Film-Tech Forum ARCHIVE: Strange Century H Focus probem

This is topic Strange Century H Focus probem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Fred Georges (Member # 505) on 03-04-2003, 08:37 PM:

This past weekend an Art Center I finished installing had it's maiden voyage. A film fest with 4 features (3-1:85 & 1-1:37)The final show went south due to a bad focus issue (Of course with several influential film critics in attendance) The problem was reported to me as a large almond shapped area of the film that would drift severely out of focus. The operater stopped the film several times and checked the gate as well as the lens and the problem persisted. I was NOT there. Upon hearing the tale I went to the theater and checked out the machine (Century Model "H" freshly rebuilt).Running RP-35 the image is Rock steady with excellent focus center to edge & edge to edge (90mm ISCO Ultra for 1:37) I then suspected a heat damaged print so I made up the whole Damn thing and watched it. Except for some minor base scratching the print was in very good condition and exhibited NO focus drift from start to finish. The lamphouse (Christie CL 20 with a strong reflector) has a nice flat field with no hotspotting (The 1:85 shows looked fine) I've tried to duplicate the conditions (Loose lense collar, leaving the gate not fully closed) to no avail. I'm calling it "operator error" but, what did He do??

Posted by John Walsh (Member # 168) on 03-04-2003, 08:48 PM:

Is it possible there was some emulsion build-up, (perhaps from improper threading) which he later cleaned out of the gate/trap?

How experienced is the operator? Would he know enough to accurately describe the problem? The reason I ask is: a person I know put in an anamorphic lens (for a flat film) but described it has being out of focus.

Posted by Jon Bartow (Member # 241) on 03-04-2003, 08:58 PM:

You say the final show went south. Does the lamphouse have a heat filter in it? Does the projector have a water cooled gate? What size lamp is it? How close together were the shows? Did the lamphouse get a chance to cool off between shows? Any chance of air blowing on the gate (booth door or porthole open?

Posted by Fred Georges (Member # 505) on 03-04-2003, 09:01 PM:

Thanks for the thoughtful reply John. The young man in question is one of the staff projectionists (35mm) at a major University here in Chicago. He comes off as knowledgable and I'm sure He used all of his skill to try and rectify the problem. I need to know the cause ( if machine related) to prevent any similar occurrance in the future But, I still think it was something screwy He did.

Posted by Fred Georges (Member # 505) on 03-04-2003, 09:06 PM:

Thanks Jon, 2K Lamp, Dichoric reflector, only show of the day. ALL other formats fine. Extra blower on lamp seal not causing gate turbulence.

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-04-2003, 09:30 PM:

Thanks!

Posted by Fred Georges (Member # 505) on 03-04-2003, 10:04 PM:

Dear Daryl, I actually made two seperate responses to two seperate replys at different times. Should I have edited my second response into my first reply? Let me know and I'll correct it in the future (or now if you wish). Thanks

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-04-2003, 10:39 PM:

No problem Fred! It is prefered that you keep replies in the same post if the replies are within a couple hours of each other. Just reference whoever's name to each part of your reply to make it clear who your replying to.

There's many reasons for it... faster for dial-up users (they don't have to download more pages than necessary), it looks nicer, and it costs Brad less on his bandwidth bills (since each reply has a certain amount of 'extra code').

Leave it as it is, just remember to use the edit feature in the future.

Thanks again,

Daryl

Oh yeah... don't forget to send in a photo of yourself! [Smile]

Posted by Ray Bernardi (Member # 1615) on 03-05-2003, 04:09 PM:

Maybe you had a bug walking around on the lens!

Posted by Mark Gulbrandsen (Member # 72) on 03-05-2003, 06:42 PM:

Fred, The best thing to do is throw the H gates and traps in the garbage and rummage around for a pair of SA gates and traps. Century only made those H's for about three years and discontinued them in favor of the Band style SA trap as it is auto equalizing. Get some crud buildup in an H and you're dead in the water till you clean it out, while an SA trap will compensate for it unless its boulder sized. Also, unless you set the side guides of an H trap very accurately they can cause focus problems of their own, sometimes by causing the film to cup while its running. This is what may have been happenning to you. Many dealers have tons of SA traps and gates laying around for a song and a dance as they come out for good with the installation of Kelmar Turretts.
Mark @ CLACO

Posted by Scott Norwood (Member # 30) on 03-05-2003, 08:27 PM:

Having never seen an "H" in person, I must ask what, exactly, is the difference between the Century SA and Century H? Surely it must be more than just the gate/trap design, as the Centurys ("MSA/2" according to the nameplate) at the Williamsburg Theatre used to have H-style traps (which were basically just curved versions of the C-style trap). Older JJs have this type of trap as well.

Posted by Fred Georges (Member # 505) on 03-05-2003, 09:39 PM:

Dear Mark, I considered the upgrade to an SA style gate & trap but was seduced by the phenomenal picture steadiness this particular head exhibits. Still, after 3 days of trying every trick in the book to duplicate the problem without success I'm starting to believe it is a gate/trap design flaw that reared it's ugly head. To Scott, I have several SA Heads and the only differance I can see between it and the "H" is the gate/trap design & lens shift capability of the SA . Thanks for all the helpfull replys gentleman, A gate/trap switchout is on the Horizon as soon as the Art center can afford it.

[ 03-06-2003, 09:44 AM: Message edited by: Fred Georges ]

Posted by Mark Gulbrandsen (Member # 72) on 03-05-2003, 11:17 PM:

Fred,
The SA stuff properly set up will yield a better picture, and as steady. The critical part of the SA thingy is that the runners are in excellent shape to keep the film from wandering about them....Even better use a pair of JJ heads for unparalled 35mm presentation......
Mark

Posted by Christopher Seo (Member # 7) on 03-08-2003, 10:33 AM:

How similar is the H to the C? I just had a problem last night on a Century C with the film popping in and out of focus-- literally, it was instantly switching back and forth between sharp and blurry over most of the screen, at random. (The print has been running for 8 weeks without problems.) I discovered some hardened buildup, nearly impossible to see, tucked away along the inside of one of the studio guides. It wasn't a huge amount compared to what you can find after one pass through some projectors, but was it possibly enough to pinch the film and pop it in and out of the focal plane? I have never seen that sort of problem before.

Posted by Mark Gulbrandsen (Member # 72) on 03-08-2003, 03:34 PM:

Chris,
There are big differences in the two models but the buildup that you found is most likely the cause of the popping of focus. The H uses a solid Curved gate and trap and the SA main frame and movement, while the C uses a solid straight gate and smaller movement. There are two versions of the straight gate too, but most have solid one piece pressure plates. Some older models had split pressure pads like the Simplex straight gate had.

The older cast iron C's are probably the best American made projector in existance though. Also, some C's were retrofited with H gates and traps for improved focus with large lamp houses. The SA gate and trap can also be installed into a C with only a amall bit of work. The gear trains in all Centurys are virtually the same though.
Mark @ CLACO

Posted by Aaron Sisemore (Member # 145) on 03-08-2003, 05:06 PM:

I will concur with Mark.

Dump the H gates and spring for the SA set.

I have had 2 H's (one retired, the other changed to SA gates) that had a constant problem with polyester dust accumulating at the lower portions of the trap causing exactly the problems you are describing. The stuff will compact itself so tightly it literally has to be 'chipped out' with a screwdriver or similar object to clear the trap and restore the focus.

-Aaron

Posted by Steve Kraus (Member # 476) on 03-08-2003, 06:38 PM:

We actually kept a dry erase board like this at Midwest Theatre Supply. Unfortunately I've forgotten most of the entries on it but there were several.

Posted by Mark Gulbrandsen (Member # 72) on 03-08-2003, 10:13 PM:

"We actually kept a dry erase board like this at Midwest Theatre Supply. Unfortunately I've forgotten most of the entries on it but there were several."
_____________________________________________________________

Yea, that board did change on occasion. I think there was a total of three or 4 machines on it over time.....DP-70, JJ, Simplex, and Century. Since we remanufactured so many Cast Iron Centurys(just over 100) I'll let that one stand. Just cutting off the front to install the Kelmar Turrett was almost impossible on those castings, and we eventually resorted to having them flame cut!

Mark @ CLACO

Posted by Fred Georges (Member # 505) on 03-16-2003, 02:22 PM:

A follow up. My poblem was operator error plain & simple. I found out that the projectionist changed formats (1:85 to 1:37) and failed to seat the lens collar correctly. The century H uses locator pins on the lens collar for focus. As he changed lenses He "thought" this pin just had to rest against the sleeve (not in the slot) Well He tried to Focus and took the rack to the end of it's travel which was just enough to put it in relative focus at the start of the show and that was it! While I agree the "SA" gate & trap is the way to go (It's Hell to clean the "H"s trap). This machine will be used once a month at best and the gate & trap are "FilmGuarded" between shows (No polyester crud sticks)The Art center will hold off on any change for now. The operator was familiar with Simplexes & SA's but, I guess, common sense was in short supply that afternoon. [Roll Eyes]