Projector placement for big scrim projections

GertjanB

Hi all,

I'm breaking my head over the placement of the projector for a big scrim projection (10m wide 5 or 6m high). On a tight budget.

I don't want any "left over projection going trough the screen" to fall on the back wall that is 5m behind the scrim.

If I calculate this I have to put the projector high up and very steep down so I lose a lot of the projection area. (I won't be having this hight every time and we don't have a budget to have enough ansi lumens I think)

An other option is to put it closer but then I have a big trapezoid. (0.8 lens in example)

When I try with two projectors I see the same problems. (a bit less)

What am I missing?

mark_m

@gertjanb said:

What am I missing?

Covering the back wall in Vantablack.

But seriously I don't think you're missing anything: the short distance - 5m - between scrim and back wall plus the width of the projection equals a difficult situation.

If the back wall is black (as in your diagrams) then covering that wall with black serge or something similarly unreflective will reduce the visibility of any spill.

Yes, using more projectors will help but the blending at that kind of an angle is going to be difficult.

Can you project on to the scrim from the sides, so that the overspill of projected light goes into the wings of the theatre?

Sorry, not that helpful

Mark (not that Mark).

kdobbe

If you have access to an ultra wide lens… You should be able to do this via rear projection. My Ultra Wide lens creates approximately a 2 to 1 ratio of width. So a 5 m distance will give a 10 m width… I am doing a project right now with very similar dimensions. Although, I have a front and rear projection screen, so perhaps the scrim might be problematic.

dbini

@kdobbe

which projector are you using to get an image 10m wide? most ultra-wide (mirror-based) systems have a throw ratio of about 0.2:1, but only go around 4m wide before they lose focus. i have a couple of old Optoma short throw projectors that have fixed lens at 0.5:1 but they are only 3500 lumens, so only suitable for projection up to around 6m wide in a very dark space.

dbini

@gertjanb

i would go for the widest lens possible and shoot the image from the grid straight at the scrim. if you try to go at a steep angle, you may have trouble focusing the image as the bottom of the scrim is nearly 5m further from the projector than the top of the scrim.
Using a 0.5:1 lens, or wider, will mean that your image on the back wall is going to be huge, and therefore less intense. If possible, rig some black molton curtains across the back wall - the wavy wibblyness will distort and absorb at least some of what's left of the image.

Also - a dense scrim like sharkstooth gauze will absorb more of the image.

GertjanB

I was thinking about a ultra short throw but didn't know the focus limitations.

I'm now thinking an a completely other direction. I will double the gauze above 2m50 this reduces the brightness of the light falling trough a lot.
This way the light under 2m50 can fall on the floor and the light above can fall on the back wall where we will use molton as suggested above (or if somebody has some spare Vantablack laying around :) )

Let hope this works.

Woland

@gertjanb said:

if somebody has some spare Vantablack laying around

There's this non-toxic alternative to Vantablack, but it's still expensive: https://culturehustle.com/collections/black?gclid=CjwKCAiAjPyfBhBMEiwAB2CCInIilPTnBfRjAXwar33ch72_1J42loCScRRC8VLEKtd7cyObs6iiHRoCeXwQAvD_BwE

bonemap

@gertjanb

Hi, not sure I can add anything else that is useful but, I have been working with a team designing a similar set for a show later in the year. All your concerns were reflected in the work we are doing. In this case there is a second scrim down stage that is proposed to have circular portals cut through it in three different places and front projection from the auditorium. Leaving that aside the upstage scrim is a full black sharktooth gauze. After looking at a few options we have decided to back project with the addition of a cyclorama rigged very close to the black guaze. This takes care of any bleed or shine through the scrim, and hides the cyc. I will use 3x 8000k projectors with short throw lenses flown from the back wall at about 4mtr to the cyc/scrim. This should give us a full width projection across the required 12 mtr. Would love to have a full width back projection screen but the cyc is going to be a bit of a compromise.

Best wishes,

Russell

dbini

@gertjanb

if you do this, the top half of the image will look brighter than the lower half - its better to double the scrim all the way to the floor.