Film-Tech Forum ARCHIVE: Sharpness Degradation

This is topic Sharpness Degradation in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Muhamad Taufiq (Member # 8868) on 12-28-2017, 06:37 AM:

When a projector is newly installed, it tends to produce nice and sharp images. But as time goes on, the image starts to lose its sharpness. So I'm curious what is the usual cause for something like this?

Posted by Carsten Kurz (Member # 5396) on 12-28-2017, 07:06 AM:

One potential reason is dirt collection in various areas of the projector. One should have a trained tech on site every one or two years for a full cleaning.

The other issue may be focus drift that occurs more or less often with some machines. Lens presets should be checked every few months and corrected/redone if necessary.

- Carsten

Posted by Muhamad Taufiq (Member # 8868) on 12-28-2017, 08:28 AM:

Only because of dust or focus then? Is there something that has to be regularly replaced, but if failing to do that would result in loss of sharpness?

Regarding dust I would assume it's only necessary to clean from lens up to prism, since integrator rod etc is before the chip, so if there's dust in there it would only affect brightness and not sharpness. Is this correct?

Sorry if this is all seems like a stupid question, I'm just really eager to learn more about (cinema) projector.

Posted by Jim Cassedy (Member # 4115) on 12-28-2017, 09:49 AM:

While, as Carsten says, internal dust can be a factor, my personal
experience with the machines I work with is simply "drift" from due
to the limited mechanical tolerances of the focus mechanism gears
& servos. Those systems are pretty good, but in reality each time
a format/focus change is done, the lens gears don't wind up 100%
exactly where they should be. The error is very small, but over a
period of time those tiny position errors add up to enough to the
point where it starts becoming noticeable on screen as soft focus.

I work with several NEC projectors, and I've found that with the
usage pattern they get, I have to check and touch-up the lens
macros about every 2-3 months. Even if they "look ok" on screen,
I've noticed they benefit from a bit of adjusting, which becomes
most obvious if you've got a good focus/resolution chart to use.

. . and as Carsten says, an occasional professional projector
cleaning will also help insure you're getting clean & clear images.

Posted by Leo Enticknap (Member # 534) on 12-28-2017, 05:35 PM:

99% of my operating and servicing experience on digital projectors is with Barco and NEC, and I would agree with Jim that NECs are worse for focus drift.

However, for any make of digital projector, I would recommend that monthly (if the theater has someone on site who is capable of doing this), or at every planned maintenance call if not, the following is done:

- Remove the lens from the projector, clean the glass element at both ends, and lubricate the gears of the focusing mechanism, then reinstall.

- Perform home and return (Barco)

- Hook a wifi access point to the management network (if you don't have permanent wifi access installed), then go down into the house with your laptop, stand right next to the screen (as in, 2-3 feet from it), then for each lens file, project a test pattern, adjust the focus until you can see the individual pixels, then save it.

Check for focus uniformity (Scheimpflug), too, though obviously, this can't be adjusted remotely. A pair of binoculars comes in very handy for this.

Posted by Buck Wilson (Member # 5885) on 12-28-2017, 07:42 PM:

Also convergence is a thing that can cause blurry looking soft images.

Posted by Stephan Shelley (Member # 8587) on 12-28-2017, 08:23 PM:

Christie's lens settings drift as well though more lens shift than focus.

You did not say what brand of projector. Sony's the device that produces the image degrades with age and causes image issues.

Posted by Muhamad Taufiq (Member # 8868) on 12-28-2017, 09:06 PM:

Most of these issues are in Barco projector, particularly C and S series. I almost never seen this issue on a site with B series and Christie (I assume if they can afford these projector, they can also do proper maintenance).

Posted by Leo Enticknap (Member # 534) on 12-29-2017, 10:09 AM:

In my admittedly very limited time as a service tech, I've never come across a projector in which the convergence has drifted, unless it's just been shipped (in other words, a new installation), or the light engine has been pulled and reseated (or replaced). Even then, not always. I replaced a light engine in a DP2K-32B last month. The "new" light engine was actually a used one we had in stock, that had been pulled from a projector that had been totaled and parted out for an unrelated reason (water damage, if I remember correctly). After the light engine swap was done, the back focus and focus uniformity both had to be reset, but the convergence was perfect: all the pixels looked perfectly aligned, even standing right next to the screen.

One thing they didn't teach me in Barco school is that the adjustments that need you to touch the projector to do - back focus, focus uniformity and convergence - are a darn sight easier when the projector is projecting onto a whiteboard 15 feet away in a classroom, than a screen 50 feet away in a theater. A telescope or a pair of binoculars (doesn't need to be fancy or expensive) is an essential toolkit item for any job that could require adjustments to the optical system.

Posted by Mark Gulbrandsen (Member # 72) on 12-29-2017, 11:31 AM:

quote: Leo Enticknap
I would agree with Jim that NECs are worse for focus drift.

It seems to be highly dependent on which lens is in the projector as I have many sites that never drift and other sites that I actually touch up by remote fairly regularly. It would be interesting to make a chart of which lenses get re-set the most.

Mark

Posted by Leo Enticknap (Member # 534) on 12-29-2017, 12:07 PM:

How to you touch up by remote? CCTV camera on the screen viewable on the Teamviewer PC you remote into? Or do you arrange a time when a manager can be there to look at the screen and guide you?

Posted by Martin McCaffery (Member # 37) on 12-29-2017, 12:10 PM:

quote: Leo Enticknap
A telescope or a pair of binoculars (doesn't need to be fancy or expensive) is an essential toolkit item

My guy uses a gunsight. Works really well.
No, it's not attached to a gun during the operation.

Posted by Leo Enticknap (Member # 534) on 12-29-2017, 12:59 PM:

Given the behavior of many Hollywood actors recently, attaching it to a gun would be one helluva temptation when the movie is playing...

Seriously, though, that's a lot less bulky and easier to carry around than a pair of binoculars.

Posted by Frank Cox (Member # 6258) on 12-29-2017, 01:30 PM:

Gives a whole new meaning to shooting the colours...

Posted by Steve Guttag (Member # 268) on 12-29-2017, 02:24 PM:

I find most binoculars to be difficult on convergence and cheap ones near worthless. Cheap ones have enough chromatic aberrations that you tend to compensate for the poor lens. I'm a proponent of the USL/QSC VCC-102. Sure, I've used Binos or spotting scopes for quick adjustments but for serious work, particularly on NEC or anyone's Series 1 projectors, the VCC-102 is the right tool for the job.

We have made a tripod adapter for our Binoculars. Takes one thing out of your hand and holds it steady. Handy for bore-sighting/Scheimpflugging. Use the right pattern too. Barco got that right and much better than the rest. Use an All-green pattern with many targets...it isn't at either extreme of the wavelengths and the pattern is easy to see, even 4K.

Though no longer made (unfortunately), the PSA200 was THE tool for adjusting a cold mirror (looking for even light distribution).

Other handy tools are LONG tools. Some convergence systems require very long and small allens (and insulate them), NEC, for no good reason, doesn't include cap screws on their NC1200/NC2000 prisms to hold the settings so you need to have their adjusters BEFORE you unlock anything. Christie tends to make you want long screwdrivers and short ones. They often, now have the allens you need tucked away in the machine but don't count on them being there (not all came with them).