Film-Tech Forum ARCHIVE: Drifting Focus

This is topic Drifting Focus in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Patrick Matthews (Member # 2705) on 10-17-2005, 02:59 PM:

Hi all, out projector (PRO 35) has been drifting focus recently. It is just the second projector (we have two for changeovers) and I just can't seem to get the whole picture in focus. This happens on scope and flat film. There is nothing on any of the runners or in the gate that is obstructing the film and I just can figure it out. Any ideas?

Posted by Jeff Taylor (Member # 443) on 10-17-2005, 03:06 PM:

Is the whole picture drifting out or in and out of focus uniformly, or are you having problems pulling an even focus i.e. center to edges or left to right?

Posted by Patrick Matthews (Member # 2705) on 10-17-2005, 03:13 PM:

I'm having trouble getting a uniform focus. Either the center of the screen will be in focus but not the edges or visa versa.

Posted by Monte L Fullmer (Member # 2797) on 10-17-2005, 04:22 PM:

Check both lenses to see if the elements inside are loose. Age can cause the lock rings to come unscrewed abit to make the elements not be tight within the element barrel.

Tap the barrel and see if the elements rattle within. Elements loose will have problems of maintaining proper focus.

You also could have some burnt lenses. Anyone left the dowser open and left the lamp on (which is lethal to lenses with naked light cooking up things inside)?

With scope, wonder if the fine focusing ring has been altered some to cause improper focus with the anamorphic attachment(s).

-Monte

Posted by Marin Zorica (Member # 1716) on 10-17-2005, 04:31 PM:

Also you must check you film gate!

May bee tension is too high and film runs squized so distance from every part of film in frame to lenses is not same.

Or film gate isn't positioned in parallel with lens holder,and then off course with lenses.

Posted by Scott Norwood (Member # 30) on 10-17-2005, 05:30 PM:

What kind of gate does the Pro35 have? Is it like a modern Simplex/Century SA gate (curved with tension bands), an older-style Simplex/Century C or H gate (straight or curved, but without bands, and with two tension adjustment knobs), or something totally different?

What size lamp and what type of lenses (focal length and f/stop)?

What happens if you interchange the gates and traps between machines (if that's even possible; I'm not familiar with the Pro35)?

Posted by Patrick Matthews (Member # 2705) on 10-17-2005, 05:52 PM:

It is the older style with straight and the two tension knobs. We have a 2k lamp and our throw is 48 feet.

Posted by Dan Lyons (Member # 1454) on 10-17-2005, 06:00 PM:

turret or single lens model?

Posted by Patrick Matthews (Member # 2705) on 10-17-2005, 06:11 PM:

Single Lens

Posted by Monte L Fullmer (Member # 2797) on 10-17-2005, 06:50 PM:

PRO35 units from Ballantyne are one of the most unique, yet aggravating machines ever built. The plus being that the whole transmission is fully encased in an submerged oil bath with an oil fill on the outside of the case with an oil level marking.

Then, the other end of the belt pulley shaft is the cam for the intermittent (and a pretty good sized intermittent assembly as well)And ... there's that damned coupling device to frame with since the intermittent assembly doesn't roll on its axis as does the Simplex, or move up and down as with the Century and Christie.

But the intermittent shaft is split in two-one end with the starwheel and the other end holding the sprocket, with spiral grooving at each end of each shaft with a nylon coupler that slides back and forth between the spirals to "rotate" the intermittent sprocket for framing....) This was made so that the shutter didn't have to compensate for the attack (first sprocket hole) position of the intermittent sprocket. Dowser is a central hinged plate on the shutter shaft with a goofy type of spring selinoid to pull that thick plate of aluminum up.

PRO35's looked like it borrowed some parts from the Simplex, mainly pad roller assemblies, gate and trap parts (all flate gate variety) and shoes of sorts.

PRO's were mainly single lens models, with the exception of the MARK-VII that had the sliding lens bracket to hold both lenses-and the flat lens was a Magnacom lens since both lenses used one common base lens mounted in the lens frame.

If you know how to thread a PRO just right, they can be a very quiet machine. But if the loop sizes are a bit too small, or a bit too big, then these PROS can sound like thrashing machines beating themselves to death.

"Mr.Scott", if you want to "bone" up on a PRO-35, head to the manual section, open up the PDF on a PRO-35 manual and do some studying on these beasts. Here is some very good reading in store for you.

-Monte

Posted by Darryl Spicer (Member # 711) on 10-17-2005, 07:56 PM:

check the latteral guide on the gate trap for dirt accumulation around the spring and against the guide. There should be movment in the guide. Just remove the screw and the square guide and clean it off and rotate it from what it was because there probably is a groove in it too. Make sure to clean out around the area the guide goes in.

I used to run pro 35's for about 8 years. Other than keystoning and or lens issues I have found the guide to cause focus issues as described if it does not move out enough to allow the film not to bow in the gate.

Posted by John McConnel (Member # 2000) on 10-17-2005, 08:02 PM:

Have you exchanged lenses between projectors, to confirm that it's not a lens problem?

Posted by Louis Bornwasser (Member # 3063) on 10-17-2005, 08:08 PM:

Interestingly, the pro-35 is an Americanized FP-35. (Ballantyne was once the Norelco (Kinoton) distributor for North America......until they copied the machine.) Louis

Posted by Gordon McLeod (Member # 33) on 10-17-2005, 08:26 PM:

Actually they were assembling the FP20 (building the lamphouse table and column) as well as casting some of the bases for the DP70

In this case I suspect that the rails are causing the film to cup away from the lens (also a lamp that has a hot spot will make it worse)
There is a spring loaded presure pad at the top of the trap that could be the culprit also the rails can be moved in and out and they may have shifted (an alignment tool is required)
Also even though the gate lookes straight some of them had a radial curve