Film-Tech Forum ARCHIVE: Lens issue on Barco 12c

This is topic Lens issue on Barco 12c in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Gavin Lewarne (Member # 5397) on 11-09-2015, 05:58 AM:

When our site was being serviced last Monday, our engineer noticed that when the motorised lens does any sort of zoom, it will come to its designated position and then "pulse / hunt" on the screen for a few seconds afterwards, ie, rapidly getting a bit smaller and then a bit bigger until it settles in the correct position. It does this for about 3 seconds.

I have been watching this very carefully over the last week and it does it every time there is any sort of lens shift or zoom movement.

As a VPF site, I reported it to DcineX and included a copy of the projector logs, which show no sign of any lens issue as far as the projector is concerned.

DcineX have come back to me and asked if I can swap the lens with a different projector, which is impossible as we are a single screen. While I deal with the run-around they are giving me, I was wondering if anyone has seen this before and what the likely culprit might be.

Lens: Fujinon 1.95 - 3.2
Projector: DP2k-12c
Projector Firmware - 1.13.190

The projection room and projector are kept impeccably clean, I check lens and screen alignments weekly, the lens was removed, contacts checked, and rehomed during the service which made no difference.

We also replaced a SMPS fan which necessitated the removal of the front cover, so we took the opportunity to inspect the lens holder - no obvious damage and everything was secure. Our lens settings are well within the shift boundaries so it isn't a case of it being "close to maximum" in any particular direction.

The projector has not been moved for months, no firmware changes, it just spontaneously started doing it.

cheers

Posted by Steve Guttag (Member # 268) on 11-09-2015, 06:09 AM:

This is normal (and goes on a bit longer in "B" series projectors). Barco tends to record every step it took to get the lens into position so it can recreate those steps when the format is called.

One of the things needed to get lenses to come to the right place is to allow for gear lash and ensure that the the same direction is used as it was when it was configured. That is, if you were moving the lens to the left when setting the position...the projector has to move the lens to the left when it puts it back there or any gear lash in the mechanism will introduce an error.

If you had a Christie projector, you would have noticed that when setting up the lens preset every time you switched directions, the lens controller moves the lens in the opposite direction first and then back to bias the gears in the direction you are going s that again, there is no gear lash.

Projectors that don't account for gear lash will inherently be less precise. Remember too, both sets of gear lash have to be accounted for..the motor and whatever servo may be used to "read" the lens position.

Posted by Gavin Lewarne (Member # 5397) on 11-09-2015, 06:14 AM:

Steve - the behaviour on ours is certainly outside what our engineer and myself deemed "normal". I am familiar with the little but of hunting when everything is ok, but this thing is pulsing rapidly, very rapidly which it never used to do and the effect is quite distracting on screen, as it continues to hunt position a good 3 seconds after its already moved to the right position.

Posted by Marco Giustini (Member # 4544) on 11-09-2015, 02:35 PM:

I noticed that too on two machines after a SW upgrade - both with Fujinon.
I reported to Barco but they said the lenses were faulty (both, after SW upgrade).

Maybe now they'll listen.