Ace - is there a good place to read how the lens shift affects the setup of the internals? I've seen you mention the offset fresnel but I'm not sure how each would be offset.
Thanks!
Thanks!
Ive got an optical book here bud that helped me out on the matter, an offset frensel will work but will give you a keystone issue so you are going to have to use 2 off set prisims, (atleast thats what the pro's use).
All of the guts stays the same, all you have to do is get 2 wedge prisims and rotate them right behind the projection lens 😉.
Trev🙂
All of the guts stays the same, all you have to do is get 2 wedge prisims and rotate them right behind the projection lens 😉.
Trev🙂
They are cheap for the small ones (depending on grade), i need 60mm+ sized ones that run into $150+ for each one and you need 2 of them, and they are the cheap ones!!! lol.
You want a high grade to minimise the losses aswell, and i think from memory they have to be run on a paralelle projector system or they wont work (have to look that up, and converting our projector system to a paralle manner isnt hard).
Trev🙂
You want a high grade to minimise the losses aswell, and i think from memory they have to be run on a paralelle projector system or they wont work (have to look that up, and converting our projector system to a paralle manner isnt hard).
Trev🙂
Nice work. So you are sitting at 12 feet watching a 10 foot wide image? Are you seeing pixels or screen door effect? How is the viewing experience?
I thought 1.5 x image diagnol is the max recomended for viewing distance.
Will tilting the projection screen work just as well?
I thought 1.5 x image diagnol is the max recomended for viewing distance.
Will tilting the projection screen work just as well?
I find that I am just unable to make out the individual pixels when my eye is exactly as far back as the projection lens (lumenlab triplet). Right now I have it set up behind the couch so I'm about 9 feet away from a floor-to-ceiling image, it's all right especially for widescreen movies. However I'm designing a new floor-mounted enclosure that doubles as a coffee table and HTPC box.
Do I have my math wrong then?
At 9 foot throw you are getting a 10 foot wide image with a 15 inch diagonal lcd and 13 inch standard triplet?
At 9 foot throw you are getting a 10 foot wide image with a 15 inch diagonal lcd and 13 inch standard triplet?
I said I'M 9 feet away. I'm on the couch. The couch is in front of the projector. So the throw is about 10 feet, and the image is about 11 feet wide, 160" diagonal. I think it's OK but still too close, so my new setup will have the projector several feet in front of the couch.
Thats what I want to do also. So the lens will be about 8 inches off the ground correct?
How much of a tilt up do you think would be required and keystone correction with the top fresnel? So if you tilt up projector does the top fresnel tilt top forward or top backwards?
The lens will have to be a bit higher than 8 inches, according to my Autocad drawings so far, about 12 inches when tilted 14 degrees. That's about the limit for keystone adjustment with a front fresnel.
You have to angle the fresnel to parallel the plane of the projection surface.
You have to angle the fresnel to parallel the plane of the projection surface.
fresnel spacing and keystoning
I've been playing with my projector trying to resolve the keystone issue. I saw the image you posted, and it looks like you have a decent picure. In order to correct my keystone, I need an angle of about 12 degrees on the last fresnel. This solves it, but, this also provides much unwanted blurring of the image on the top and bottom. If I square up the fresnel, it's vey sharp.
I think I may also have too much space betweent the fresnels and the LCD. I don't think the spacing on the rear fresnel is too critical, but I find increasing the spacing on the front fresnel caused an increased image size.
From your experience, what is the spacing of your fresnels? What is the keystone angle with the front fresnel?
I notice you use a norpro for a reflector. Would you mind posting the size of the norpro so that I have a referance to find a suitable reflector. I've managed to get the lighting even accross the image, but I'm hoping to improve the luminisity.
I've been playing with my projector trying to resolve the keystone issue. I saw the image you posted, and it looks like you have a decent picure. In order to correct my keystone, I need an angle of about 12 degrees on the last fresnel. This solves it, but, this also provides much unwanted blurring of the image on the top and bottom. If I square up the fresnel, it's vey sharp.
I think I may also have too much space betweent the fresnels and the LCD. I don't think the spacing on the rear fresnel is too critical, but I find increasing the spacing on the front fresnel caused an increased image size.
From your experience, what is the spacing of your fresnels? What is the keystone angle with the front fresnel?
I notice you use a norpro for a reflector. Would you mind posting the size of the norpro so that I have a referance to find a suitable reflector. I've managed to get the lighting even accross the image, but I'm hoping to improve the luminisity.
ace3000_1 said:
What exactly is a parallel projector system? Searching very quickly i think it has to do with the light source being at infinity.
Would it be possible to use 25mm wedge prisims? since the field fresnel is condensing the light if we put the wedge prisims near the focal point of the fresnel, it should catch all the light.
My guess is no, but you can always hope.
A parallel projector system is a projector that doesnt need to be tilted towards the center of the projection screen when it hangs of a ceiling in a perfect horizontal position. The prims in it bend the image correctly as if it was being tilted towards the center of the screen.
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