Question about Lumens output versus Zoom Lens position - Home Theater Forum and Systems - HomeTheaterShack.com

Old 04-28-11, 11:59 PM Thread Starter
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giboni

Join Date: Apr 2011
Location: brooklyn NYC
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Question about Lumens output versus Zoom Lens position

Hi everyone,
This is a great forum. Have learned so much in just a few days. Did try by searching to answer my own question.
Projector is BenQ SP890. It is literaly in the mail. About 5 days. The screen is coming together tomorrow.
2:35-1, 300 inch diagnol, 8feet 9inches by 276.00 inches 23 feet length. Table mounted projector. 15 foot ceiling. Screen
will hang probably 2 feet from top of ceiling. I have about 30 feet from the screen to the back of the space.
Tell me if I am wrong. After confusion and reading.Think I will get the maximum Lumen output of the projector at the widest setting of the Zoom Lens? Is this assumption correct? Figure after color etc. adjustments going to loose a lot of Lumens in that process. Ah obviously the Table height is adjustable even if I need a step ladder. Thanks in advance. Oh well. Just because it says 4000 does not mean thats what it does. Maybe I get a good refurb LOL !
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Old 04-29-11, 06:32 PM
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Re: Question about Lumens output versus Zoom Lens position

No zoom = maximum lumen output = longest mounting distance from screen..

Prof..
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Old 04-29-11, 07:49 PM
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Bob

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Re: Question about Lumens output versus Zoom Lens position

Quote:
Prof. wrote: View Post
No zoom = maximum lumen output = longest mounting distance from screen..
I'm a little confused by that statement. With "no zoom" do you mean the shortest focal length (widest angle) and if so wouldn't that be the shortest mounting distance from the screen? I assume you meant maximum zoom (longest focal length) which allows the greatest distance (all these assuming the same size image). Please clarify.
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Old 04-29-11, 08:21 PM
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Re: Question about Lumens output versus Zoom Lens position

Sorry for the confusion..

If you place your projector in a fixed position close to the screen, the smallest image you can obtain is when no zoom is applied..The image has to be zoomed out to obtain a larger image..

With no zoom applied, you would need to move the projector further back to get a larger image..

I hope that explains it more clearly..

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Old 04-29-11, 08:49 PM Thread Starter
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giboni

Join Date: Apr 2011
Location: brooklyn NYC
Posts: 19
Re: Question about Lumens output versus Zoom Lens position

Hi thank you everyone for taking the time to answer. Okay my unit is Manual Zoom, 1.20:1. I adjust it to no Zoom.
Then place it till it fills up the screen. This way the telephoto is not used which would cut down on Lumens.
Will be using an anamorph lens also. The closer the projector is to the screen the brighter the screen gets. Other
problems might crop up. Think I understand this now.
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Old 04-29-11, 09:46 PM
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Re: Question about Lumens output versus Zoom Lens position

When using an anamorphic lens you need to have the longest throw possible..to minimize the pincushion effect..
This means placing the projector as far back as possible..

Prof..
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Old 04-30-11, 01:53 AM Thread Starter
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giboni

Join Date: Apr 2011
Location: brooklyn NYC
Posts: 19
Re: Question about Lumens output versus Zoom Lens position

Okay. When everything is ready guess will learn the hard way ! In researching anamorphic lenses ostensibly
to find a cheap one. Read this from the manufacturers web site." The projected image can then be zoomed in or out to allow for the corners to “overscan” on to the blackout material". {Pincushion}
With a little luck after color adjustment and maintaining a dark space this projector just might do it on this size screen. Am going to replace the bulbs in the fire exits to very low wattage. Paint part of the ceiling in front of the projector
flat black. Installation is certainly a compromise of many factors. Thanks again for your input and time.
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Old 04-30-11, 06:26 PM
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Re: Question about Lumens output versus Zoom Lens position

Quote:
giboni wrote: View Post
" The projected image can then be zoomed in or out to allow for the corners to “overscan” on to the blackout material". {Pincushion}
Yes..that is correct..It's almost impossible to get your projector in the exact position where you have the right amount of overscan (with zero zoom) to have the pincushion distortion on the borders, so it's best to get the image almost to the edges of the screen with your mounting position and then apply a little zoom to give you the right amount of overscan..

Prof..
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Old 04-30-11, 06:49 PM Thread Starter
Shackster
giboni

Join Date: Apr 2011
Location: brooklyn NYC
Posts: 19
Re: Question about Lumens output versus Zoom Lens position

Hi,
Thanks again for your time and input. Definitely will remember that. Hopefully you are still on the forum ! Have another question.
Based upon a 16 foot ceiling the aforementioned screen dimensions. The screen sitting off the floor approx. [5] 4 feet 4 inches how tall will the table that the BenQ SP890 sits on have to be ? I am going to use an old heavy adjustable steel mount. Originally for an 18 inch Sub-woofer. It can hold a heavy speaker up to six feet off the floor. Figure might be a formula for this.

Last edited by giboni; 04-30-11 at 07:56 PM.
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Old 04-30-11, 06:58 PM
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Re: Question about Lumens output versus Zoom Lens position

Quote:
giboni wrote: View Post
The screen sitting off the floor approx. 5 feet 4 inches
Why so high off the floor!? You'll get a crinked neck that high up!!
Ideally your eye level should at about a third of the way up from the bottom of the screen..

I should add that at my suggested position, you will get more of an immersive feeling..

Prof..
Home Theatre...the never ending story!

www.dogboardingsa.com
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