Film-Tech Forum ARCHIVE: Focusing scope lenses issues

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Posted by Frank Dubrois (Member # 3042) on 12-15-2005, 01:39 PM:

I seem to have a problem regarding focusing scope movies. I use the correct film loop (rp35?) to focus our lens' to pinpoint sharpness. After removing the focus film loop, i'll thread up a movie and play it. Immediately it is VERY out of focus. All the previews, policies and the movie itself is VERY out of focus.

If the loop that we use to correctly adjust focus shows perfect focus, why are the movies so out of focus? This happens repeatedly and is not a one time oddity. Anyone know what the deal is? Are we doing something wrong here? Thanks.

Posted by Ken Lackner (Member # 1002) on 12-15-2005, 01:44 PM:

Someone will correct me if I am wrong, but I believe RP-40 is printed on black-and-white film stock, and therefore the focus will differ from the trailers and features. It's best to focus during the credits of the feature you are trying to focus. You could make a loop out of a green band from a trailer and use that, but even that may differ slightly from the feature due to differences in film stocks used.

Posted by Christos Mitsakis (Member # 143) on 12-15-2005, 02:04 PM:

Frank,
you must use longer film length than a loop. The problem is the cumulative heat that the loop absorbs. The film curls and you are trying to correct that drift by focusing. That's why when you thread and play a normal reel you are always out of focus both in scope and flat.

Christos.

Posted by Scott Norwood (Member # 30) on 12-15-2005, 02:12 PM:

Also, RP-40 is a camera original element, and the emulsion will be on the lens side (versus lamp side for an ordinary release print). It isn't really intended for focus adjustment, but rather for aligning the image on the screen, setting masking stops, and cutting plates.

I've seen RP-40 (err...35PA) printed on both B&W and color print stock; maybe someone else can explain the difference.

Posted by Frank Dubrois (Member # 3042) on 12-15-2005, 04:47 PM:

quote: Ken Lackner
focus during the credits of the feature

Are you talking about opening credits I hope? I've been told that focusing to the end credits is a real bad idea. I thought that you were supposed to focus to the eyes somewhere in the middle of the screen.

quote: Christos Mitsakis
you must use longer film length than a loop. The problem is the cumulative heat that the loop absorbs.

I considered the heat issue, and as soon as I turned the projector on, I made a quick focus adjustment and then started the feature, the same thing happened.

Posted by Ken Lackner (Member # 1002) on 12-15-2005, 07:32 PM:

When I made my comment I had the end credits in mind, but anythng with titles should be fine. Why do you say it is a bad idea to focus during the end credits?

Posted by Mark Gulbrandsen (Member # 72) on 12-15-2005, 07:45 PM:

Guys, Don't forget that when you "focus" the scope lens itself(not the projector focus) you are actually adjusting it for minimum astigmatism.....

Posted by Richard May (Member # 2627) on 12-15-2005, 08:59 PM:

Bad idea focusing on end credits. I have found them many times not to be in great focus.

Posted by Frank Dubrois (Member # 3042) on 12-16-2005, 12:01 AM:

Yes, focusing to end credits very bad. Same as focusing to policy trailers or movie trailers. Unless its REALLY out of focus, the best way to focus I guess is during the movie. Focus to the eyes, dead center.

Posted by Peter Mork (Member # 1336) on 12-16-2005, 12:07 AM:

quote: Ken Lackner
Why do you say it is a bad idea to focus during the end credits?

Here's the word from my man Woody (don't call him The Woodman - he hates that).

(Personally I never noticed a problem with using end credits to focus - except of course the movie's already over - but I'll grant that different projector/lamp setups can vary a lot.)

I wish more filmmakers would care enough to write us down here at the bottom of the food chain.

Posted by Brad Miller (Member # 2) on 12-16-2005, 03:48 AM:

It seems to depend on projector make as well as the amount of heat in the gate more than anything. For example, some theaters I have worked at the end credits would always be out of focus because of the heat. Others it was a great way to tweek the focus for the next show.

So far the projector that will just run anything with perfect focus is the Kinoton. I recently ran a collection of old snipes through one and not once was the focus anything less than perfect. Bear in mind this was with various film thicknesses (polyester, acetate, IB, etc) and some of the snipes were so horribly warped it was amazing they made it through the projector. Running that reel on any other projector required constant tweeking of the focus. On the Kinoton, you can run anything and NEVER touch the focus. [thumbsup]

Posted by Monte L Fullmer (Member # 2797) on 12-16-2005, 03:53 AM:

quote: Scott Norwood
It isn't really intended for focus adjustment, but rather for aligning the image on the screen, setting masking stops, and cutting plates.

..but if you run emulsion lens side, your wording onthe 35PA loop will be upside down. I've always emulsion out as with the film since we need to do the stuff that you mentioned as if we are working with the actual film.

But, it's good stuff when you target in an anamorphic element to focus in the base lens (horizontal lines) then focus in the throw length (vertical lines). Plus, it's good stuff to where you can center in a turret that has all of the "X","Y", and "Z" adjustments (using flat lens with no aperture plate), which is done after centering the machine to the screen.

Then you dive into the centering of the anamorphics-which could correct a bunch of focusing problems being that possibly and probably most projector's anamorphic attachments, single lens and turret models, are horribly mounted off-center to the film plane to screen out there and the common operator doesn't even know anything about this.

Course, another big thing that was mentioned to me by Steve G., that with turret lens operations, especially the manual ones that sudden rotational movement of the anamorphic lens can actually shift the glass elements inside the attachment, causing focusing problems to where these attachments has to be sent into the shop for disassembling to refocus the mulitude of elements inside that attachment. I know of about 4 attachments that needs to be sent in for refocusing since a sharp focus with these attachments is vacant.

So, take it easy when swinging that turret around in that turret frame-there's quite a bit of weight and a lot of glass hanging in front there, especially if you have the older attachments. And if your popping in lenses for you single lens users out there, don't jar, slam and shake around those big lenses either when shoving that lens into the lens holder assembly of the machine.

-thx Monte

Posted by John Pytlak (Member # 331) on 12-16-2005, 08:30 AM:

quote: Scott Norwood
Also, RP-40 is a camera original element, and the emulsion will be on the lens side (versus lamp side for an ordinary release print). It isn't really intended for focus adjustment, but rather for aligning the image on the screen, setting masking stops, and cutting plates.

I've seen RP-40 (err...35PA) printed on both B&W and color print stock; maybe someone else can explain the difference.

No, SMPTE Recommended Practice RP40-2003 specifies the following:

quote:
5 Film types and exposure
The test film described in this practice shall be photographed using a style B camera aperture as specified in
SMPTE 59. Because of the need for extreme steadiness in the test film, it is recommended that these test films
be manufactured as camera originals using pin-registered cameras. When manufactured as camera originals,
the image shall be photographed so as to project correctly in the usual print emulsion position (emulsion toward
light source). If the test films are to be manufactured as prints, the printing method must be capable of
maintaining the resolution of the original image and shall not introduce any unsteadiness in the images.

It goes on to say:

quote:
The test film described in this practice shall be produced on 35-mm motion-picture film manufactured in
accordance with ANSI/SMPTE 93. A perforation pitch of 0.1866 in (4.74 mm) or 0.1870 in (4.75 mm) is acceptable.
The test film described in this practice shall be produced on a black-and-white silver-image film capable of at
least 80% modulation transfer at 80 line pairs per millimeter. It may also be produced on a color positive film
in which the exposure has been limited to the top (magenta) layer only to provide maximum sharpness

The silver image film is sold as 35-PA. The color version is sold as 35-IQ. The silver image film (35-PA) is more sensitive to heat issues from absorbed infrared energy, and so is more useful to diagnose those issues. The color version will focus at a point more like color prints, since it absorbs less infrared energy.

Posted by Frank Angel (Member # 248) on 12-17-2005, 07:14 AM:

It is very upsetting to get to the final credits and find out you are out of focus!

Some theatre configurations -- short throws with big screens are more susceptible to focus problems that others because that combination reduces the depth-of-field to a point that it is intolerant of almost any variation in film position due to heat absorption. In our 2500 seat house, the DOF is so good that I can rack the focus back and forth slightly without any focus change. The down side is, I have to use binoculars since the booth is so far away from the screen, but once I'm is in focus, [i]I'm in FOCUS! And then good projectionists should check film focus from time to time throughout the presentation anyway.

What really surprised me about the Woody Allen "can" note, is that he assumes some presentations will be so poorly focused that by the end of the film, it will be so far out that people wouldn't be able to read the credit crawl. I would think he would have been be more upset that everything before the credits was that far out of focus! [uhoh]

Posted by Larry Myers (Member # 738) on 12-17-2005, 10:52 AM:

I am building a small home theater with booth in a bonus room above the garage. The scope screen size is 3.5 by 8 ft and the projection distance is 12 ft. The view distance is 9 ft. I am using a factory rebuilt Devry 12000 HD. After trying many different lens combos, I find that a 60mm ISCO Ultra Star HD with a Super Cinelux compact anamorphic works best for me. Although, it took me forever to get that anamorphic lens in true focus. I finally had to post a resolution target on the screen and use a 40x loupe at the back of the lens to get the anamorphic fully in focus.

The interesting thing about the anamorphic focus range is that the lens seemed to correct for Astigmatism from the tick marked 15 ft to 9 ft range but only one point in the focus range gave the best image contrast. This point on the lens tick mark said 10 ft but the film to screen distance is exactly 12 ft.

To me, the image quality now is just outstanding. More so if I am running something shot in Panavision and Kodak Vision Stock.

Posted by John Hawkinson (Member # 1135) on 12-17-2005, 09:39 PM:

Frank, I think you misunderstood Woody Allen. I believe he is saying that because white credits on a black background absorb a lot more heat than the rest of the film, they are much more likely to be subject to embossing, and thus to have a different focus point than the rest of the film.

--jhawk

Posted by John Pytlak (Member # 331) on 12-19-2005, 10:14 AM:

I recall a recent B&W production with silver-image prints had intertitles that alternated between white letters on a black background, and black letters on a clear background --- the focus difference due to varying levels of curl from the radiant energy absorption was quite noticeable, especially on larger screens with large lamps and short throws (less depth of focus).

Despite numerous Kodak publications, people sometimes forget how much more radiant energy silver-image B&W prints absorb.

Posted by System Notices (Member # 2357) on 01-23-2009, 06:00 AM:

It has been 1130 days since the last post.

Posted by Justin Hamaker (Member # 2165) on 01-23-2009, 06:00 AM:

Not sure if this is the correct thread to post this or not, but I've always had issues getting a sharp focus in scope on one of my houses. Tonight when I was playing around with it, I realized the scope lens comes apart into two pieces, one of which looks like our flat lenses.

I also realized there was a ~1" ring that appears to have been removed from the lens - it's been laying around since I came to this theatre and I never knew what it was for. Just for grins, I put this piece between the two other pieces.

When I put the reassembled lens in place and ran a test loop, I was able to get it focused better than I could ever remember. Does this sound correct?

For what it's worth, it's a Schnieder(?sp) lens.

Posted by Jonathan Althaus (Member # 5042) on 01-24-2009, 12:27 AM:

Sounds like the throw adjustment. We had one Schneider scope lens never focus, turned out someone had adjusted the throw, and that was the whole cause.

Posted by Monte L Fullmer (Member # 2797) on 01-24-2009, 01:03 AM:

.

That 1" ring mentioned is for your focal length between the "prime lens" (what you mentioned as the 'flat' lens), and the attachment that is set for your location there. With you adding it, it lengthened the distance from the prime to the attachment so the attachment adjustments could be made better.

You oughta see scope lenses for drive-ins: a pretty long lens due to the length of spacing inbetween the prime and the attachment since they got a super long focal length.

By lengthing the distance, it keeps the light within the glass elements inside the attachment itself instead of flooding against the side of the attachment barrel when leaving the front lens - prob why you were having focus issues.

Kinda image an "X" with the middle of the "X" being the back of the lens. the right legs of the "X" has to pass through the lens without touching the inner walls of the entire lens barrel - why of these spacers..