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Projector to light a 150" screen

Projector

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48 replies to this topic

#41 of 49 OFFLINE   Barry Tonner

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Posted September 26 2014 - 03:52 AM

Well, one of us is correct and the other one isn't.

 

Your comment:  [color=rgb(40,40,40);font-family:'Merriweather Sans', sans-serif;background-color:rgb(242,242,242);]The throw distance, has no bearing on the brightness of the image[/color]

 

Is not correct. 

 

While the TD itself will not cause a direct difference in light output, how the internal optics of the lense deal with the throw distance (to maintain the same screen size) will cause a difference in light output. 

 

I guess if you are wanting to have a purely semantical argument on throw distance, then you would be correct, but not correct if you want to factor in how the lense deals with the increased mechanical zooming of the optics. 

 

Perhaps I was mis reading what you were trying say? Not sure, Im currently on pain killers :-) 

Thanks for the response Gregge..it's nice when one can have an intelligent discussion about a subject.  So you are saying it is the optics that are changing the brightness, not the TD!...that sort of proves my point.  I would still say....using the same lense, keeping the image the same size, and moving the projector further away, does not diminish the brightness of the image.  Try it sometime...you'll see.



#42 of 49 OFFLINE   Gregg Loewen

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Posted September 26 2014 - 04:37 AM

 

[color=rgb(40,40,40);font-family:'Merriweather Sans', sans-serif;background-color:rgb(242,242,242);]does not diminish the brightness of the image.  Try it sometime...you'll see[/color]

 

I try it all the time. It is what I do for a living. 


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#43 of 49 OFFLINE   FoxyMulder

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Posted September 26 2014 - 07:11 AM

using the same lense, keeping the image the same size, and moving the projector further away, does not diminish the brightness of the image.  Try it sometime...you'll see.

 

I have a meter to measure all this, it does diminish brightness but our eyes are very forgiving of this, they adapt to changes quickly.


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#44 of 49 OFFLINE   Chuck Anstey

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Posted October 02 2014 - 06:32 AM

I would still say....using the same lense, keeping the image the same size, and moving the projector further away, does not diminish the brightness of the image.  Try it sometime...you'll see.

This is an incorrect statement.  A projector with a zoom lens will have the brightest image for any given size screen if it is located as close as possible (max zoom) for that screen size.  This is very well understood and good projector reviews will state the output and contrast at max zoom and min zoom (max distance and still maintain screen size).  The advantage of putting a projector at the maximum possible distance for a given screen size is an increase on on/off contrast ratio at the cost of some light output.



#45 of 49 OFFLINE   schan1269

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Posted October 02 2014 - 06:36 AM

This is an incorrect statement.  A projector with a zoom lens will have the brightest image for any given size screen if it is located as close as possible (max zoom) for that screen size.  This is very well understood and good projector reviews will state the output and contrast at max zoom and min zoom (max distance and still maintain screen size).  The advantage of putting a projector at the maximum possible distance for a given screen size is an increase on on/off contrast ratio at the cost of some light output.

And the image is sharper. Light is straight as possible.

#46 of 49 OFFLINE   Gregg Loewen

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Posted October 02 2014 - 06:43 AM

 

[color=rgb(40,40,40);font-family:'Merriweather Sans', sans-serif;background-color:rgb(242,242,242);]And the image is sharper. Light is straight as possible. [/color]

 

Actually, the opposite is true.


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#47 of 49 OFFLINE   Gregg Loewen

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Posted October 02 2014 - 06:50 AM

the closer a PJ is to a screen, the brighter the image (usually). 

 

The closer a PJ is to a screen the worse focus, uniformity and potential chromatic abberations occur. This is due to the image being projected through more surface area on the lenses. There is always more distortion on a lense as you move away from the middle of it.


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#48 of 49 OFFLINE   schan1269

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Posted October 02 2014 - 06:52 AM

I think Chuck has zoom backwards.That is where that comes from...Straighter light, sharper image at less zoom.Nevermind...re-read agan...(just got up from a 12. Another 12 today...)

#49 of 49 OFFLINE   Chuck Anstey

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Posted October 02 2014 - 06:55 AM

Actually, the opposite is true.

I think he meant at the maximum distance the image is sharper and this is true because as you said, lens aberrations are worse when the projector is as close as possible.  I tried my projector at closest distance but the CA was so bad I had to move it back to where it was more tolerable.

 

I can't remember how people think of whether it is max zoom or min zoom for closest position.  I guess it would be min zoom for widest possible image like how we think of a camera lens.







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