Film-Tech Forum ARCHIVE: Focus/anamorphic test films?

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Posted by John Hawkinson (Member # 1135) on 05-04-2008, 07:41 PM:

Tonight I needed to reset the throw on one of our anamorphic lenses in a hurry, and I wasn't really sure what the best test film to use was.

I started off with 35-AT (Cinemascope Projector Alignment), but the lines were not very fine at all, and I didn't feel that I could guarantee the focus was as sharp as I would like it to be. I switched to 35-FA (Focus & Alignment--Visual Test), which has a decent grid, but I still was not all that satisfied. Then I switched to some 35-IQ, hoping the resolution targets would be good, but they were really not convenient for doing this.

Is there a good test film that's recommended for anamorphic astigmatism adjustments? Ideally something with a lot of vertical and horizontal lines at varying spacings, i.e. very large resolution test targets?

(If I'd had a spotting scope, or a pair of binoculars handy, then perhaps the 35-IQ targets would have been good enough).

Looking at the sample image of CLT-2000, it doesn't look like it's really what I want either, but it may well be better than any of the other choices.

Thanks.

--jhawk

Posted by Brad Miller (Member # 2) on 05-04-2008, 07:42 PM:

Yes, it is called 35-PA, or more commonly known as RP40.

Don't forget your binoculars. They are a must to do the job properly.

Posted by John Hawkinson (Member # 1135) on 05-04-2008, 08:03 PM:

35IQ is the color version of RP40 (it has the same pattern as 35PA).

Squares aren't as nice to focus on as lines.

--jhawk

Posted by Brad Miller (Member # 2) on 05-04-2008, 08:16 PM:

I prefer to use the regular PA35 for this, as I find it makes precise focusing easier as I also look for color fringing to get everything dead perfect. With binoculars, you will be looking at the small squares of horizontal lines in each corner to set initial projector focus and then the small squares of vertical lines to set your astigmatism. You don't actually set the focus on the checkerboard squares.

Posted by Steve Guttag (Member # 268) on 05-04-2008, 10:50 PM:

I too use 35PA for this though the Schneider film will work too. I have not found the need for binocs to set astigmatism as there is a sweet spot where it really comes in.

If you defocus the anamoph to either extreme and then focus the image to bring the HORIZONTAL lines into crisp focus, you can then bring the anamorph into critical focus pretty easily (start by concentrating on the diamond in the middle. Once you convince yourself that it has perfectly focused cross-hairs, then go on to check the remaining targets (resolution) and verify uniform focus and that you can't make them any better (without making more worse).

Generally, with decent lenses that have low chromatic abberations, color fringing around the sqaures in 35-PA indicates less than optimum lamphouse/lamp alignment with the lens.

Steve

Posted by Brad Miller (Member # 2) on 05-04-2008, 10:52 PM:

But with binoculars you can tweek things to perfection. [Smile]

Plus if you have a turret and gate like the Christie projector has, you can really dial in perfect focus in all corners with the binoculars.

Posted by Frank Angel (Member # 248) on 05-05-2008, 08:47 AM:

In our large house (130 feet from the screen) binoculars are a must. The Simplex XLs have the focusing monocular mounted on the front of the projector but the optics in them are very poor contrast compaired to what you can get today with even inexpensive binoculars. I fancied that if I looked around, I might be able to get replacement lens elements maybe from a place like Edmund Scientific, but never really persued it due to time. I've left them on the projectors just cause they look so cool.

They are not really any good for anamorphic alignment because they are fixed to the body of the projector and cac see only one spot on the screen; you can't move them to see anyplace else.

Posted by Louis Bornwasser (Member # 3063) on 05-05-2008, 09:58 AM:

All of these thoughts are correct.

However, remember to focus the prime les first with no anamorphic attached. Then add the anamorphic. If you are focusing two lenses at a time, you are chasing your tail! Louis

Posted by Brad Miller (Member # 2) on 05-05-2008, 07:02 PM:

OMG, did Louis just say something incorrect???

Maybe Louis has a special procedure here. I can't imagine him being wrong since I don't think I have ever seen a post from him that was not accurate, but Louis...how exactly are you supposed to focus the prime lens, then remove it from the lens collar or turret to attach the anamorphic and miraculously maintain focus of the prime lens once you have reassembled and remounted everything?

Blurring the hell out of the astigmatism adjustment, using the projector's focus to get the horizontal lines into perfect focus and then without touching the projector's focus using the astigmatism adjustment to bring the vertical lines into focus is the proper procedure.

Posted by Jeremy Weigel (Member # 4208) on 05-05-2008, 08:29 PM:

I was thinking the same thing. I've not ever heard of this.

Posted by David Zylstra (Member # 4230) on 05-05-2008, 08:38 PM:

I've done it - tricky part is ending up with a picture square on the screen after the anamorphic is attached (I was never taught the procedure detailed on this site).

Louis could also be talking about some of the old lens changers where the turret switched between a magnifier and anamorphic - the prime lens was always in place.

Posted by Louis Bornwasser (Member # 3063) on 05-05-2008, 08:51 PM:

You focus the prime lens alone and leave it in place. Then carefully screw on the anamorp until almost tight; then focus the anamorp as described by others above. Lock astig ring tightly.

Finally disassemble, tighten and refocus the entire lens as a unit.

Again, you cannot focus the prime lens and the anamorphic correction at the same time. This is a divergent operation; best to focus only one at a time un til the anamorphic correction is finalized. Louis

Posted by John Hawkinson (Member # 1135) on 05-05-2008, 09:21 PM:

Well, Louis, Schneider's instructions disagree. (They also disagree with Brad). They recommend roughly setting the anamorphic, then setting the prime, then fine-tuning the anamorphic, and if necessary repeating the process.

I don't see why it should be the case that it should matter much; Whatever is easier for the user...

Schneider's catalog (pdf)

p.19, for their ES-Cinelux integrated anamorphic:

quote:

1. The projection distance is roughly set on the side scale by turning the FOCUS hexagon socket head screw with the supplied Allen wrench.
2. While the test film CLT is running, the projection image for the horizontal structures (lines) is focused using the standard focusing device of the lens holder or of the lens revolver of the projector. The marginal zone of the projection image must also be considered.
3. If the vertical structures (lines) are not yet fully in focus, the Allen wrench should be used to adjust the FOCUS screw for
fine focusing. If the horizontal structures go out of focus while doing this, steps 2 and 3 should be repeated.

p. 21 for their anamorphic attachments (including the reverse anamorphic, so the instructions are a bit weird):

quote:

Focusing the attachment
Unlike a normal lens, an anamorphic lens is not rotationally symmetrical: The WACinelux Anamorphic 2x leaves the vertical projection angle unchanged and stretches the horizontal angle considerably, as if the focal length of the base lens had been
halved, so that the image width is double.
In contrast, the Tele-Cinelux Anamorphic leaves the horizontal projection angle unchanged and narrows the vertical angle, as
if the focal length of the base lens had been doubled, which halves the projection image height. You therefore have to focus
and lock the focus as follows:
1. Loosen locking screw of the ring.
2. Use the knurled adjustment ring of the anamorphic lens to roughly set the projection distance on the side scale.
3. The lens is focused using the focusing
device of the projector: to the horizontal image structures with the WA-Cinelux and to the vertical structures (e.g. lines of
the test film) with the Tele-Cinelux.
4. Use the adjustment ring of the anamorphic lens to set the focus to the respectively other image structures. If the previously focused image structures go out of
focus, repeat steps 2 and 3.
5. Tighten locking screw.

--jhawk

Posted by Brad Miller (Member # 2) on 05-06-2008, 12:42 AM:

quote: Louis Bornwasser
Again, you cannot focus the prime lens and the anamorphic correction at the same time. This is a divergent operation; best to focus only one at a time until the anamorphic correction is finalized. Louis

Nobody is suggesting to try and adjust both at the same time. I am all for being even more anal on an alignment, so can you please tell me why is this obviously way more time consuming procedure better than the way I described? I cannot imagine how difficult it has got to be to deal with the anamorphic in this way...and what about integrated anamorphics?

By the way, nobody here has mentioned the importance of making sure the projector is absolutely level via the flat lens before even considering making an adjustment to the astigmatism on the scope lens. After all, if the projector is slightly unlevel, even if the anamorphic is rotated so that it appears to be level on screen...the astigmatism adjustment no matter how careful it is adjusted will not be precise and the focus will suffer.

Posted by Mark Gulbrandsen (Member # 72) on 05-06-2008, 02:10 AM:

I agree with Brad's method and its also the only way one can adjust boresight and convergence to perfection on a D-Cinema projector. The main thing is that you need to have very high quality binoculars and or a spotting scope... one that has minimum chromatic abberation when viewing through it.

Mark

Posted by Frank Angel (Member # 248) on 05-06-2008, 03:33 AM:

quote: Brad Miller
making sure the projector is absolutely level via the flat lens before even considering making an adjustment to the astigmatism on the scope lens.

How is the best way to achieve this? Is it good enough to just use the scope spherical lens or another longer focal length lens with a new and uncut 1.85 plate and assume the rectangle of the plate is true so then you can level the rectangle image you see on the screen either by a level or actually measuring the image placement. Or is there any place on the projector head that if you put a level you can get a reading that has enough "resolution" to get it perfect?

Posted by Brad Miller (Member # 2) on 05-06-2008, 10:46 AM:

You run PA35 through the flat lens and adjust it to your masking (the masking of which is easily verified with a level or tape measure). Since you are a changeover house, be prepared to intentionally skew the level due to keystoning, which at this point you have to eyeball it. Somewhere in the last few months I posted a lengthy set of instructions on how to setup and align a turret. I don't remember where it was though.

Posted by Sean McKinnon (Member # 612) on 05-06-2008, 11:53 AM:

AFAIK, And I could very possibly be wrong but I always thought that after you de-focused the scope attatchment and then brought the horizontal lines into focus that you were focusing the prime lens, then when you brought the vertical lines into focus with the attachment you were focusing the anamorphic?

Posted by Steve Guttag (Member # 268) on 05-06-2008, 11:59 PM:

Frank,

Ideally (and it is where I START)...you level the projector and then run a high precision target like 35PA (Schneider's test film will work too). If the lines are symmetrical on the screen and follow the masking, you are done. However, often you will find that is not the case. You then need to check the level of the drapes (masking) and if possible, get those fixed. If that is not immediately available, you will need to delevel the projector so the image is even and symmetrical on the screen.

People's only point of reference are those maskings so absolute level is less important than having the image look right. I'm not saying one should gloss over getting everything level...that IS the proper way. Your eyes will play tricks on you, especially on multiple projector installations. Often you are above the center line of the screen so your keystone will be skewed...that is, the lines at the top of the screen will seem much more in keeping with the top masking than the bottom of the screen. The opposite would be true if you are projecting up hill.

I use PC-Cine adapters almost exclusively to negate all of this in single lens machines. Many turrets will also allow one to shift the lens a bit (how much differs by manufacturer). Century offers lateral adjustment on their single lens machines and Simplexes may be adapted (or ordered) with the 35/70 upper lens guide to allow lateral lens shift.

What ever you do...do NOT use the aperture plate as your guide...there is no guarantee as to how that hole was cut and what reference it has. Some plates are machined and will have more precise holes...others are stamped and "you get what you get."

As to focusing anamorphics...Some Euro machines (Cinemeccanica comes to mind)...would put the anamorphic on a swing away attachment that would allow focusing as Louis describes. However, from his discription, Brad's and my techniques are pretty identical.

Note, in the current 35PA target, there are for oval/circles...they should all look like circles when the twist of the anamorphic is set correctly. If you have astigmatism problems in your eyes...you may have difficulty using them but they are a tell-tale sign of how well you got it. Schneider's target also uses a mixture of ovals and circles. Schneider also super-imposed a grid to indicate relative keystone.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 05-07-2008, 07:26 AM:

quote: Steve Guttag
Ideally (and it is where I START)...you level the projector

Hopefully not with any ole level... I highly reccomend the investment in a sensitive machinists level such as those made by Starret. These types of levels are the only ones sensitive enough to put any meaning to the term level.

Mark

Posted by Gordon McLeod (Member # 33) on 05-07-2008, 08:49 AM:

I level the machine using the flat lens against a line relative to the stage floor since that is what the audience sees as a level surface or the auditorium ceiling

Posted by Frank Angel (Member # 248) on 05-07-2008, 10:40 AM:

Gordon, funny you should say that -- just a couple of weeks ago we were in the process of rerigging our side masking track and legs and I was trying to get the legs to hang straight, i.e., at a perfect right angle to the top and bottom masking. I used a laser level, then used a water level. When the instruments said it was perfectly perpendicular, we'd go back in the orchestra amd eyeball it -- it looked slightly off. We'd set it to look good by eye, and the instruments would say it was off. I went back and forth like this, eye and instruments and finally I got fed up and asked four other guys to help decide and when we agree with what we all said looked perfect, I set it by that. I went back to measure, and the levels said we were off. Too bad. It has to look good, not instrument accurate. The only explanation we could come up with is that perhaps the geometry of the top and bottom curve of the screen (it has a slight perspective curve) and the curve of the proscenium had some affect on the perception.

Sometimes you just have to trust your senses.

Posted by Brad Miller (Member # 2) on 05-07-2008, 11:52 AM:

quote: Mark Gulbrandsen
I highly reccomend the investment in a sensitive machinists level

There is definitely quite a bit of confusion here. I am with Steve that being level with the screen is of most importance on an alignment. A physical level is simply not needed.