# Reverse Projection Question



## thorin81 (Oct 8, 2007)

I am getting ready to do a show that needs some projections to come up on the cyc that is about mid-stage. My problem is that I don't have the foggiest idea how to set up the projections to rear project since they will be living behind the cyc. Anyone have any suggestions?

Thanks!!


----------



## Footer (Oct 8, 2007)

Its pretty simple, most projectors have a few different settings, rear projection, underhung, etc... switch the projector to rear projection and you are set. Every projector I have came across has these settings.


----------



## jonhirsh (Oct 8, 2007)

Are you asking how to physicaly set up the projector?
or what settings to use?
I have included a drawing of a projector set up for rear projection. It is set up on a standard scaffold at the center of the screen. 
JH


----------



## Footer (Oct 8, 2007)

This topic has been discussed before as far as the physics of the whole thing goes.....

http://www.controlbooth.com/forums/showthread.php?t=4359&highlight=projection+mirror


----------



## SerraAva (Oct 8, 2007)

Also be aware that a rear projector on the cyc or scrim will have a spot which you can see a 'hot spot'. Depending on what and how you are projecting, you can get rid of it by actually blocking the 'hot spot' with a piece of wood. Just have someone stand in front of the cyc and say when they can't see it anymore. This however might lower intensity and possibly block images. Also depends on how bright projector is too. 

Is front just not an option? When I was orginally planning for Ragtime, we were going to do 2 rear projectors with .8 lenses. Instead, we ended up doing front with one, more powerful projector. Also gave us more stage space which the director kept whining about.


----------



## kwotipka (Oct 8, 2007)

If you can put the projector at the bottom of the screen and then correct the keystone, that will get rid of most of the hotspot. Most of the new projectors now have really easy keystone features. Try not to rely on them too heavy though because it will degrade the image a bit.

kw


----------



## SerraAva (Oct 8, 2007)

Lol, I was going to suggest really high if the projector had enough keystone. But it all depends on a number of things. So if you have the projector, try it out in a bunch of different ways and see what works best. If not, make sure you can play with it for a little bit to get it set up properly.


----------



## museav (Oct 9, 2007)

The positioning depends greatly upon the lens and the relationship to the audience, as well as practical considerations such as how you can mount the projector.

Most very short throw lenses (<1.0:1) rarely have any keystone correction capability and defeat any lens shift functionality, thus almost always requiring that the projector be on the centerline of the image with those lenses. Most other lenses will have the projector ideally located near the top or bottom of the image.

If your audience area is sloped up away from the screen then consider putting the projector towards the bottom of the screen. If the audience area is flat or below the screen, then having the projector towards the top of the image may work better. However, the projector location is often dictated more by practical considerations than it is by technical ideals.

Somewhere in the projector's on-screen menus is probably a projector configuration option. Typical selections would be front projection tabletop, front projection ceiling, rear projection tabletop and rear projection ceiling. If you can't find this and don't have the projector manual, you can usually find manuals somewhere on the manufacturer's web site, typically either with the product data or under technical support.


----------



## kwotipka (Oct 14, 2007)

Ever had one of those times when your advice comes screaming back at you? 

I must have missed the previous post. What they said.

kw


----------



## PhantomD (Oct 26, 2007)

We have an installed rear projection system with a projector in a drop-box and a rigged screen.

I can say that if you place the projector level to the top of the screen and use minimal keystoning, the image hotspot will not be noticeable except for those who are directly level with the screen.


----------

