Ultra short throw .25:1 projector doesn't exist

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Mar 6, 2016
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BC Canada
A few years back we purchased an Optoma ultra short throw projector with a throw ratio of .25:1 We mounted this as far away from our cyc as possible (about 9', right against the upstage border) which created an image that filled our cyc side to side and does a fair job on height. This has proven extremely popular and useful for everything to plays and variety shows to bands and children's theatre, dance. The uses are endless. The only shortcoming has been the Lumens (4000) We are ready to upgrade to a professional projector but are surprised to find a powerful projector with the throw ratio we need (small theater) .25:1 doesn't even exist. Has anyone heard of a company that will do custom work? Is there a product out there I missed? The lenses exist and projectors exist but no one sells them put together. Thanks!
 

ruinexplorer

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Yes, you could get a custom lens made, but the cost would probably be prohibitive. I agree that ~.35 is the shortest throw that you will get for a brighter projector.
 

NateTheRiddler

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*raises hand* I’ve a question for the projection experts around here.

For my own learning: why would such a short throw not be possible with a more powerful projector? Size? Optics? Heat? Prohibitive expense? I understand that the extreme lenses (<0.5 or >5 ratio) are considered extreme for a reason, and the long throw makes sense to me... you can only throw light so far before it diffuses into the environment. But why is short throw more complicated?

(As for RTFM, I’m still waiting for my “Understanding Projection” textbook to arrive)
 
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Ancient Engineer

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why would such a short throw not be possible with a more powerful projector?
Nate, the real issue is lensing. It is difficult to make a wide lens that is even in its transmisson and not distorted.

It usually ends up being either a lot of elements (which suck up photons like a shop-vac) or a specially designed aspherical achromat doublet that involves expensive polishing/coatings to keep the edges straight.

Because most projectors use a transmission type of LCD there is already inherent losses and the photons passing through are not as fabulously parallel as we'd like. So, we end up with "conditioning" optics to assist the photons in being parallel before hitting the objective lens.

All this adds up.

So, if you are a manufacturer in 2019 and you sell, lets say 100,000 projectors a year, and 17 of those need all this expensive optical "help" to make a short-throw, clean, evenly lit, square image...

Suuuure you want to serve all possible customers. But you still have to make money to eat...

So, the really expensive solutions (like Barco) figure that if you need it, you'll pay for it.

They are mostly right...



P.S. A great example of this is the relative cost and design difference between a Fresnel and a PAR can.
The Fresnel provides an even wash but is expensive and has many elements.
The PAR can (presuming a WFL) provides a even-ish wash (OK, its awful, that !#%$ football hot-spot)and it is super simple to construct and is cheap.
 
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RonHebbard

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Waterdown, ON, CA
Nate, the real issue is lensing. It is difficult to make a wide lens that is even in its transmisson and not distorted.

It usually ends up being either a lot of elements (which suck up photons like a shop-vac) or a specially designed aspherical achromat doublet that involves expensive polishing/coatings to keep the edges straight.

Because most projectors use a transmission type of LED there is already inherent losses and the photons passing through are not as fabulously parallel as we'd like. So, we end up with "conditioning" optics to assist the photons in being parallel before hitting the objective lens.

All this adds up.

So, if you are a manufacturer in 2019 and you sell, lets say 100,000 projectors a year, and 17 of those need all this expensive optical "help" to make a short-throw, clean, evenly lit, square image...

Suuuure you want to serve all possible customers. But you still have to make money to eat...

So, the really expensive solutions (like Barco) figure that if you need it, you'll pay for it.

They are mostly right...



P.S. A great example of this is the relative cost and design difference between a Fresnel and a PAR can.
The Fresnel provides an even wash but is expensive and has many elements.
The PAR can (presuming a WFL) provides a even-ish wash (OK, its awful, that !#%$ football hot-spot)and it is super simple to construct and is cheap.
@Ancient Engineer @NateTheRiddler and @BC Theatre Guy Posting in FULL support and mentioning: All of the above is in addition to having a projection surface accommodating the projection and viewing angles required since your projector is now striking your screen at an extremely oblique, glancing, angle. 'nough said?
Toodleoo!
Ron Hebbard
 
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Ancient Engineer

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having a projection surface accommodating the projection and viewing angles
Ya mean my brand-new California King Sized white bedsheet won't be awesome...

Hmph.

Yes yes yes RonHebbard! The laws of physics are grumpy bastards when we ask for an omni directional reflective surface that takes a single input angle and gives every exit angle...

Wait...

3M Scotchlight 5100 takes incident light and gives it back at nearly every possible angle.

;)
 
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macsound

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Jun 15, 2018
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San Francisco, CA
Another thing to look at and realize are lens ratios don't match as you change chip size and resolution.
So maybe these newer projectors different lens ratios match the old ratios, but differ because the chip is 1080p and maybe the old ones were just emulating 1080p but were actually 1024x768.

Also, smart board projectors
 

porkchop

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A company I toured with owns a gigantic mirror for when they come across this problem in smaller European theaters. It was big and awkward and a large sheet of glass is rarely a good idea in theatre, but it survived in the trucks so with some precautions one could probably survive in a permanent space.
 

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