This is topic Century H Heads in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Bernie Anderson Jr (Member # 410) on 04-05-2000, 08:28 PM:
I currently am using Century H heads in an arts center that I work for. This is my problem, I have a tremdous focusing problem in both machines (Yes, hour reel changeover) It's never in focus on the right or the left of the screen but the center is perfect. Any suggestions? I've tried everything and still nothing. I was looking at my Century SA's at my other thearte and started to wonder if the whole gate assembly can be replaced from an "H" to a "SA" gate? IS this possible. It's really frustrating, We're trying to get a film series going after 5 years of it being dead because of anti-film people and the only problem I have is poor focusing.
Posted by Scott Norwood (Member # 30) on 04-05-2000, 09:02 PM:
I don't know about the Century H machines, but you really don't want to know what a Century SA film trap assembly costs. (Hint-they're $700 each, plus $100+ each for the gate assemblies).
Posted by Jon Bartow (Member # 241) on 04-05-2000, 09:52 PM:
The Century H is essentially the same as the SA except for the shutter guard (H has no vent holes). First, I'm assuming the screen is not big enough to warrant a curved screen. Next, is the film traveling through the gate flat or not?(i.e. is the film being pinched by a sticky guide roller or a misaligned guide.) If it is flat then I'm afraid you probably need different lenses. What lenses are you using now?
Post your screen size, throw (Front of lens to screen), the height that the projector is above the center point of the screen and the distance left or right of center that the projector is.
Posted by John Pytlak (Member # 331) on 04-06-2000, 06:02 AM:
Start out by using a good resolution test film like the SMPTE Projector Alignment Film 35-PA (RP40). Rack through focus and observe what happens on the screen. As you move focus, does the focus point sweep across the screen? If so, the film is not perpendicular to the optical axis of the lens. Check the gate and lens mount alignment.
If the focus point spreads out from the center as you rack focus, the film is cupping in the aperture. Try adjusting gate tension, and be sure the film path through the gate is not misaligned or "pinched". Another factor here may be excessive radiant energy or hot spotting in the gate. If the focus improves as you reduce power, heat is likely involved.
Focus will be more of an issue with very short focal length lenses, especially those under about 40mm, because they have less "depth of focus". If you have plenty of light, consider a lens with a smaller f/number or internal stop to get better depth of focus. The newer lenses from Schneider or Isco usually have much better field flatness than older or off-brand lenses. If your lens is over 20 years old, use it for a paperweight, and get a lens of modern design.
If the problem is only in scope, be sure you have adjusted the distance ring on the anamorphic adapter to minimize astigmatism. See the "Focusing Anamorphics" section in the Film-Tech "Tips".
Ideally, you should be able to resolve 80 line pairs per millimetre in the center of the screen, and about 56 in the corners. Anything less than 40 lp/mm is unacceptable.
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Posted by Mark Gulbrandsen (Member # 72) on 04-06-2000, 08:18 AM:
The Model H can be a pain to adjust the trap. The solid curved runners were discontinued in favor of the band style trap assembley(they actually used these on the JJ's for 70mm for a while!). The band style is self equalizing and compensates far better. I always felt the this style of Century trap was one of the best ever designed. You could retrofit them with the SA trap and gate, and dovetail quite reasonably if you can find a dealer that has done alot of Kelmar turrett conversions. Try ICECO in Miami, and Motion PIcture Projection Services in Tulsa. They both probably have quite a few trap assembleys in the parts bins. The Kelmar turett replaces the gate/trap, and dovetail, and lensmount in an SA. You could also install these turrett kits installed on site in your booth. They run around 2500.00 per kit plus labor. There are alot of options here and you could also intstall the model C straight gate as well. They also work very well, but thats as long as you don't have too large of lamphouse running. I really think the best choice is the SA stuff.
Mark
Posted by Tim Reed (Member # 137) on 04-06-2000, 09:52 AM:
Here's a likely solution:Loosen the studio guides and shove them as far apart from each other as they will go, then tighten the screws back down.
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Better Projection Pays!
Posted by Steve Guttag (Member # 268) on 04-06-2000, 04:25 PM:
Bernie:It could be anything...
It can be your lamphouse alignments (less likely but certainly has caused what you describe).
The film is getting pinched in the trap (studio guides, are likely as is crud built up between the guide(s) and runner).
Poor grade lenses, particularly on short focal lengths. If the problem is only on one format, say Scope, then you are closer to your problem. Setting a scope lens is often misunderstood...the Tips section here on Film-Tech tells an excellent way of setting the distance ring. If you are using B&L anamorphs, you have to constantly tighten/loosen the locking ring AS you adjust the distance ring so as to make it just snug until you find the best setting; then tighten securely.
While changing the gates/traps over to the SA style is certainly an option and they will project the film better, it won't necessarily fix your problem. And as others have stated, it can be a bit pricey. Off of the top of my head, you would need the trap, gate, trap bracket, and light shield.
Steve
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"Old projectionists never die, they just changeover!"
Posted by John Wilson (Member # 269) on 04-07-2000, 03:58 AM:
I'm going along with Tim on this one. Your film's being squeezed in sideways in the gate causing it to 'bubble', methinks.
Posted by John Walsh (Member # 168) on 04-07-2000, 09:48 AM:
BOTH machines have the exact same focus problem? I betting on a very short throw with short (and probably older) focal length lenes.In which case, new lenses are needed.
Posted by Bernie Anderson Jr (Member # 410) on 04-07-2000, 06:09 PM:
Just to up date you, since there's so many responses, (thank you by the way). My throw is 100 feet on a moderate keystone with a screen about 35 feet wide. The lenses, yes are old, I don't remember the exact make, but I know they are German. The problem occurs on both machines, one slightly worse than the other. I also get it with scope too but not as bad as the flat. The flat lenses are newer than the scope ones. Lenses are on my list to get when the money comes around. The lamp houses are old Christie verticals. They're in pretty good shape and have been well kept. The thing is that any film that runns through the machine gives the same kind of image, soft on the edges and sharp in the middle. The oldest thing I ran in there was from 1959 and the newest was some trailers from a couple months ago and I had the same focus problem on both. The one tech I had look at it said that there wasn't enough tension in the gate. we tightend the spring in the gate knob, it was hardly holding the gate closed and still the same focus, even when I played with pressure adjustments you don't really see any variation. To me it seems like the film isn't sitting flat in the gate. Any thoughts?
Posted by Aaron Sisemore (Member # 145) on 04-07-2000, 07:41 PM:
I have had problems with focusinjg with Century H (curved gate) machines as well, the enclosed trap on the H has a VERY bad habit of collecting shedded polyester dust, causing it to become compacted against the trap rails, eventually causing the focus to suffer, in most cases to the point of unwatchability! The cure is to remove the gate shoe and then chip away the poly dust compactions with a screwdriver or other object that will do the trick then put the trap back together, rethread, and go.... In some instances I have had to do this THREE TO FOUR TIMES A SINGLE SHOW! After enduring countless pissed-off customers and headaches, I demanded the heads be retrofitted with SA traps and shoes. I have *NEVER* had a problem since. and will avoid ever uing a Century H curved gate machine again...Aaron
Posted by Bernie Anderson Jr (Member # 410) on 04-07-2000, 07:59 PM:
The SA trap and gate (assembly) with work by just swaping out the parts? Everything will line up with out a problem? When I took the SA gate apart on one of my temporary projectors (2 years as a temp. replacement) at work I noticed that the gate was similar in the way it mounted in both projectors. Other than the new kelmar turrit conversion kit that I hear good things about, how much would new or used parts cost to convert it?
Posted by Aaron Sisemore (Member # 145) on 04-08-2000, 09:38 PM:
Bernie said:
"The SA trap and gate (assembly) with work by just swaping out the parts? "Yes. I have done it to one of the very troublesome H heads in one of our booths. The only thing that will be required to do will be to cut new aperture plates, as the SA trap seems to have a slightly different centerpoint in the aperture plate slot.
" Other than the new kelmar turrit conversion kit that I hear good things about, how much would new or used parts cost to convert it?"
A new gate/trap assembly, complete with one undersize flat aperture plate cost us about $700. You will also need an SA-style light shield for behind the gate and aperture plates for any other formats you intend on showing on that machine.Used should be much less, and I am not sure of the Kelmar turret kit's price.
Good Luck!
Aaron
Posted by John Walsh (Member # 168) on 04-08-2000, 11:12 PM:
"My throw is 100 feet on a moderate keystone with a screen about 35 feet wide."What is the angle? I mean, is this a "classic" old theater with a steep angle?
Posted by Bernie Anderson Jr (Member # 410) on 04-09-2000, 08:05 AM:
Yes, the place was buid in 1927 and was restored back to it's original interior in 1990
Posted by John Walsh (Member # 168) on 04-09-2000, 09:27 PM:
quote:
Originally posted by John Walsh:
Well, you know what I'm thinking; the angle is a very steep. Is there any way you could measure both the distance from the projector to the bottom of the screen, and again to the top of the screen?If the focus problem is caused by the steep angle, there are some tricks to lessen the problem. One is that off-set lens thing- goto;
http://www.iscooptic.de/catalog/accessories_eng.shtml
Look at the "PC-Cine Adapter"
Another is to tilt the top of the screen frame back to get less of an angle. I've seen many older theaters do this.
The problem could also be reduced by shifting the gate and trap, but this would take a lot of careful work with test film, so I don't really suggest it unless there's just no other option.
I used to work near the Hess buliding on Rt.9, breathing in the wonderful smells of the refinery a bit north on I95.
Posted by Tim Reed (Member # 137) on 04-10-2000, 03:16 PM:
(PFUHHH! PFUHHH! --tap tap tap-- Is this thing on?)Bernie, if the film looks like it's not sitting flat (laterally) in the gate, THAT would be side pressure from the studio guides. You have to loosen them and shove them away from each other, so they don't contact the film.
It's possible that someone took the traps from both machines apart (to clean them or whatever), and didn't pay attention when they put them back together.
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Better Projection Pays!
Posted by Bernie Anderson Jr (Member # 410) on 04-10-2000, 09:32 PM:
I was thinking that too. As long as I've been there I've had this problem and I've never played with them before. Are there much play in the studio guides that they can move apart like that?
Posted by John Wilson (Member # 269) on 04-14-2000, 03:49 AM:
quote:
Originally posted by Bernie Anderson Jr:
I was thinking that too. As long as I've been there I've had this problem and I've never played with them before.?
So, it's been there as long as you have and you've not touched them...
Just move em out Bernie. It's an easy thing to do and I'm still with Tim. I'm 99% sure this is your problem.
(PFUHHH! PFUHHH! --tap tap tap-- Is this thing on?) Love it, Tim.
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"It's not the years honey, it's the mileage".
Indiana Jones.
Posted by Bernie Anderson Jr (Member # 410) on 04-14-2000, 09:03 AM:
I know it sounds strange, but it's very hard to get the screen down and work on the machines. There's always something happening on stage, either they're building something or something's in the way that the screen can't come down. The little time, I've had to play with it when I had the time is usually an hour before a show.
Posted by Tim Reed (Member # 137) on 04-14-2000, 11:01 AM:
John: 
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Better Projection Pays!
Posted by John Wilson (Member # 269) on 04-15-2000, 01:44 AM:
Tim: You Betcha!
Posted by John Wilson (Member # 269) on 04-26-2000, 10:04 PM:
So, Bernie... what was the outcome?------------------
"It's not the years honey, it's the mileage".
Indiana Jones.
Posted by Bernie Anderson Jr (Member # 410) on 04-27-2000, 12:36 PM:
Well, to be honest, I haven't had the time to play with the projectors yet. I currently took over Thursday nights at a new theatre, so between school and my regular shift I just haven't had the chance to get to the other theatre to play with them. But this coming week I'm showing "Some Like It Hot" and "A Night At The Opera" So I'll get to play with them this week.Bernie
Posted by John Wilson (Member # 269) on 06-09-2000, 10:37 PM:
Hi Bernie 
It's been a couple of months now since you first raised this topic and I'm curious.
How did you go? Is it fixed?