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This topic comprises 2 pages: 1 2
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Author
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Topic: Focus/anamorphic test films?
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 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
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 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
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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.
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