Thicker or thinner Film stock?

[Osi Osgood]

I hadn't really thought a lot about it before, but I would assume that a thinner film stock would be better, as it would allow for more clearance or room for the film stock and less potential contact with either sides of the film gate, but that is an assumption on my part. Your views?

[Ed Gordon]

Osi, that is an interesting question. My assumption is that the film gate assembly has been adjusted to produce a steady image with a minimum tension on the film. If anything, I would expect a projector that has been "tuned" to run a thicker film stock would be more prone to project an unsteady image when projecting a thinner film.

Then again, as the saying goes, “ When you assume, you make an ass out of u and me.”

A professional projectionist could probably give us a definitive answer to the question.

[Lee McCaffrey]

The thickness of the base makes no difference to the clearance at the gate, it is sprung to contact the edges at all times and the pressure plate will move in/out depending on the thickness. So it will be in the same position relative to the film's surfaces at all times

[Winbert Hutahaean]

Thicker is acid while thinner is poly. Acid will be affected by VS later on, poly is not. So I would prefer with thinner stock.

[Winbert Hutahaean]

Thicker is acetate based while thinner is poly. Acetate will be affected by VS later on, poly is not. So I would prefer with thinner stock.

[Steve Lee]

I remember back in the day when the industry went over from Acetate to Polyester that there was no need for any adjustments to the pressure on the film slate, as this didn't happen overnight. One week you could be running acetate the next polyester. But polyester does have some issues.

This shouldn't send shockwaves through the super 8 /16mm world, as I can not imagine anyone is running a print three or four times a day seven days a week. But when polyester is used like this it will start to decompose. We would receive a brand new print, and by the end of the first week start to notice a pink dust over the machines. by the end of the second week there would be what resembles hair around the back of the sprockets, gate and soundhead, so much so that it was necessary to vacuum the entire mech out between shows. This was ok with a film that would be shown for two or three weeks, but the problem was if you had a hit movie on your hands.

I remember showing Chicago for over two months, by about the sixth week we no Dolby digital soundtrack left on the print, being positioned between the sprocket holes and getting most of the ware, resulting in having to run the film in optical analog stereo for the rest of the run.

But this only happens when polyester is run over and over again. Ironically polyester decomposes when it is continuously flexed backwards and forwards eg: through a projector mach. What were they thinking of !

[Tom Photiou]

I was talking to Bill Parsons a number of years ago regarding the problems of wow and flutter, particularly on the Elmo ST1200 range, as well as other machines. He reminded me that these projectors were designed when film stock was acetate, long before the thinner film stocks came out so all our machines were designed with the adjustments for acetate.
When polyester stock came out, most machines were fine but as time moved on and people serviced and adjusted their projectors, a few problems were highlighted.

Kevin Brown also had a similar conversation with me a couple of years ago regarding the noise through the gate on 16mm Eiki's. He also explained that if you adjusted the projectors gates/pressure plates using an acetate film, you may find that when you try a polyester film the image may be unstable or vice versa.
The newer poly stock is a lot thinner, and older projectors with worn parts will not be so tolerant when viewing. Kevin and Bill both said it can often be frustrating getting those fine adjustments on some projectors, in some cases hours and hours spent to get the machine do show a steady image or equally, to get the gate noise correct for both stocks.

[Osi Osgood]

All fascinating comments. It does seem that the thinner stock would have more clearance, but, having more clearance, more potential vibration when projected?

[Tom Photiou]

With thinner film, the pressure pads etc will not have the same clearance's and "may" cause problems such as wow and flutter if the pressure isn't enough through the sound drum. Same with the gate, if the pressure plates are slightly worn, as time goes on, our projectors will wear and these problems may become more evident with different film stocks.
Some people may tackle adjustments of the gates, in particular on 16mm machines, i know only too well the consequences of this, i messed up my Eiki SL2, there was no way i could get that adjustment corrected. Acetate film sounded like a machine gun in the gate, polyester was fine for 200ft or so before becoming very noisy. I had to send it off to a professional with the right equipment to set it up. As Kevin Brown explained, trying to get the adjustment correct to ensure a steady image, full focus and a quite transport, is a very long process for a 40 year old projector, and even older ones especially with no new spares available. The adjustment has to take into consideration the expansion in the gates metals as it get hot.
The tolerances on 8mm machines must try the patience of a saint when trying to set these up.
I was very lucky with one of my Elmo's, a few years before Bill retired it developed a slight shake on the image of a number of films. As it happened, the gate was worn, Bill had a second hand one and fitted it along with one of the green guides within the gate. The result was perfect.
As he said at the time, no two machines are ever the same. My original one is one of the quietest 1200HD's Bill had seen, some films will work perfect on one HD, (or Bauer, or Eumig or any other make), but on another projector, same make same model, it will be a problem for some films.

The thinner and thicker films must make projector maintenance, a little more difficult to get right.

[Brian Fretwell]

The other problem is that, with a front sprung pressure plate focus will differ from thin to thick base so mixing them on one reel will need constant refocusing as the distance of the emulsion will vary. A rear pressure plate machine will not suffer from this.