Screen throw

Discussion in 'Projectors, Screens & Video Processors' started by Wull, Aug 19, 2012.

  1. Wull

    Wull
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    Hi.

    Can anyone tell me what screen throw I should be using with my JVC350. My screen is 120" wide/49" high. I am using a prismasonic hd-5000r anamorphic lens.

    My room is 26ft long.

    Thanks...:)
     
  2. True Romance

    True Romance
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    Go to projectorpoint web site, they have a screen size/throw tool on there.
     
  3. Wull

    Wull
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  4. kbfern

    kbfern
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    I don't know how much difference the anamorphic lens makes but the projector central calculator has options for screen aspect ratio.
     
  5. Wull

    Wull
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    Cheers Keith.

    I recently moved my projector to a more exact central position in my room, and now I canot for the life of me produce a square image, the right hand side slops slightly. I am going to drop Prismasonic a line to see way they say.

    It's a nightmare of a lens to set up using the ceiling mounting bracket, I am now considering making a frame/box that the pJ can sit in/on attached to my ceiling, hence the throw question. At lease then I will have more control over the lens position.
     
  6. Peter Parker

    Peter Parker
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    You calculate the throw based on a 16:9 image. When using a lens, the longer the throw the better so as to reduce pincushion. Usually a rule of thumb is to try and have a throw of at least 2:1. For example, if the 16:9 portion of the 2.35 screen is around 90 inches wide, you want the pj lens at least 15 feet away (and the A lens mounts in front of that). Further is better provided you don't go beyond the pj being able to fill the screen height. You can experiment with the pj on the floor or coffee table before attaching anything to the ceiling so you know exactly what to expect for a given distance.

    If the image you have slops off to the bottom right, it sound like the pj is mounted slightly off centre to the left, with the pj swivelled to the right to get the image onto the screen. If you remove the A lens, does the image still slope?

    What I did for my A lens mount was cut a piece of MDF that had a protruding part that went over the front of the and the A lens would attach to that. You can then mount the ceiling bracket to the MDF. What you have to do is find the center of gravity with the A lens attached otherwise the weight of it will try and pull the pj down on the mount. To find the center, you can use your figers or a dowel under the j to find the balance points front to back and side to side (with the MDF and lens attached). Then you know where the centre point on the MDF is and can attached the mount there.

    I guess the thing with the box is that you can make it big enough so that you can move the pj to the left and right to get it completely square. With the ceiling mount, you'll have to unscrew it and screw it into a different place if the positioning isn't quite right. The box sounds far more flexible.

    Gary
     
  7. Wull

    Wull
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    Thanks Gary.

    My room is not square, so I used a laser level to check that the lens is central and square to the screen. Having just removed the lens I can confirm the picture is dead square.

    The problem with the Prismasonic's mount bracket is that there is little room for correction error, plus the lens is that heavy it almost's sags over the end.. http://www.prismasonic.com/pdf/mount_manual.pdf Awful design!!

    So for a '2:1' @ 16:9 = 98", I should be looking at 16.5ft?

    I have my PJ 20ft at present, I wander if it is to far away then?

    MDF could be an idea? :)
     
  8. Peter Parker

    Peter Parker
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    Is your 2.35 screen 120 inches wide? If so, isn't the 16:9 image around 90 inches wide?

    The 2:1 recommendation is a minimum, so being further back is better - 20ft is just fine. :)

    Gary
     
  9. Wull

    Wull
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    Ah, yes, may bad. I had zoomed out after taking the lens off :p

    Good to hear 20ft is OK, I may get away with a box behind the sofa then, not sure if I would in front :)

    So my next question Gary. My screen hardly has any boarder drop' 'low ceiling' in fact it is only 2". As it stands my PJ has a 7" ceiling bracket drop, do you think I could get a away with hardly any drop. meaning I would make the shelf just deep enough for the lens and PJ to sit.

    The Top of the screen would be in line with the PJ lens almost.
     
  10. Peter Parker

    Peter Parker
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    If closer to the ceiling works better, then I don't see why not. Just make sure there's plenty of air flow so the pj doesn't overheat.

    Gary
     
  11. Wull

    Wull
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    I hear what your saying. Cheers.
     
  12. Wull

    Wull
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    Prismasonic replied, they told me 5.5mtrs would be pretty optimum.

    So I have made the box, fixed in place. Now need a 90degree hdmi adaptor. I will also cut holes around the air intakes and exhaust. Also paint to create that WAF illusion that there really isn't a big letter box fixed to the ceiling!
     

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  13. Peter Parker

    Peter Parker
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    That was quick!

    It looks a lot easier to adjust the A lens as well.

    Gary
     
  14. Wull

    Wull
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    Thought best strike whilst the iron is hot Gary.

    It can't be any harder to set up than it was before, that ceiling mount bracket just does not make any sense, why make something that not only requires perfect balance between PJ and lens, didn't allow for easy lens alignment, just plan crazy!

    I may be able to shave an inch or two off the boxes height once up an running, but only if I feel this will not harm the PJ. Still, it's no bigger than my old Seleco 350 was :)
     
  15. Peter Parker

    Peter Parker
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    And it's probably a lot lighter too!

    You've just reminded me - I still have a Seleco 310 CRT that I doubt I'll ever use. I'll have to stick it in the classifieds some time.

    Gary
     
  16. Wull

    Wull
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    Now they where fun to set up, I could quite happily spend hours adjusting the convergence......all good fun!!?

    My old 350 is now used in a fitness club for the spinning class.
     

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