8mm Forum: ST1200HD Pressure Plate

This is topic ST1200HD Pressure Plate in forum 8mm Forum at 8mm Forum.

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Posted by Dan Lail (Member # 18) on December 17, 2003, 01:36 AM:

Hi, all, I have an ST1200HD with a focus problem. The ending of a reel of film tends to focus differently than the beginning and middle of the reel. Would this be the pressure plate springs not pressing the film flat at the end of a reel of film where the film is more curled? I don't have this problem on my ST800. Where can I get new springs?
Thanks for any info. [Confused]

Posted by Barry Johnson (Member # 84) on December 17, 2003, 04:13 AM:

A little known fact that affects all projectors of any gauge including 35mm/70mm is that during use,they actually expand!
This is attributable to the heat generated from the lamp source,and the heat energy created by the motors.
Even theatrically,focus has to be checked (or should be!) during the course of a film..............
If you wish to put the blame on to the print then yes,it has a small (very) effect due to how it forms when rewound/stored etc.

Posted by Dan Lail (Member # 18) on December 17, 2003, 01:04 PM:

Thanks, Barry, but I don't have this problem with the ST800. Also, this problem exist with any print I run on the ST1200. It's not a slight focus variation, but rather a substantial focus change. Anyone know where to purchase new springs.
Dan [Frown]

Posted by Kevin Faulkner (Member # 6) on December 17, 2003, 06:53 PM:

Hi Dan,
Now this is very difficult to explain to you but I have seen this on Elmos before and it can be caused by the "strip spring" which presses against the back of the lens. I think that with some older machines the focusing assy can become worn with use and then the focus knob becomes quite slack instead of stiff if that makes sense?
If you remove the lens and look down the lens holder you will see the "strip spring" I am talking about.
To check this out simply undo the cross head screw at the back of the lens holder which holds the spring in place. The spring is under the lens holders back plate, and then remove the spring. This will mean that you dont have the back pressure from the spring pushing against the rear of the lens. Focusing is less smooth but it might help your focus problem. If this isnt the case then you can put the spring back. Try not to undo all four screws on that back plate other wise the plate may go out of position. At least leave one undone.

Kev.

Posted by Dan Lail (Member # 18) on December 21, 2003, 06:32 PM:

Thanks, Kevin. I removed the spring and the focus from border to border improved, but I still have to tweek the focus about 85% of the way through a reel. I'm going to store a reel of film wound tails out for a while, then run it and see if that helps.

Merry Christmas to all across the pond. [Smile]

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[ December 21, 2003, 10:32 PM: Message edited by: Dan Lail ]

Posted by Kevin Faulkner (Member # 6) on December 22, 2003, 01:04 AM:

Definately worth a try then. Hope it helps.
Have a good Christmas from us across in the UK. [Smile]

Kev

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