bits. Nor did I understand quite why, in the whole of the broad, free land of America there was no longer a single engineer capable of doing tjob. Still, I was reluctant to turn down a friend and, despite some trepidation, didnt say no.
Then nothing happened for a couple months (I think this is the correct American way of saying it), until it suddenly became urgent and a FedEx package arrived. It contained this. The other info I got at the time was that the gate was from a B&H 625-style projector (American Version). That was it. From this I was supposed to imagine and create a front gate for the 3mm film. For a variety of reasons, not least the Argenteuil Film Fair, there were quite strict limits on the time I could actually use for the job before the October deadline, so I felt it too late to duck and pass the job to someone else, and set to.
I naturally pointed out to Dino that an actual sample of the film would be helpful. A second package arrived with some film and part of a gate for a printer that had been developed for the film, with the following comment:- OK so first off I would say please don't change anything on the back part of the gate since that was from the original projector so any modification should only be to the front part so as to fit into the back part....I have something here that I think will help you wrap your brain around the solution...I also have an optical printer that was made in order to blow the 3mm film up to 16mm, I have taken off the front part of that gate and will send it along with the film reel and I am hoping that when you see his solution for the sprung gate on the printer, a light bulb will go off and you will solve it.
It was not until about this stage that I actually discovered what the 3mm film was all about. According to Dino, the system was designed in 1960 by a famous camera designer named Eric Berndt as a special format for NASA to take into space. The idea was they could take tons and tons of these tiny little rolls of film and shoot hours and hours of footage that would take up very little space in the spaceship, then when they came back to Earth they could blow the footage up to 16mm so it could be used easily on all of their existing equipment. In fact this never actually proceeded, so it became a format that never really existed, but I have all of the equipment here in the archive. It included 2 cameras, optical printer (3mm - 16mm), a small rewind bench, many reels of varying sizes, developing equipment, and a projector. The only problem is the projector was missing this front lens/gate assembly. Believe it or not I actually have some film here that he mag striped to test with adding sound.....
The second package confirmed suspicions that had gradually been growing in my mind, so I directly challenged Dino on the true size of the film we were talking about. He replied YOU ARE CORRECT!!! I went digging through some files and found something I had never seen before that gave the following dimensions; Film is 0.125 [one eighth to you and me MAS] inches in width, or about 3.2mm, and picture area is 0.075 x 0.100 inches. Unsurprising, I suppose, for the Americans to use Imperial measurement (tho they didnt for any other film gauge) but at least it explains the Hubble telescope problem.
I tell you all this not to take the Mickey out of Dino (well, not entirely) but to give you some idea of the difficulties I was laboring (American spelling) under and so excuse myself when it all goes wahoonie-shaped.
Here are pix of what I did.
Making this involved making all sorts of assumptions, probably including some I didnt even know I had made. I knew it had arrived in the States, but the only info I got was that the gate didnt lie quite flat on first test. So I was still waiting for any meaningful feedback. I was later told that when held roughly in place all that showed was sprocket holes. Dino then hired a blind man on a galloping horse to make a video (hah!), several seconds of which (most of it was dark screen and wobble) did indeed seem to show this. Closer examination of the pictures I had of the actual machine showed a distressing lack of the framing device provided by the manufacturer to tackle this.
Then I went on holiday for a fortnight. When I got back, the entire machine was waiting for me. Where it was waiting was in a Fedex Depot 20 miles away in the middle of a derelict MoD base pretending to be a Business Park. No comment. Here it is; the odd lump on the back is an extension of the claw pivot to reduce the stroke.
Once I got my hands on the thing, the falsity of some of the assumptions I had been making gradually dawned on me. The main one was that the back gate and claw had been lined up in the same optical axis as for 8mm. No. Take a gander at this pic of an unconverted B&H. The inner edge of the gate channel has two sprung edge guides for the film (there are fixed ones the other side). You can also see these in the sketch I made of the back gate a couple of pages further on. The new gate had been lined up against the sprung guides. The optical centre would be 4mm (half 8) from these guides.
However, the optical centre for a film 3.2mm wide would be only 1.6mm from the edge. Which meant that I had somehow to shift across the gate mounts still on the same lens/gate mount by a whole 2.4mm before the front part of the gate would line up with the back part. And I am here to tell you there ent a lot of space to work with. The existing mounting holes have no surplus material in the direction I needed to go. I spent many hours figuring out what to do and made a considerable false start before arriving at something that looked like it might work. Trouble was, the new sprocket assemblies and especially the sprung edge guides got in the way and I had to cut away a lot of the material that I had added before the gate would shut. Along the way I also discovered that the original gate/lens holder assembly supplied by Dino was the wrong one. I had to cannibalise a machine of mine to get one that would work its a matter of the lugs that engage with the spring clips on the projector body (between the sprockets) that hold the gate shut.
Here are some pix of what I (finally) produced.
You can see, particularly in the first pic, just how far off optical centre the gate has moved, and the lengths to which I had to go to provide some sort of mounting for the gate. I am quite chuffed to be able to report that it actually works and I have shown some 3.2mm film. The film seems quite easy to handle and has made me think once again about getting out the bit of 4.75mm film I have and seeing if I can make that run. Here is a much blown-up image Dino sent me.
However, showing the film demonstrated more of my mistaken assumptions. I made a sketch of the back plate of the gate supplied by Dino. There is a shallow channel down the back plate (not drawn here, but see pic of actual), but it is not, as I just assumed, in the middle (I even sketched it off-centre!) But at least it IS off-centre on the original machine, too. Into this channel is slotted a shallow gate strip, which is held
in place by the (new) fixed edge guide. The gate strip stands slightly proud of the main gate plate, so the reverse of this fixed edge guide has a cut-out where it overlaps the gate strip. Now, in the original machine, the aperture plate is clearly the one in the back part of the gate, and I therefore assumed the aperture in the new gate strip would have been made to be the right size. But it ent. On the screen, I got sprocket hole showing top and bottom. Now, as I had to hand the projector over to Dino within days, there was no way I was getting into any further malarkey at that late stage. So I devised the Stevens Patent Post-Lens Masking Device (PMD). It is designed to be customisable by the user, who simply tapes thin card across the hole in such a way that the edges define the aperture in the desired format. Moving the PMD towards or away from the projector allows exact framing. The PMD comes complete with a sturdy base, with full height and rotary adjustment, plus a precision horizontality adjuster, and is free with every B&H one-eighth inch gauge machine repaired.