Film-Tech Forum ARCHIVE: Focus problem with scope features only.

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Posted by Adam Budweg (Member # 1901) on 12-30-2004, 06:07 PM:

I work at an 8 plex where 1 house has a problem with scope features and the second i beleive to have teh same problem.
the lenses are
schneider scope lenses
on Vic 5's
with osram 2000w bulbs
at aprox 80 A

I first noticed the problem with the film the incredibles. The short bounding would require focusing and by the time the feature came about it had gone out of focus again. there is currently a print in there now and it isn't possible to aquire a crisp clear picture.

any advice would be much appreciated, keep in mind though I am in a bit over my head with this, I have no training in the lenses or the optics settings. I'm just stuck with this so they don't have to pay a tech $400 to walk in the door.

Thanks in advance for any help.
Adam Budweg

Posted by Mark Gulbrandsen (Member # 72) on 12-30-2004, 06:30 PM:

Start by checking the astigmatism adjustment(its not a focus adjustment!) on the anamorphic itself. You should have a length of RP-40 to do this properly. If you can't get it adjusted correctly then try swapping that lens to another screen and if the problem follows the lens then return it to Schneoder for repairs.

Mark @ CLACO

Posted by Steve Guttag (Member # 268) on 12-30-2004, 07:48 PM:

In addition to what Mark sez...budget in some ISCO anamorphics...they are the best, particularly the Blue-Stars.

Steve

Posted by Adam Budweg (Member # 1901) on 12-30-2004, 08:06 PM:

Thanks for the fast response. The astigmatism adjustment seemed to do the trick on the one, assuming the astigmatism adjustments are the numbers on the front quater of the lense. On a side note the numbers dont match up on all theaters, another one I checked was around 80, what does this setting do?

Regardless, I tried the same on the other house and could not turn that section of the lense. I removed the set screw completely and it would still not turn. Any suggestions?

Better lenses are out of the question [Frown]

(although i do believe we have a few isco flat lenses, or at least 2 boxes to isco lenses.)
we've been open for about 1 year and 1/2 and i still dont have a cleaner to use my film guard with.

Edit:
I checked the other lense after the show ended and I was able to adjust it. The lense was just tightened twards the infinity mark and I had to remove it to losen it up.
again thanks for the speedy help.

Posted by Brad Miller (Member # 2) on 12-30-2004, 10:49 PM:

1. Thread the loop of PA35 test film into the projector, making sure the loop does not hang in front of the lens. Depending on the particular anamorphic you are using, you may have a small thumbscrew, set screw, or a ring collar at the front of the lens. Loosen the locking mechanism so that you can freely turn the outer focusing (or more precisely: the astigmatism adjustment) ring (labeled with measurements, commonly from 20 feet to 150 feet). Note the current setting before changing it for reference.

2. Turn the focusing ring all the way down as low as you can go (about 20 feet). If you are in a short throw theater, such as a screening room, you might be better off turning it to it's infinite setting (typically 150 feet).

3. Turn the projector and lamp on. Notice the image will be incredibly blurry. Use the projector's focus control to focus the horizontal lines on screen to be as sharp as possible. Ignore all vertical lines. Once you get the projector's focus set in this manner, do NOT touch it again for the rest of this process.

4. CAREFULLY and slowly, turn the focusing ring on the anamorphic lens itself. Continue to turn it until the vertical lines converge and become as sharp as possible. Again, ignore all horizontal lines.

5. Now, without bumping the focus setting on the anamorphic, tighten the locking mechanism.

Your lens is now optimized for your projection throw. Because this method is accomplished by focusing through the lens as opposed to counting the distance from lens to screen (commonly by counting ceiling tiles), your end result will be a sharper image.

If you don't have an RP40/PA35 loop of film, you can use a scope green band from a trailer to get pretty close (but not *quite* as accurate as using a real test loop). Thread the green band loop 2 perfs out of frame and use that horizontal frame line to set your focus...then re-center the framing and adjust your astigmatism adjustment on the anamorphic until the letters in the text are as sharp as possible.

Posted by Randy Stankey (Member # 64) on 12-30-2004, 11:47 PM:

Although the astigmatism is one of the first things I would check as well, the fact that the lens goes out of focus during the show puzzles me.

That seems to suggest a problem in the lens or lens holder assembly.

Is the projector in focus when you first start it up? Or, do you have to focus it upon starting?

How long does it take to go out of focus? Does it happen gradually or suddenly?

Does it happen at the same point in the program or in some predictable way?

Has your adjustment of the astigmatism solved the problem completely?

Do you have all-in-one anamorphic lenses or two piece ones with a "normal" lens and an anamorphic attachment screwed on? If you have a two piece Scope lens, it's likely that the anamorphic attachment was loose. Your twisting the lens to adjust the anamorphic attachment might have tightened it again.

Hey, if your problem is solved then don't worry. Like I said, I just got puzzled.

(Puzzlement is often a normal state of mind for me, though! [Wink]

)

Posted by Jason Black (Member # 684) on 12-31-2004, 12:09 AM:

Sounds to me like a loose lens element in the primary, or anamorphic, side of the scope lens...

I should know. I've replaced about 7 of them now... I ask for ISCO only now. Haven't had one long enough to se if the Christie turret beats it all to hell and back or not... [Mad]

And yes, as others said, adjusting it for proper throw is a good thing to do as well but, generally speaking, if it's an issue of focal "drift" then it sounds like a loose element....

Posted by Adam Budweg (Member # 1901) on 12-31-2004, 09:16 AM:

Well we don't have any test film in stock but when i get a chance I'd like to try the technique with the trailers green band. As of right now I did the best I could with an adjustment durring the credits.

In regards to it going out of focus during the feature or gradually no, both houses stayed consistently unfocused. There would be a noticeable change between some trailers, but both the previous and the following trailer would be out of focus.

Yes, it did seem to fix the problem (thanks again)

They are 2 piece lenses, but it was firmly in place on both lenses.

In regards to christy turrets they do twist the lense from time to time. It's that or some one has the bad habbit of leaning on or messing with the scope lense when its set to flat. I have had to tightened the lense holder a few times in other houses.

Posted by Rich Ferrando (Member # 2056) on 12-31-2004, 12:44 PM:

We've had a similar problem on one of our projectors for some time. Specifically, the lens (all lenses, not just scope) will lose focus at each splice during trailers, but never during the feature. Generally speaking, running our Kelmar with Film Guard reduces the issue.

Last night I changed the bands on this particular projector (it's a Century SAW) to eliminate a steadiness issue, and the focus problem seems to have ceased after doing that, but I can't fathom WHY. It's seems highly illogical to me.

Posted by Dave Macaulay (Member # 813) on 12-31-2004, 01:42 PM:

The numbers on the scope attachment are supposed to mean the projection throw. With a properly assembled lens, setting the throw distance will give you a decent picture although you should do the correct setup as previously described.
The numbers may read completely wrong though. The front part that turns is screwed into the lens body with a multi-start thread. If someone removes the front by accident or by design, there is at least one wrong way to thread it back in - although the lens will work just fine the distance numbers will be meaningless and the only way to set the astigmatism is by using the test film.

Posted by Darren Briggs (Member # 1071) on 01-01-2005, 12:19 PM:

Had one stange problem once like this at one of my sites and it was down to the backing lens becoming loose from its lens barrel.
As the film ran it vibrated the lens slightly and the lens unscrewed a fraction and henc varied the focus.

Darren

Posted by System Notices (Member # 2357) on 07-18-2006, 08:25 AM:

It has been 562 days since the last post.

Posted by Iben Jimenez (Member # 3713) on 07-18-2006, 08:25 AM:

Well I have a couple of questions about the astigmatism adjustment. Is there an easy explanation to why you have to adjust the focus in the projector and the distance ring in two different steps? What is really astigmatism? What about the variable prime lens, is not the same thing?

Thanks

Posted by John Pytlak (Member # 331) on 07-18-2006, 08:56 AM:

Astigmatism is when a lens does not focus horizontal and vertical lines at the same point:

http://en.wikipedia.org/wiki/Astigmatism

quote:
In optics, astigmatism is when an optical system has different foci for rays that propagate in two perpendicular planes. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances.

http://www.vanwalree.com/optics/astigmatism.html

quote:
In the presence of astigmatism the rendering of an object detail depends on the orientation of that detail. For instance, a (short) line oriented towards the image center is called a sagittal (radial) detail, whereas a detail perpendicular to the radial direction is called a tangential detail. The astigmatic lens may be focussed to yield a sharp image of either the sagittal or the tangential detail, but not simultaneously.

Most "scope" lenses use cylindrical optical elements that must be adjusted for the distances (conjugates) used in a given projection situation. These lenses usually have an adjustable calibrated "distance ring" that can be set to the distance from projector to screen. But optimum adjustment should be made using a resolution target like the SMPTE 35-PA (RP40) test film, so that vertical and horizontal lines come into focus at the same point.

Posted by System Notices (Member # 2357) on 08-09-2007, 12:18 AM:

It has been 386 days since the last post.

Posted by Mike Frese (Member # 4361) on 08-09-2007, 12:18 AM:

I am also having the same problem. Focus is fine on flat, but problematic with scope especially with The Simpsons Movie.

I have tried the test that Brad recommended with the scope green band without much luck.

My equipment: Simplex XL, Kollmorgen lens with cinemascope attachment II from Bausch & Lomb.

Should the astigmatism adjustment ring keep going round and round endlessly or should it stop at some point? The adjustment of the ring seems to have no positive effect.

Thanks

Posted by Jeremy Weigel (Member # 4208) on 08-09-2007, 01:31 AM:

I'm not familiar with your brand of lenses, but can you see any change in focus when you adjust the ring?

Posted by Monte L Fullmer (Member # 2797) on 08-09-2007, 03:38 AM:

quote: Mike Frese
with CinemaScope Attachment II from Baush & Lomb.

Uh-oh, wonder if the glue that holding the elements inside the barrel is decaying (elements inside looking on the yellowish side, and the glue that holds the elements to the barrel-is that all yellowish as well), and has this lens suffered excessive heat due to someone leaving the lamp on without dowser being closed and cooking up the glass inside?.

The outer ring controlls the focus to the base lens with those footage marking on the outside corresponding to the throw from machine to screen. If that gets all wigged out of wack, one needs to know how to use screen alignment film to bring these attachments back for proper focus.

That's an old attachment you have there and B&L's are fewer to be found in service.

Also, you mentioned XL: is this the old black wrinkle cased model, or the NSS/grey cased model? For the trap and gate assembly:flat or curved? If flat gate, the runners in the gate is prob not holding the film flat and causing the slight focus shift during the scope presentations...along with a high wattage bulb...since you didn't mentioned what bulb wattage you are using.
good luck - Monte

Posted by Mark Gulbrandsen (Member # 72) on 08-09-2007, 08:10 AM:

That ring on a scope lens actually adjusts ASTIGMATISM... not focus. It is an entirely different effect than a focusable lens.

quote: Monte L Fullmer
Uh-oh, wonder if the glue that holding the elements inside the barrel is decaying (elements inside looking on the yellowish side

Actually the yellowish color you sometijmess ee in B&L scope lenses is caused from the addition of flourite in the glass mix. It takes alot to actually burn the balsam cement used in those lenses. I;ve only seen one or two over the years that were "cooked". ON the other hand I've also seen some exceptional B&L scope attachments the equal or exceed the image quality of Schneider and ISCO attachments. Those are also few and far between. There are still many B&L's in use on my service routes.

Mark