Well techniclally this isn't keystone correction, more like idea's to project at an angle to get the projector out of your viewing area.

Heres what I was talking about when I talked about optically shrinking the size of the lcd, then using that to project at an angle.

This would require a "special triplet" that would project a 7 inch image. This would be tricky because you'd have to use a lot of fresnels to keep the light where you want it, as you can see, this uses two lens kits.

Idea 2!

I'm sure this idea doesn't work, as I'm sure someones tried it before. But what the heck.

In this you place the triplet off centered from the collectors focal point, so all the light is pointed above the center of the lens. This might result in an angled projection.

Smaller projection size would probaly allow you to off set the lens even more.

This might also require you to tilt the triplet back or forward a bit (its kind of hard to explain why I think you might)

So anyone who has a lumenlab projector could try this idea, (don't have mine yet)

Just off center the lens a little bit and see what happens. Try doing it with a smaller projection size, about 6 to 8 feet.

The ONLY way to adjust keystoning with the standard design is by tilting the fresnel. Moving the triplet lens simply dims the picture. Tilting the screen, LCD and/or the triplet will focus the picture (or defocus - depending on your perspective) in the direction of the tilt.

Theory 3 is sort of a mix of the first 2.

A triplet that focuses an image very very close and reduces the size by half, before it goes to the projection triplet which is offset.

hmmm maybe so. Just idea's. But remember this isn't keystone correction, its just theories to allow you to off set the projector, the lens is still perpendicular to the screen.

Besides this isn't the standard design I'm using at all.

Anyway, I'm sure there the people at lumenlab who know 100 times more about optics could figure out a better way, but would they want to? Maybe research isn't being done for better keystone correction/off set projection anymore. Maybe they are satisfied with the quality of 15 degree keystoning. Or are occupied with something else right now. Maybe they know of an expensive solution but figures no one would bother to use it.

Its a matter of preferance, me I'd be willing to spend a lot more money to get the projector out of the line of viewing. I'd also be willing to make my projector a lot larger.

So maybe some of these idea's work but they haven't been brought to light because they aren't very practical.

Heres another theory.

I've discovered that when you project a straight image onto an angled surface, and place a lens in the path of the projection parrallell to the screen, it corrects the projection. As shown in the top diagram below. However my experiments did not use high quality lenses and there may have been distortions I didn't notice, but lets just assume there weren't. This is actually similar to tilting the collector fresnel if you think about it only you are using a lens instead. This seems like a better idea to me because fresnels are not great for changing the size of the image, they are only ok for bending light. The reason keystone correction works is because the fresnel makes the top of the image larger and the bottom smaller, which will be reversed after it passes through the triplet. So maybe tilting one or more of the lenses in the triplet will work the same was as tilting the collector. NOTE! You could only tilt the midle and back lens of the triplet, the front lens would have to be parralell to and centered on the lcd according to my theory.

Diagram 2 shows the triplet with lens b and c tilted back slightly, however there are many combinations you could try. Tilting only lens b, tilting only lens c, tilting lens b and then tilting lens c a little more then lens b, there are lots of combinations.

I don't know how hard it is to dissasemble a triplet, but I know one guy here who got a faulty triplet and dissambled it to try rearranging the lenses, so I guess it must be doable.

If titling the lenses inside the triplet doesn't work, then maybe some type of lens placed in front or behind the triplet and titled will do it.

Again, I think a smaller projection will allow greater angled projection then a larger one.

Maybe I should post this stuff in the mad scientist forum.

What about using flexible reflectors curved in 1 dimension (cylinder arcs)? I'd imagine that if you could get reflectors that didn't totally screw your image, you could get effective keystone adjustment from that.

Image: Projector is 3 feet from a wall, projecting upward @ a tilt onto a very slightly concave cylindrical mirror (vertical). The beam then goes back over the projector at the opposite wall. Since the bottom edge of the beam hits a shorter angular curvature, it isn't compressed very much. The upper edge of the beam hits a larger angular curvature and is compressed more. For this to be conveniant, you'd need a relatively low-angle beam, of course.

That might work . But getting a mirror to the exact curvature wouldn't be a bit easy. A larger mirror would be easier though. Maybe bulding a frame for it.

What about using the 1/8" acrylic mirrors that are being used for Light Fusion? One could get a small one + experiment with framing/mounting options. How one could consistantly apply the pressure, I know not.

I suspect, though, that you would be forced to use steel throughout, and keep the mirror at more than a slight bend. I think clamping it from both sides is going to be the only way to equalize the pressure so that it won't distort vertically. Then, the clamps could be mounted to vertical tubing and it could be contracted via adjustment of threaded rods at top/bottom.

Anyone up to try this? Or have more ideas about the optical theory that could produce good keystoning like this?

Also, I know a lot of you have fresnel-adjustable keystone built into your PJs.

What are the downsides of having it enabled vs having it disabled? I would imagine increased blurriness proportional to distance from the LCD, and decreased light output proportional to angle the fresnel is at relative to the LCD.

Good idea's, it just might not be easy to get the correct angle, experimenting would be good.

I like the idea though.

Someone needs to try my triplet tilting idea.

Actually, using a collector or collination fresnel and putting it in front of the tripet off cented, might work the same way as the mirror.

On second thought it probably wouldn't, you need something to bend the light, not just redirect it.

Maybe something more like this. A fresnel that is just a bunch triangles, instead of bending the light, it just shoots it out sideways. But I think how well this works would depend on how small the triangles are, and they may need to be super small.

Hmmmm..it would probably need to be one triangle per pixel, so you'd need 768 triangles in a 9 inch tall fresnel. It could be easier if the fresnel was bigger.

(edit) Wait, that probably wouldn't work, because the fresnel is still centered on the middle of the screen. PHOEY! :angry:

Maybe you could try using one of those convex mirrors you see in supermarkets, those are easy to get.

Fresnel fabrication... not gonna happen

Concave mirrors... After examining one when I saw your thread, they're very very rough - you have regions that compress and regions that don't. Anything over a few inches away looks terrible because of nonuniform magnification.

I just found out that some of the newer overhead projectors have optical keystone correction. I'm sure we can get a hold of one or at least observe how it is done and duplicate it. The one I read about had keystone correction up to 13 degree's, which isn't really much, but there might be better.

Can you use a laptop lcd screen in this type of configuration?

I wish I had more optics knowledge. It seems that this is the area that all the vast improvements will be made in DIY projectors. I am lucky enough to go to one of the four engineering schools in the US that has an opical engineering. And I have one friend that is about to graduate in optics. I have talked to him about some of these lenses and such, and the only problem is the application we are using these optics for are a little different from his textbook optics but I will show him your ideas and see what he says.

Thanks man!

Heres a website I found called info opctics or something like that. Heres a quote:

"Keystone distortion that occurs in overhead projectors when the projecting lens head is tilted upward to a high screen is commonly observed. Here we suggest a modification of the typical overhead projector to eliminate this distortion of the image. © 2004 Optical Society of America"

It says "Download pfd document" below, but you need to be a subscriber to download it.

(edit) Heres the link:

http://www.opticsinfobase.org/abstract.cfm?id=80577

It seems like much of what you describe is "lens shift" which is common in most higher end projectors and is now making its way to entry level units. You might want to take a look around at projectorcentral.com or follow these links..

http://www.hometheaterpeople.com/tutorials/lens-shift.asp

http://www.projectorcentral.com/anyplace_projection.htm

Right! Lens shift! Looks like a lot of projectors now have lens shift capability. Time for brain to develop a triplet with lens shift capability.

BRAIN!!!

I'm pretty content with just tilting my fresnal. Maybe you should give it a try. It works well if you also align your triplet with it.

You forget that when you run your image through all those optics, your just dimming the image more and more.

Didn't forget. I know it will.

Tilting the triplet to align it with the fresnel?! Thats the same as just tilting the lcd! Thought that didn't work. Obviously you can't simply tilt the lcd or the back lighting will be messed up, but still thats pretty much the same thing.

It works indeed. Though my system is only doing 7° Keystone adjustment. I have my screen angled at around 7° also to make up for the difference.

Well is there absolutely no distortion?

I would love to see a close up picture of a projected image without keystone correction, and a close up picture with 15 degree keystone correction, so I could really see the differance.

I won't get any where near 15°.

If you need 15° Keystone, then maybe you do need an alternate solution.

(sigh)

I have designed my PJ to allow me to tilt the LCD up to 10 degrees, the front fresnal up to 20 degrees and the triplet up to 10 degrees. I did this because I want to hang my PJ on the ceiling (only about 7.5 feet high) and project a 4 foot high image. I calculated a needed about a 20 degree keystone to place the screen in the middle of the wall, so the PJ would not block my view. One of the things I was worried about was wether the LCD would become too dimm is tilted. Some LCDs become dim, and some do not.

Still building but I did perform an optics check with the LCD in. The cmv 529A provides no image degredation when tilted up to 10 degrees. This was something I was worried about. I did not see a different in brightness with the LCD tilted or upright.

Unfortunately no pictures because I do not have a digital camera.

FYI

Today I used a slide projector triplet and tried taking out and off setting the lenses from eachother, like the picture below shows, I found it worked to a certain degree and didn't appear to distort the image, however the lenses had plastic frames around them so when I off set them the plastic edges blocked most of the image, so its difficult for me to be 100% sure. But anyway, it seems to me that the distance between the center of the lenses have to always be the same, so the hinging apparatus I drew below should work if thats true. But again I'm not positive.

I'm going to continue experimenting, and see if I can get the plastic frames off the lenses, but untill then I thought I'd post it here to see if you or anyone here can do it with a lumenlab projector. Of course it only works to a certain degree, and I think smaller projeciton size will allow more extreme off setting.

Cheers!

This idea seems to have merit, I'd like to see where this goes.

PM sent

Ok, I managed to get the plastic pieces off the lenses by sawing them off by hand, lol, that was a nightmare, but now since I don't have the case for it I have to adjust all three lenses manually to find the image, which isn't easy. Anyway I'm trying build some sort of apperatus like the one I showed. When off setting the lenses they need to be slightly readjusted to bring the image into focus, like I said, I think the distance between the centers of the lenses needs to always remain the same, or maybe they need to be manually adjusted for every situation, not sure. Anyway like I said I'm having trouble getting the image into focus even when projecting straight on since I'm just feeling for the image by moving the lenses by hand. So its hard for me to tell if this is working 100% yet. But even if I was I don't know how well it will work with a lumenlab projector.

my feeling is that if 12 feet is the maximum projection size, then you should be able to get a 6 foot image centering the projector on the top edge of the image, and an 8 foot image 1/3 below the top of the image, a 10 foot image 5/6 below the top of the image, and so on.

Maybe if this works brain might be interested in modifying the triplet specifically for this purpose. Or making a new one. I'd think the middle and right lens would need to be improved slightly but the first can be left alone.

Guess I shouldn't get my hopes up.

Ok. just got done some experimenting. I feel that I can now safely say that the idea works, shifting the lenses and adjusting the lenses correctly does produce an angled projection with a clear image.

Now its just a question of how much the lumenlab triplet can be shifted. Like I said, when the lenses are shifted sideways the distance between them appearantly needs to be adjusted slightly, whether or not they just need to have the same distance apart from center to center I'm still not sure but its my best guess.

All ceiling mount projectors on the market uses keystone ?

Every commercial projector I've seen offers keystone correction.

Then just copy the design

Lol, well most use digital keystone correction. So that we can't copy. Lens shift is something I think we can copy though.

Hmm...from what I'm seeing, off setting the lens I'm using is causing a lot of leaked light, while it can be brought into focus, a lot of light is wasted. If the lumenlab projector uses all the available space inside the middle and right lens, then it won't work, but if theres some room to move, it should work.

Of course if the middle and right lens were larger, it would work much better.

The solution sounds pretty simple to me if you want keystone correction and every commerical projector offers keystone correction. Then by a commercial projector!!!

DIY is limited to the skills that you as in yourself have. Commercial products are limitted to the resourse that a commercial company has. I can't make a car from scratch so I buy it, there are plenty of very good comercial projectors out there and the prices are dropping, I nwish you luck in your purchase.

(cough)

That was always an option. But the bulb price for a commercial projector is ridiculous.

You keep complaining about keystone. Nobody else seems to have a problem. If you really need keystone get a commercial unit if you can't afford one, then you will have to live within the limitations of your skills and commonly available products. Its often easier to move the projector than try put the projector in a location not inline with the screen. What is your projector location versus the screen, what angles to you have to content with maybe there is another solution. I'm going to place my projector in a location that projects on a side wall because there wasn't a configuration for the wall that I could get to work (would need a 800mm FL) but thats the best I can do. I would have prefered to have it on the front wall but it won't work so I live with what works. Engineering has been described as: making what you want out of what you have.

If your not part of the solution you maybe part of the problem.

Think things through and find a solution rather than complaining that others haven't solved your problem.

Mikau,

Keep up the good work. I sincerely hope you figure out a DIY way to lens shift whether Pagercam wants you to or not. If I come across anything that may be of help I will be sure to post.

Chris

I don't think Pagercam is criticizing the work Mikau is trying to do, but the point he's trying to make is a good one.

The existing method for keystone correction works fine, and can even be utilized with extreme angles if you're willing to adjust focus using tilted triplets and/or screens.

Mikau is trying to overcome a limitation of the design of the entire optic system (the fact that the PJ must be at a 1:1 distance from the screen) in a way that's really not going to be physically possible without significant loss of brightness.

Personally, if I were in Mikau's shoes, I'd spring for the pro lens kit, place my projector as far back and as centered as possible, and not have to worry too much about extreme keystone correction. But that's just me...

Read like criticism of his thinking, intention and pretty much everything about what Mikau is attempting to do. Why else would he tell him to buy commericial if he needs keystone, that he may be part of the problem and that he needs to think things through. Yeah, reads like crapping on someone's parade to me- for what purpose exactly I don't know (to be the sage to an obviously befuddled fellow?)?

I disagree that it is a good point, especially when, if you actually read what Mikau is trying to accomplish, it is in fact lens shift and NOT keystone correction. So what if he called it keystone correction but then described lens shift? He is thinking and trying to accomplish something without telling others what they should do. If he's tilting at windmills I guess he'll find out and then you can all say so. But until he gives up, and I hope he doesn't because I for one wouldn't mind seeing a DIY method for lens shift, I'll help if I can.

Good luck Mikau.

Thank you!


It doesn't bother me so much, all I hear is "SHUT UP EDISON! The candle works fine!"

Anyway, I also had some luck last night tilting the front lens (the last lens the light goes through before leaving the projector) that worked to some extent for keystone correction, though the lenses for the triplet I'm using are pretty close together and you can't tilt it too much without pulling it away from the other lenses which destroys the focus.

I've come to the conclusion that the solution to off set projection, whether it be keystone correction or lens shifting, needs to be in the triplet. So if it doesn't work with a lumenlab triplet, then it will only work if brain wants to develop a lens shift triplet.

out of curiosity what is the farthest distance someone has put the pro lens back and still gotten a good picture? how far is recomended?

Don't know much about the pro lens.

I am not looking for a longer thow distance if anyone thinks I am. I'm looking for better keystone correction or a lens shift system. My experminents have shown it does work to a certain degree, now it just needs to be tested on a lumenlab projector.

Wonder what brain has to say about this.

Longer throw distance = smaller angle = less keystone correction required.

Unless you want to get right in front of the screen.

Longer throw distance would also make it MUCH easier to deal with picture correction, since you're not dealing with a beam that wants to expand as much and kill your lense arrangement.

True. But I'm talking about lens shifting or optical keystone correction within the triplet. I've got it to work quite well with my experiments, I just don't know if it will work with a lumenlab projector.

Keystone correction for the lumenlab projector still requires you tilt the collector fresnel. This causes distortion, whether its a little or a lot. I'm looking for a solution that causes no distortion, great or small.