hello,

I recently finished up my new projector, has a 400 watt metal halice bulb, and 15.4" 1920x1200 lcd. I have a 330mm fresnel 6" from my bulb and a 330mm lens above the lcd, the fresnels and lcd are 1/2" apart. my design is a stand-up projector which is alot like an overhead with a triplet and mirror assemply that I took off of a dukane 680. here is another post where I put up some drawings of it:

http://www.lumenlab.com/forums/index.php?s...c=25770&hl=

this post is my fourth of 5 redesigns. the fifth just had some minor rewiring, the ballast is outside the case, there is no condenser or reflector, and the bulb is mounted on the back of the case not the side.

but my triplet is centered and 10" away from the pj.

I also cannot see the sides or the top of the image, like the whole image is not being focused, my top fresnel is an inch away from my lcd instead of 1/2" so i can have room for lcd circuit board.

I have theorized a couple of possabilities based upon what I have read on the forums:

1. my bulb should be futher away from the lcd, haven't tried doing this yet but will try it soon.

2. my fresnel between the bulb and lcd should probably be a 220mm, I put in a 330 as this is all I have at the moment.

what I have tried to fix it:

I tried taping off the edges around the lcd so light wouldn't leak through, this has helped a bit but I still can barely see the image, and I put a mirror below the lamp, this has not really helped at all.

also, it seems that I have to pull the pj really far away from the wall (like 20 ft) to get a focused image, even with the lens at it's lowest. I am thinking mabye the fresnel between the bulb and lcd is too close to lcd, then again, this shouldn't matter a whole lot, mabye I just need a 220mm. my triplet is a 330mm lens btw.

I will take pics of the image when i get a chance but believe me it is dim, out of focus (unless i pull it 20ft away from the wall which cuts off most of the image anyway), and for what i spent building is just plain horrible. so any advice would be appreciated.

Your lamp is too close to the rear fresnel and your triplet is too close to the front.

DJ

I agree about the lamp, but the lens is about 10 " from the top of the top fresnel, I tried raising the lens but it brings it even more out of focus. it seems that it may be too high. I really have to put up some pics of it. I will try switching out for a 220mm fresnel and moving the lamp down to 10" from the bottom fresnel. mabye this will help.

For the placement of the fresnels, the reason that the fresnels are there at all is just to direct the light so that it goes from the lamp, through the panel, and then to the triplet.

So in order to do that, the lenses need to work as a system, which "focuses" the lamp light into the triplet. You should actually be able to see an image of your lamp arc if you put a sheet of paper at the entrance to the triplet. If you cannot, then you are wasting light.

Only light that hits the triplet gets projected, no matter how much of it goes through the LCD. With no fresnels at all, you'll get an area of the LCD which is approximately the size of the projection lens (Actually a bit smaller) projected. This is because the rest of the light is going somewhere other than the lens, and is not being projected.

So, adjust the placement of your lamp and fresnels until you get as much light as possible hitting the triplet.

Some things to note: In a split setup, the further that the fresnel is from the LCD, the larger your projected image will be. This is because the fresnel acts as a magnifying lens. Also, because the fresnel isn't a particularly GOOD magnifying lens, this will also introduce distortion into your projected image. The greater the distance from LCD to fresnel, the greater the distortion. You need SOME distance in order to keep the projection lens from focusing on the fresnel grooves, but that should be as small as you can get away with.

alright, I have made some additional changes:

- I put the bulb at the very bottom of the case, and I added a condenser lens with FL of 220mm, (this has help with brightness a whole lot!!!)

- I moved my top fresnel closer to the lcd, this cured my focus issues.

- and I turned my bottom fresnel around, this helped alot with the brightness.

now, I can actually clearly see part of the image, enough to even watch some movies on it, however, I cannot see the full screen, because the edges of the screen are dark, as you can see in the pics below:







I have ordered a new 220MM fresnel, I hope replacing my bottom fresnel with that will help things. and just for quick specs, both fresnels are 330mm, the triplet is 330mm, and lcd is a 1920x1200 15.4" laptop lcd with controller. and you may notice a missing ballast inside the case, this is because I put the ballast outside the case and built in a port on the side just for plugging the ballast into.

any advice and getting this working better will be much appreciated.

hello, several more changes have been made:

1. I fixed that bowing that the bottom fresnel was doing (heat shield below it was in there too tight, was slightly too big, cut a bit off of it, now all is good.

2. switched out bottom fresnel for a 220 mm fresnel. helps drastically with light distribution.


however, the image is still not fully lit, more of it is lit if I remove my condenser lens. however, this makes the whole image too dark to make out if I put a program with a dark backdrop on it. and the lamp is a perfect 8 inches away from the fresnel. and the top fesenel is good otherwise I wouldn't be able to focus this thing. I will try going even lower with fl on the bottom fresnel, but overall, I am about ready to give up on this thing, it is too much headache trying to figure out wtf this thing doesn't want to cooperate.

You probably already know this, but just in case, the distances everything should be away from each other are, in order:

From lamp to bottom fresnel: 220m or 8.66 inches
Make distance in between fresnels and lcd as small as possible
From top fresnel to triplet: a few millimeters over the focal length of the top frensel, so like 340 mm or 13.286 inches
The triplet should have something like 50 mm travel or about 2 inches (and that should be further away from the fresnel to a max distance of like 390 mm)

Those are approximate distances, you still need to experiment some yourself. Dim corners are normally due to the lamp not being placed at the focal point of the collimator fresnel.

Hope that helps.