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Author Topic: Motorized Lens Question
Muhamad Taufiq
Film Handler

Posts: 13
From: Bandung, Indonesia
Registered: May 2015


 - posted 01-27-2018 09:20 AM      Profile for Muhamad Taufiq     Send New Private Message       Edit/Delete Post 
I just get back from my favorite studio and I noticed they changed the projector from CP42xx to Barco B-series. After the trailers finished, the masking opens up and I can see the lens' zoom following. They start the Atmos trailer and the images is out of focus, the adjustment is very slow, a few seconds after the start of the movie the images is finally in focus. I did not think much at the time, probably just some glitch. But at home I remember that at Barco's website there are certain lens that didn't mentioned as motorized, and it possible that the projectionist had to adjust focus when there's image on screen (Atmos trailer).

So my question: is there really are lens that are not motorized? Because I find this hard to believe, since I think it should come as a standard, especially considering the price of cinema lens.

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Dave Macaulay
Film God

Posts: 2014
From: Toronto, Canada
Registered: Apr 2001


 - posted 01-27-2018 11:04 AM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
I think there are a few Barco B lenses that are not motorized but I've never seen one.
Barco series 2 lens motors move pretty quickly, and all motors move together (focus, zoom, and shift). I sometimes see the image adjusting after a format change but normal practice is to insert a few seconds of black in the playlist to hide it.
Are you sure they didn't get a series 1 projector? These moved one motor at a time - and not very quickly, format change can take quite some time depending on the amount each motor has to move. If an image is onscreen you see each adjustment in sequence, on a S2 unit the image zooms and shifts simultaneously while also refocussing.

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Stephan Shelley
Jedi Master Film Handler

Posts: 594
From: castro valley, CA, usa
Registered: Nov 2014


 - posted 01-27-2018 12:25 PM      Profile for Stephan Shelley   Email Stephan Shelley   Send New Private Message       Edit/Delete Post 
I can state for a fact that the Barco B series focus is very slow. It is not done in the lens like the C series it moves the lens mount in and out something like the Christie 20 and 30 series but much slower.

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Dave Macaulay
Film God

Posts: 2014
From: Toronto, Canada
Registered: Apr 2001


 - posted 01-27-2018 01:10 PM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
Focus is slower than zoom and shift, true. And there's an adjustment for reducing image shake that adds drag to the focus movement and slows it down. They should insert a black segment for the duration of focus adjustment. This must have a pretty severe zoom between formats, focus shifts a bit on zoom but not a crazy amount. Some lenses are worse than others for focus change with zoom change.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 11913
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-27-2018 01:55 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
A couple of things:

Barco lens adjustments are MANY times slower than Christie. Christie lens adjustments are VERY VERY VERY fast (1-2 seconds, tops for the most radical of changes.

MOST Barco B series lenses use the Barco lens mount for the focus but there is an Invision model that also has its focus in the lens (when that lens is selected and the projector is homed, the lens mount will move in and then count out to set position and never move thereafter (until the next home/return). (Part R9856300, Zoom lens 2K:1.82-2.86/4K:1.65-2.60) Note, I was not that impressed with the lens. In the recent installation I had with it, it had a VERY narrow depth-of-focus sweet spot. I spent quite a bit of time getting it optimized over the entire screen and even then, I wouldn't consider it great. Minolta remains my preferred DCinema lens manufacturer but Barco seems to be moving further away from them and more into InVision, which really vary a bit from unit-to-unit.

But back to the description of the problem observed. Presuming an InVision lens (highest likelihood based on available lenses), when the image is zoomed, the image will go into and out of focus multiple times on a typical Flat to Scope zoom. It is the strangest thing. Most lenses, if there is a focus differential between Flat and Scope, the focus difference gradually moves in one direction. Not so with the InVision. Note, if you want to spend the time, setting the backfocus on a site-by-site basis one can minimize and sometimes eliminate the need for refocusing (at least on normal lenses, I don't know about InVision).

The Barco B lens mount is the slowest of the bunch but not to the "drag" as Dave alluded to (there is "pressure on the top of the mount but not enough to bind it or it would see-saw its way back and forth and be completely unpredictable...though it is close). Incidentally, there is a VASTLY IMPROVED lens stabilizer that Barco refuses to incorporate into production. Instead of applying pressure to the top, one affixes a linear bearing arrangement that prevents the mount from moving in anything but the Z axis and thus gets rid of the vibration. I HIGHLY recommend it. It effectively eliminates most of the B stability/focus issues (that are not lens born problems).

So based on the description, I can easily believe that one would have seen the image, as it was zoomed (which moves relatively fast) go out of focus and then it take several seconds for the focus to "catch up" to the rest of the lens motion. The lens would typically need to shift up a little (have almost no lateral shift, quite a bit of zoom and depending on the lens and back focus, a bit of focus to do and on a Barco B, Focus is the the slow one if there is a substantial movement needed (the shift motors are the same speed as focus but as described above, they don't have as much to move).

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Stephan Shelley
Jedi Master Film Handler

Posts: 594
From: castro valley, CA, usa
Registered: Nov 2014


 - posted 01-27-2018 03:24 PM      Profile for Stephan Shelley   Email Stephan Shelley   Send New Private Message       Edit/Delete Post 
An install I did at a drive-in with a DP4K-32B, 100' by 40' screen around 200' throw it would take close to 50 seconds to go between scope and flat.

NECs are no speed demons either.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 11913
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-27-2018 03:53 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
While reading Stephens description, it dawned on me that for a "B" projector, if the focus isn't in the lens itself, then there is no "back focus" per-say since the lens mount is doing the focusing by moving the entire lens.

So what is taking 50 seconds? The focus?

We have a DP2K-32B in Maine and it definitely doesn't take that long.

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Stephan Shelley
Jedi Master Film Handler

Posts: 594
From: castro valley, CA, usa
Registered: Nov 2014


 - posted 01-27-2018 04:56 PM      Profile for Stephan Shelley   Email Stephan Shelley   Send New Private Message       Edit/Delete Post 
It was mostly the focus. There was a fair amount of zoom going on. The image was going from 100' wide to 74'. Plus we were at the limit of the zoom at one end. That is a fine thread on the adjustment screw of the focus. I remember at Barco school it would take a long time to focus. It would seem for a long time nothing was happening as the movement in and out if very slow. A lot of turns to get much movement.

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Muhamad Taufiq
Film Handler

Posts: 13
From: Bandung, Indonesia
Registered: May 2015


 - posted 01-27-2018 04:57 PM      Profile for Muhamad Taufiq     Send New Private Message       Edit/Delete Post 
Dave - I'm pretty sure they didn't install series 1, as this studio is equipped with Atmos so it need to handle SMPTE DCP

Steve - I have watched on lots of Barco B-series and I don't mean the focus adjustment is a little bit slower than Christie, but much much slower, about 30 seconds (or more if you count the black screen during masking opening). I measured the studio to be about 15,26m x 20,71m (50' x 67,9'). The focus does not moves in and out, instead it moves gradually during those 30 seconds.

Actually the point of my original question is whether this is something that was not done correctly by the installer or limitation from the equipment itself?

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Magnus Eriksson
Expert Film Handler

Posts: 107
From: Stockholm, Hägersten, Sweden
Registered: Jan 2011


 - posted 01-30-2018 11:38 AM      Profile for Magnus Eriksson   Email Magnus Eriksson   Send New Private Message       Edit/Delete Post 
quote: Steve Guttag
Incidentally, there is a VASTLY IMPROVED lens stabilizer that Barco refuses to incorporate into production
Steve, do you know the part number (R-number) for that contraption? I really need one of those.
Last time I ordered a lens stabilizer from Barco I recieved the "old" model. Since the projector already had one of those mounted when delivered from the factory it didn´t help very much [uhoh]
/M.E.

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Carsten Kurz
Film God

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From: Cologne, NRW, Germany
Registered: Aug 2009


 - posted 01-30-2018 01:18 PM      Profile for Carsten Kurz   Email Carsten Kurz   Send New Private Message       Edit/Delete Post 
Muhamad - yes, there are actually quite a few places with non-motorized lenses, simply because you don't need a motorized lens for the typical flat/scope change on constant width screens.

But, those manual lenses are certainly never used with the idea that a projectionist always adjusts the lens at format changes as one would have done often in film days. Of course, it is possible that some projectors suffer from a drift issue and can not reach a proper position and focus automatically. I know some cinemas resorted to adjusting the lens after the lens movement came to a rest until the issue was fixed and fully automatic lens adjustment was restored. You may have seen something like that.

Usually, when format changes are programmed into the show playlist, the light dowser is closed so the audience can not see these changes on screen. That usually involves putting 5s-30s of black into the playlist, during which the lens and electronic changes are performed invisible. Some projectors/lenses are extremely slow. Maybe in your case they forgot to close the dowser or to insert the black into the playlist. While the installer will usually prepare and explain these issues to the operators, it is the operators duty to stick to these schemes in order to have a flawless presentation.

- Carsten

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 11913
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-30-2018 05:22 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Carsten,

On your places that don't move the lens due to a constant width screen...do they scale the scope image down to fit the width? Do they merely crop everything to 1998/3996 pixels?

Magnus, I'll get you the part number tomorrow...I'm out today.

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Muhamad Taufiq
Film Handler

Posts: 13
From: Bandung, Indonesia
Registered: May 2015


 - posted 01-30-2018 05:36 PM      Profile for Muhamad Taufiq     Send New Private Message       Edit/Delete Post 
Thanks everyone for your explanation.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 11913
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-31-2018 10:22 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
The improved lens stabilizer from Barco is the R9856618. Barco calls it a "Shock Improvement Kit." I call it, essential for MOST installations. With some of the smaller Minolta lenses, it hasn't been so bad. With the heavy as sin InVision lenses, it is pretty much a must.

Be forewarned, it is NOT a cheap part (multiple hundred $$$US) but perhaps you can shame them into supplying it for you.

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Magnus Eriksson
Expert Film Handler

Posts: 107
From: Stockholm, Hägersten, Sweden
Registered: Jan 2011


 - posted 01-31-2018 02:21 PM      Profile for Magnus Eriksson   Email Magnus Eriksson   Send New Private Message       Edit/Delete Post 
Well, let´s hope it also improves the shock when the end customer sees the price tag...
This site has long throw and a really long and heavy lens. The image has been shaking since the projector was installed.
Thanks Steve, I will give Barco a call.
/M.E.

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