Projecting through light

[DSA]

Hi,

 

We are doing 'Animal Farm' as a lower school production next week, and the rigging is happening tomorrow.

 

Speaking to the Director today, he is having a projection from our balcony onto our proper projection screen using a 'normal' computer projector (well a school one, so nothing too fancy). This apparantly is on for most of the show.

 

The performance is happening in the 'semi-round' - that is the actors act from front edge of stage onto floor space with rows of audience on the three sides (not stage side of square).

 

As a result I see most of the lighting coming from our perches to side light, and a bit of toplight from lx bars overhead in the auditorium.

 

The director asked me a question, and I didn't know the answer so I said I would find out....that is, Will the projection be affected in any way by going through the main light beams (from the perches especially)? If so, how can I be careful about this when rigging? Is it going to be a massive problem? Do I need to therefore rig the projector up on a lx bar (to get height)?

 

Thanks in advance,

David

 

P.S. Sorry it was a toss up with the ligting or AV forum......I hope this is OK, mods!

[paulears]

in fact, the front on projection is geometrically the best - no keystoning, although if it's a modern projector, it will have some adjustment for this. The main snags with low level source are not the beams interacting - they'll go through each other fine if they're not in the same plane, but the low angle means the actors will cast big ugly shadows on the screen. Spill light is the usual main problem - you have to leave a 'dead' area in front of the screen. floor reflection can mess the image up too. side light, being 90 degrees off should make this less of a problem.

 

Is there a plan 'b' in case it doesn't work. last show I did with projection it failed miserably and got removed in tec, because no one tested it before and on stage lights for the musicians all faced u/s and washed it out - even with gels, dimmer lamps etc - just too much reflected off the sheet music. A brighter projector might have done the trick, but not enough time to try it out. The issue was that the projector had to be a certain distance away to get the image size needed, and this was too far to be bright!

[DSA]

Just remembered of course that the screen will do rear projection, so that may be a solution. However I seem to remember from past experience that one cannot get a very large picture on the screen without hitting the backwall first!

 

Has anyone any solution to this. I could rig it higher than stage level.....would that help (trig says it would be a further distance etc.)

 

Yes, will have to watch out for spilled light...its very bad off our screen....

 

Best Wishes,

David

[smeggie]

big holes in the wall are not an option then? ;)

 

if there is time to experiment, the use of a mirror could be of use at 45 degrees to the image as far back as possible -

 

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kinda?

[Pete McCrea]

If it's a half decent projector, then there may be the possibility of fitting a short throw lense. Get a decent ratio, and you could do 8' wide with a throw of about 4'. Use that on a good rear project screen to maximise brightness.

 

Best bet is to make sure the focus is tight with little spill or reflections on the screen. And the max brightness projector available. I think the boys at USS have the a Christie LX41, and short throw lenses. Nice and bright.

 

Little DJ

[MikeR]

Rear projection is by far the best way to go if you can - this minimises ambient light because you will make it as dark backstage as possible. Its also far easier to set the projector up in the correct position to have the picture geometry spot on - ie no need for a projector on a stand at head height in front of the screen in the middle of the audience and no requirement to adjust for keystoning caused by flying the projector. If you cant change the lens for something like a 0.8 short throw lens & your throw distance is too short to fill the screen you can either move the screen forward which may not be possible or project off a mirror. Using a mirror is not that easy and if you havent done it before you will need plenty of time to experiment with angles & positions the correct combination of which will give you an as accuarate picture geometry as possible. You will need a means of supporting the mirror & isolating it from vibration caused by loud sound sources which may or may not be an issue. Additionally you will also need a rear projection screen you can hire them quite cheaply from lots of suppliers. On the subject of distances

you could do 8' wide with a throw of about 4'

Ive not come across a 0.5 lens myself, and I imagine that the picture would be horribly bent and twisted at the edges, nor would you be able to correct the distortions caused by an extremly short focal length. In general screen width x focal length = throw distance (+ a further few feet for the depth of the body of the projector). Using a mirror does not require that the mirror is as far back from the screen or the lens as possible, distances in this case are reliant on the surface area of the mirror in relation to the screen & angles relate to the amount of keystoning you get at any given distance from the screen.

[Guest lightnix]

The projector beam will not be affected by shining through the beams from the lighting rig, but the image on the screen will almost certainly be affected by reflected / ambient light (or "bounce"). As MikeR says, definitely go for rear projection if possible, as this will be least affected by the above, although care will still be required with the focussing of the lights to avoid having them shine onto the screen. Bright / glossy stage surfaces are also best avoided.

[mike]

The performance is happening in the 'semi-round' - that is the actors act from front edge of stage onto floor space with rows of audience on the three sides (not stage side of square).

 

just for info.... we usually describe this kind of stage set up as thrust. Although, all credit for making yourself perfectly well understood

mike

[iZian]

Just remembered of course that the screen will do rear projection, so that may be a solution.  However I seem to remember from past experience that one cannot get a very large picture on the screen without hitting the backwall first!

Hi Dave,

We will have the problem (if we put it B/S) of actors walking in front of the projection as they need to get from wing to wing behind the screen. This would cause obvious problems.

 

I think our best bet is to have the projector on the balcony (if ROS hasnt allocated the seats there to an audience) and arrange the lights so we can dim the lights that give us the most spill onto the screen.

 

Also, we are (as you said) using most of the lights from the side, so reflection at that angle still there, but much less sever due to the angle, than that given by the lights from above.

 

Four legs good, Two Legs Always Better Tho !

[P. Funk]

or you could put a ramp over the projector backstage?

[MikeR]

If youre using a mirror to project off then there would most likely be walkway space behind the mirror installation. Just a thought. Alternately you could dig a tunnel under the projector - more fun than a ramp after all.

[robloxley]

Usually you'd rig the projector above head height or far enough downstage to give an upstage cross-over if needed. As for mirrors, ours bolts to the upstage wall to reduce vibrations.

[iZian]

Well, we have (or the people running the projection have) decided that it will be ok to run the projection from the balcony so that it shines in the actors faces and looks a state.

Oh well, c'est la vie. :D