Screen Gain

[Linards Bartusevics]

To ensure optimal light intensity, the projector is running at 100%. After the 1/2 lamp warranty period, the FootLambert is too low (aprox.10FL). We use (it looks like) a matte screen with a reflection coefficient of 0.9. The problem is that the walls of the room are light-colored - a historical monument.
The idea of replacing a new screen with a reflectance of 1.4 GAIN. That way I get enough FL and probably the projector won't run at 100%. The question is, will the walls in the hall not be illuminated? Is there any formula for how much FL could increase if 1.4 is used instead of 0.9 GAIN.

[Carsten Kurz]

The screen gain will actually reduce stray light on and from the walls. It was a mistake to choose a projector/bulb combination so close to the necessary minimum. But, now I guess a mild 1.4 gain screen is the only solution.

1.4 means a gain of 1.4 - the center will see something like a 1.5 increase in luminance over a 0.9 screen. If you are now a 10fL you may just hit the 14fL spec.

What projector is it? No way to upgrade it?

- Carsten

[Linards Bartusevics]

I have only been working here recently. The choice and replacement of equipment was not up to me.
Of course I would like to get a new powerful laser projector and new sound, but it all depends on the investment. During a pandemic, I look what I can improve at a lower cost.
We are currently using a Kinoton DCP MX 30 II and more powerful lamp is not supported. Once a year, 35mm use too. Did I understand correctly that 35mm is not intended for a high gain level screen?
In this situation - a light round walls plus 35mm, plus digital projector could be a compromise for 1.4 gain. The idea is to replace a screen that is dirty. And get a better and brighter picture. And the screen would be compatible with the laser projector in the future

[Pete Naples]

Linards,

Has the projector been recently serviced and inspected?

On those Kinotons it's possible to dislodge the main mirror when fitting the lamp, that will kill the light output.

Also the condensing lens, I've seen those cracked (I can['t remember if MXII has one though)

At the age it must be, I would be advising replacement of the main mirror and possibly the fold mirror.

[Dave Macaulay]

I believe the light engine is essentially the same as in a Barco B series projector, Barco supplied the "innards" to Kinoton.
Do you have any records of screen image light level with new and aging lamps from when the projector was new? Brightness naturally diminishes as the optics age and collect dirt. The collector mirror loses reflectivity, and there are surfaces in the light pipe and folding mirrors that degrade. If the system used to be bright you should look for the reason and see if correcting it is possible (projector optics parts tend to be quite expensive).
Screens also age and get dirty. That will impact image quality and brightness. You don't say if this was an existing film installation that added digital projection that used the same screen for a long time previously.

Specifically, a gain screen is trying to direct the reflected light back towards the projector lens. This causes a "hot spot" in the image that appears where the viewing angle is closest to where you would see the lens if the screen were a mirror. A viewer at the side of a wide auditorium (typical for historical auditoria) gets a dimmer image overall that with a matte white screen, viewers on centreline get a brighter image. If the projection point is very high (again, typical in old multi-use auditoria) the hotspot will be high in the screen image and that can be a problem, tilted screens compensate a bit.
High gain screens can be greatl in some rooms, particularly long and narrow old single screen cinemas.

[Linards Bartusevics]

No, I do not have information on how bright the light was when the equipment was new. Of course, technology is aging, including optics and screens.
The target is to replace the projector in the future, so I don't want an expensive investment in this projector.
Something has been misadjusted in the past.
The projector had a cracked UV filter, a small control glass. Kinoton technician replaced the lamp igintion unit - it was necessary to remove, insert the mirror. I did not see any other damage. Well, the dust looked like it had never been cleaned of light engine, prism and other components. I did not see any other damage.
manuals I found that adjusting the mirror is quite complicated. So I initially decided not to change it. I am not sure that the technician has the knowledge to adjust the mirror and whether special tools are needed that are not available locally.
The screen is flat 11.5 m wide, 6.1 m high, distance 24.5 m. The space is basically round.

[Carsten Kurz]

What is the screen size? Alright. A gain screen has some negative implications, but, it's not that bad. Why would 35mm be an issue for a gain screen? We used a Harkness 1.6 gain perlux with our 35mm for 20 years. Very high gain silver screens (gain > 2) have a bad reputation (and rightfully so), but, a modern gain 1.4 white screen is nothing to complain about. Make sure you don't go for the cheapest possible screen. If the welds are visible, this will annoy the hell out of your audience. Within Europe, or, in Latvia, get Harkness.

Are you sure it is an MX 30 II Kinoton? Then what would be the problem with bulb choices? What bulb is currently installed? You need to find that out for sure.

[Linards Bartusevics]

I think there are 2 types of this projector. This projector has a maximum of 4.5kW with an existing mirror. Currently installed osram 4500W / HSLA OFR
The screen I wrote above is FLAT 11.5m x 6.1m distance 24.5m.
OK, overall I understand that a screen with a 1.4 gain will not have any negative effects and the picture would become brighter.
Note. With barco DP2K-32B after 6 years with a new mirror (change reason - lamp damage) the measurements showed +2 FL and the picture looked smoother. But right now I don't want to invest a lot of money in an old projector.

[Carsten Kurz]

There is DEFINITELY something wrong with the lightpath. A 4500W bulb should have ample light for this screen size, even if that screen is old and dirty. I guess a good projector inspection and maintenance should still be cheaper than a new screen of that size. That said, if the screen is actually old and dirty, it would certainly be a good idea to replace it anyway.

You should also check wether the lens is configured properly. There are ways to waste a lot of light if the lens is either not fitting the projection geometry, or the lens automation is broken. In that case, these projectors can be configured to project over the screen size, but scale the image down to the screen. This wastes a lot of light (and resolution). This has been done in some locations, sometimes with, sometimes without the owners/operators noticing it. You should be able to see the rectangular light spill around the screen though, when the auditorium is dark, and projecting a black image.

[Leo Enticknap]

Check the notch filter, too. I've seen them crack and cause significant light loss, especially in projectors with larger bulbs.

[Pete Naples]

Replacing the main mirror or fold mirror, or indeed any work which involves removing the lamphouse components requires optical re-alignment, which needs the facotry supplied alignment tool and the knowledge of how to use it. It's very critical.

Any Kinoton dealer should have the knowledge and tools to do this properly.

[Marcel Birgelen]

I think there are 2 types of this projector. This projector has a maximum of 4.5kW with an existing mirror. Currently installed osram 4500W / HSLA OFR
The screen I wrote above is FLAT 11.5m x 6.1m distance 24.5m.
OK, overall I understand that a screen with a 1.4 gain will not have any negative effects and the picture would become brighter.
Note. With barco DP2K-32B after 6 years with a new mirror (change reason - lamp damage) the measurements showed +2 FL and the picture looked smoother. But right now I don't want to invest a lot of money in an old projector.

Keep in mind that any "gain screen" will have "some negative effect", it will primarily increase hotspotting. Although, with a 1.4 gain and an otherwise decent setup, the effect should be minimal.

Still, a new screen isn't all that cheap either, and if you're running a 4.5k bulb at 100% at that screen size and still don't get enough light out of it, I'd say that any money would be better spent on fixing whatever is causing that light loss inside projector, rather than installing a new screen.

[Sascha Roll]

Also keep in mind that you absolutely DO NOT want to use a gain screen with a laser projector (that you will probably buy sooner or later, judging by the age of your equipment). It does not look good, not even acceptable IMHO. XBO 4500W should work with a new 0,98 Gain screen and the mentioned screen size.
A) Get a good technician and let him check and align everything
B) Get a new Matte White Screen (If you're Screen is curved: Go with Harkness 1.4 HiWhite)

PS:
C) In case you're having a DSS2(2)00 / IMB Cat745 installation (common for Kinoton installs) read the Thread in this forum...