Projector brightness for long throw

[johnb]

Hi

 

I'm hoping someone might be able to help me with something that feels like there should be an easy way to work out, but I can't seem to see it at the moment.

 

Currently we use a standard 3000 lumen portable projector to fill a screen about 2.5m wide from about 3m. This is bright enough for our needs, although slightly brighter would be nice.

 

Currently I'm trying to get an idea of budget required to go over to a long throw setup. This would need to reach the 2.5 to 3m screen with a throw of about 13m, making it quite a long throw. The question I have is how bright do I need to achieve a similar level of brightness to the current setup. This feels like something that ought to be calculate-able, however I can't work out how. Does anyone know a sensible way of working this out?

 

Cheers

John

[Steve Cavill]

Do you have the contrast ratio to hand at all for the projector in question?

 

A 13m projection distance is quite large, although, I have a stock of Epson EMP-8150's which are 3200 lumen, and are able to handle a 12m projection distance with a Long Throw Zoom Lense installed.

[Tom Baldwin]

If your projection size isn't changing, the lumens you need from the projector doesn't change either, regardless of throw.

You might find very long lenses are slightly less efficient, but not by much.

[johnb]

Thank you for the quick responses. The current projector has a contrast ratio of 1500:1

 

If your projection size isn't changing, the lumens you need from the projector doesn't change either, regardless of throw.

You might find very long lenses are slightly less efficient, but not by much.

 

That was what I was missing - I couldn't work out if it should reduce with distance or stay the same.

 

Now I see some googling coming up to find some suitable models and sample pricing.

 

Cheers

John

[henny]

as tom has said above your screen size is not changeing so you still have the same amount of light hiting the same area just at a diffrent focal lenth.

 

what you need to know when shoping for a projector is the focal lenth of the lens you need.

 

Focal lenth = Throw / image with

 

so

 

12m / 2.5m = 4.8

 

you may see it written as 4.8:1

 

at that you are allmost certainley loking at a projector that has interchangeable lenses as most that have a fixed lense are some where between .8:1 and 3:1

 

projectors with interchangeable lenses cost a good bit more. but they tend to be better more "PRO" units, you tend to get no lense with it and have to pay sepereatley for the lense you want. also they tend to be 5000 ancii +

 

take a look at Sanyo PLC-XM100L and the LNS-T20 - Lense this would give you throw of 11.49M from lens

 

sanyo has a usefull tool for working out projector/lens combos see lens calculator?

 

cheers

 

ian

[kitlane]

The f value of the lens may help. The f value is the ratio of the focal length to its diameter. The smaller the f number the more light is passed.