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Topic: boresight adjustment

Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 04-30-2013 08:46 AM

Is there anything to watch out for when doing this on a Christie CP2220?

I am familiar with large-format photography and have read the projector manual and understand that the basic concept is to tilt the lens with respect to the "film" (chip) plane in order to achieve edge-to-edge/corner-to-corner focus across the entire frame.

Is there any reason not to adjust this in a theatre where the video projector has significant vertical and horizontal keystoning issues? The D-cinema installation in this place is of somewhat questionable quality (they are using the factory color presets, among other issues) and the boresight adjustment was evidently not done at the time of installation. At the moment, it is impossible to get even focus across the entire screen. Curiously, the 35mm projectors are equally offset from the screen centerline and do not have any focus issues at all (the D-cinema projector got the third porthole off to one side).

Is there any interaction between the boresight alignment and the convergence? From what I can tell, the convergence adjustment is probably not something that should be touched by the operator.

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Gavin Lewarne
Master Film Handler

Posts: 278
From: Plymouth, UK
Registered: Aug 2009

posted 04-30-2013 09:56 AM

We have a somewhat mild keystoning issue at our place that cannot be helped, and our boresight / scheimpflug has been able to achieve razor focus in all corners and centre.

Picture quality is great and now that the lens has been running format changes for several months everything seems to have settled and the lens doesn't need re-adjustment every couple of weeks (it did when new)

I still run test patterns every week though to check lens alignment, focus and zoom just to be sure.

As for convergence when the scheimpflug was initially adjusted on install (tech said it was a pretty big adjustment) and once more by me several weeks after (tiny tweak) it did not seem to make any appreciable difference to convergence according to the various test patterns

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 04-30-2013 01:28 PM

Don't worry about convergence for your issue. The boresight is your key to even focus in all 4 corners. Just make sure you have a telescope on a tripod or a steady hand with binoculars. Don't try to do it with your eyes alone.

USL also makes a cool camera for this, although I've yet to try it, other techs I've spoken with have praised it.

I've achieved perfect boresight on some crazy-off-center installs. Keep in mind that won't fix your keystoning though. The projector should be as squared off to the screen as possible (no tilt) and the adjustment made with the lens controls. Only if you run out of offset in the lens should you start tilting the projector or twisting the projector to get the image on the screen. Also remember to never expect to "save" a lens setting at the extreme of it's range. So if you have to add a little tilt to the projector, add a little bit more tilt than you need and back off of the extreme of the lens adjustment.

Since you used the term boresight, I'm assuming this is on a Christie. You should be able to get amazingly accurate control with minimal effort.

If you are doing this on a Barco C, don't be surprised if you don't have to keep adjusting the boresight (scheimflug) just to get a happy spot in between actually being in focus on screen vs. hitting the prism. There is VERY LITTLE ROOM in a Barco C for adjustment! Also on Barco B models, make sure you don't go crazy with the adjustment, as you can EASILY bend the lens mount, which will require changing of the mount to correct the damage.

You will also find that you may have boresight perfect in one format, but when you switch to another, the boresight is no longer spot on. I attribute this to their non-Minolta lenses, as I've not seen the issue on Barcos with Minolta lenses.

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