| dizzknee |
I'm just starting on my DIY OHP project. I'm basically following this sites directions:
http://www6.tomshardware.com/howto/20041113/index.html
My main concern is throw distance. I want to get a screen size of about 52" by 92". What would be the throw distance for that? Also the LCD panel I'm looking to buy is either the:
Micron AP150T 15" OR
NEC LCD1545V 15" OR
LIQUID VIDEO E15LCD1 15"
I have already bought the Apollo 2250 Concept Portable Projector.
Specs for that are here: http://www.touchboards.com/apollo/2250.asp
Any thoughts or advice concerning the throw distance issue as well as the equipment I've bought and am looking to buy.
Thanks a bunch! :)
Earle |
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| Guy Grotke |
The 15" monitor will have a 3:4 size ratio, so your image will be 52" high and 69.3" wide. (That assumes that those numbers you mentioned were the maximum size available in both dimensions.) This would be an 86.7" diagonal image.
So your magnification would be 86.7 / 15 = 5.78
None of the literature you referenced lists a focal length for the OHP lens, but most of them are around 325 mm.
Throw distance = (M + 1) * FL
So 2202.8 mm (or 86.7 inches) would be your throw distance. But that assumes I guessed the focal length correctly. |
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| Guy Grotke |
Of course, with a 10.5 by 10.5 inch stage on the OHP, 1.5" of the sides of your LCD will be cut off!
A 15" LCD is 9" by 12". The standard ratio between vertical and horizontal is 3:4, so the math is easy: If the sides are 3 by 4, then the diagonal is 5. Given any dimension, you can quickly determine the other two. For example, a 15" LCD is just 3 times the basic 3:4:5 ratio. |
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| dizzknee |
| quote: | Originally posted by Guy Grotke
Of course, with a 10.5 by 10.5 inch stage on the OHP, 1.5" of the sides of your LCD will be cut off!
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Guy Grotke:
I'm a little confused now. Are you saying that the OHP that I bought is not a good candidate for this project? Is the stage size (10.5 X 10.5) too small? |
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| ppmz |
sqrt ((10.5^2) * 2) = 14.85"
It's just a little bit smaller than a 15" LCD. I guess you can shrink the image a little, but it all depends how you plan to drive the LCD (with a PC?). |
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| dizzknee |
| quote: | Originally posted by ppmz
sqrt ((10.5^2) * 2) = 14.85"
It's just a little bit smaller than a 15" LCD. I guess you can shrink the image a little, but it all depends how you plan to drive the LCD (with a PC?). |
Yes, I'll be driving it with a PC using a RealMagic Xcard, most likely. |
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| dizzknee |
If I'm using a PC to run my DVDs, along with the RealMagic Xcard, can I simply use something like dscaler or Powerstrip to resize my image slightly?
Any issues with this solution?
Thanks :) |
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| Guy Grotke |
sqrt ((10.5^2) * 2) = 14.85" doesn't really apply here, since it includes unused area in the vertical dimension.
A 15" diagonal LCD has an active pixel area of 9" by 12". Since your stage is only 10.5 inches wide, 1.5 inches of active area will not be illuminated on one side. The lens will project it, but it will be dark.
SInce you are using a 1024 by 768 pixel LCD, you will lose 128 pixels from your horizontal resolution. You can make up for that by shrinking the whole image with a software solution. Or you could modify the OHP to hold larger fresnels. Those would cost you about $50. |
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| wylie-c |
| Powerstrip should work like a charm, I'm using it on my setup. 15" Viewsonic on an OHP, with Powerstrip to get around my ffc issues. I keep it so everything is projected in a 16:9 aspect ratio, so it fits on my screen. |
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| dizzknee |
| For my 10.5" X 10.5" stage, wouldn't a 14" LCD panel be a little better suited than a 15"? Are there any definite advantages working with a 15" over a 14"? |
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| wylie-c |
| A 14 would be ideal, it's just that they're harder to find. And I'm not sure if the response and contrast would be up to the same level as a newer 15". Most 14's are older. |
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| Guy Grotke |
14 / 5 * 4 = 11.2 inches wide
Still a bit too big for a 10.5" by 10.5" stage OHP. (A 13" LCD would be perfect.) But all the 14" LCDs have response times around 50 msec, and low contrast ratios. Most 15" LCDs have response times under 30 msec, and contrast ratios above 300:1, just because they are a later generation of technology from the 14" panels. 17" LCDs are even better: 1280 by 1024 with response times under 25 msec and contrast ratios upwards of 450:1!
Even with those problems, 14" LCD monitors are quite a bit better than all but the very top end of the OHP projection panels. |
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