NEC WT610 short throw projector hot spot

[leylandbobby]

Hi all, I'm looking to add a little video footage, some archive, some ambient via a Draper 8'x6' fastfold rear projection screen at the rear of the stage whilst the band is performing in front. (no drummer).

You will have guessed that the video content is not paramount to the show, but it will add to the overall presentation.

We play small to medium sized venues and the logistics of having the projector front of house is not an option.

I have trawled the interweb and am finding it difficult to find impartial reviews on the projectors available. Allbeit there aren't many available that boast extremely short throws...a must, as the longer the throw, the fewer venues I see us being able to incorporate the screen, by the time the band is set up there isn't usually much space left behind. Hence the NEC, billed as the worlds shortest throw, an impressive 8'x6' at less than a metre, 2000 ansi-lumens and 3500:1 contrast ratio. (it's times like this I wish I knew what it all meant) :** laughs out loud **: .....and it fits into my meagre budget of £1200.00.

 

I've looked through the other posts to see if I can get any help there and I see that I must beware of "hotspots" I am of course a total newbie and am assuming that a hotspot will be similar to holding a headlamp close up behind the screen.that won't do, so I was hoping that somebody can save me the cost of hiring one to see if it is indeed a problem with this particular projector.

Also, there are some stage lights 4 Martin SCX600's I would like to hang from the trussing above the screen, and a couple of moving heads, front of stage, plus 4 led par 56's, pretty much just used to light the guys in the band. I know the obvious things like not to let the beams hit the screen but do you think that we will still get some useful clarity from the screen.

We are not cash rich and although we would love to be able to incorporate the video side of things, we would ultimately prefer to avoid any unnecessary outlay.

I hope that I have given enough information, but if you need more please ask.

 

Thanks in advance. Dave.

[Pete McCrea]

The machine you have mentioned is specifically designed for use tight to the screen, so they will have taken hot-spotting into account in it's design.

 

Never having used one I can't vouch for the quality of the image or whether it does create hotspots though.

 

They are usually more of a problem when using a standard machine with a short throw lens and minimal throw distance.

[leylandbobby]

The machine you have mentioned is specifically designed for use tight to the screen, so they will have taken hot-spotting into account in it's design.

 

Never having used one I can't vouch for the quality of the image or whether it does create hotspots though.

 

They are usually more of a problem when using a standard machine with a short throw lens and minimal throw distance.

 

 

Thanks for that Pete...

[Johnparrack]

Hotspotting is usually down to the make up of the rear projection surface, I doub't very much that a projector will have been made to eradicate hotspotting...I might be wrong though!

Obviously the hotspot changes due to the viewing angle of the screen.

 

Usually in our field if we want to rear project and hotspotting could be an issue we don't want ..then we use a material called "Opera Blue" which is designed for NO hotspotting, and is usually used in widescreen softedged applications...eg Watchout, Encore, Montage etc etc

[leylandbobby]

Hotspotting is usually down to the make up of the rear projection surface, I doub't very much that a projector will have been made to eradicate hotspotting...I might be wrong though!

Obviously the hotspot changes due to the viewing angle of the screen.

 

Usually in our field if we want to rear project and hotspotting could be an issue we don't want ..then we use a material called "Opera Blue" which is designed for NO hotspotting, and is usually used in widescreen softedged applications...eg Watchout, Encore, Montage etc etc

 

 

Hi John, forgive the delay, thanks for that.

[soundo26]

Hot spotting is not to do with the screen surface but with the principles of optics!

 

This is a brief simplified explanation which is meant to be simple, there is a lot more to it and if you want to know more you should explore the theory of optics!

 

You will need to take a little more care with installation & setup when using short throw lenses, here are a few tips which may help you get the best although you must accept that the wider the lens, the hotter the spot and the less light output and more edge distortion you will get.

 

When using a standard lens, the light output is optimized pretty evenly across the width of the front end of the lens system. To the naked eye, the image will look fairly even across the whole image area but in reality, the image centre will always be brighter than the edges. When you use a short throw lens, the available light is dissipated over a much wider area, most of the main body of light is kept towards the centre section but the drop off towards the edges is much more pronounced, you will also find that there is more distortion in those areas too! This results in less light reaching the outer parts of the screen and softer focusing at the edges, the brighter centre is the hotspot that you mention. Using a short throw lens also results in less apparent light output overall because all the light is dissipated more. A higher quality optical system can reduce that a little but usually at massive cost.

 

When using short throw lenses it is very important to ensure that the image being output is coming through the centre of the lens, this can be seen if you stand just off to the side at the front of the projector at installation, you will see the rectangle of the image on the front of the lens, if you have used lens shift you may find that the image is high or low, you will need to ensure that it is centred. you will have to physically position the height of the projector ny raising or lowering the stand it is mounted on. try to keep both the vertical & horizontal aspects of the ratio true between the projector & screen, it will not help you if the path of light is skewed in any way as as keystone, pincushion and skew adjustments are all much more difficult to resolve at shorter distances. if you have to raise the front of the projector up to frame it within the aperture you will be better off to raise the whole projecter higher and lower the front or raise the back as you will want as much light going towards your audience as possible. It will be no good to have the projector behind the screen pointing towards the ceiling when your audience is below the screen level, they will only see the peripheral light, not the main body which will be seen more clearly be anybody up in the balcony, point the light toward the audience.

[Stegga]

It might also be worth looking at this, the Hitachi CP-A100 - CLICK - designed for educational use but I am told they are very good. At 2500 lumen it should be bright enough, if like you say, you avoid spill from the lights as much as possible. It looks like these retail at just over a grand.

hope that helps, Sam