long or short throw

[henny]

I have an install on the horizon , a large 6 x 4.5m front projection screen. will be using something like a sanyo PLC-XP57 5,500 ANSI lumen's. the problem I have is if I was to go short throw about 7.5m I would be looking at having to mount it on a 6-8m drop pole from the foh ceiling (that's 14m up). I have another option of using a long throw lens and projecting from about 27m away with the projector fixed directly to the ceiling of the foh control position.

 

the second option would be the easer to install and mentain but what would I loose in brightness? I gut says it would be the same cos the same amount of light out of the projector on the same area screen. but you must loose something over that distance ?

 

cheers

 

ian

[lukemh]

I have an install on the horizon , a large 6 x 4.5m front projection screen. will be using something like a sanyo PLC-XP57 5,500 ANSI lumen's. the problem I have is if I was to go short throw about 7.5m I would be looking at having to mount it on a 6-8m drop pole from the foh ceiling (that's 14m up). I have another option of using a long throw lens and projecting from about 27m away with the projector fixed directly to the ceiling of the foh control position.

 

the second option would be the easer to install and mentain but what would I loose in brightness? I gut says it would be the same cos the same amount of light out of the projector on the same area screen. but you must loose something over that distance ?

 

cheers

 

ian

Ian for picture quality the best lens is usually not the .8:1 this is because it magnifies the image and thus result is poor focus in the corners and the edges therefore I would go long throw.

 

dont forget it is more important about the light hitting the screen more than the light passing through the projection path.

 

BTW what is a Sanyo????

[henny]

BTW what is a Sanyo???? :** laughs out loud **:

a make of projector for when ones clients dont have the cash for a DP or Christie unit

[lukemh]

BTW what is a Sanyo???? :** laughs out loud **:

a make of projector for when ones clients dont have the cash for a DP or Christie unit

Touche! surely thats what ex demo projectors are for!

 

and I thought DP C****** and the S word were all different names for the same projectors

[soundo26]

As posted by luke from Barco the shorter throw lenses have focus drop off at the edges of the lens, if you do use a short throw lens it is very important to get the projector on the correct axis and to check that the image is passing through the centre of the lens (if you have used lens shift it probably isn't), you can see this if you look at the front of the lens (Not directly into it though).

The other bigger problem with short throw lenses is that because they are wide angle, they dissipate the available light and cause lots of light to be wasted to the point that it is often better to use a narrower lens from long distance than to use a wide lens from a short distance, you will also get a hotspot in the centre of the screen if rear projecting, always use longer throw lenses where possible

[Pete McCrea]

As Soundo26 says using the short throw lens gives hotspots on the screen. All things being equal, and assuming that there are no losses in the long throw lens, then you should get 5500 lumens on the screen. There was a post in the lighting section explaining the effects of distance and image size quite recently, more aimed at lighting but still very relevant.