Click to view attachmentClick to view attachmenthey, i am attempting to do a semi-permanent vertical pj with the pro lens. can anyone tell me what the minimum fs mirror surface area can be? here are the details: my pj housing will be 33" high, and tapering to a 6" wide point at the top, where my lens is placed now for a horizontal build. i am going to mount the box on the adjustable bases of a few of my monitors, so i can raise the box to switch light engines. think of it as sort of a suspension system for my pj. i wrecked the larger fs mirror from my dukane 682. the top mirror used to reflect the triplet is 3.75" tapering down from 4.8725". i realize this is smaller than the aperture of the pro lens. however, i was thinking i could put it at the very top of the box, and the triplet would be mounted as high as it could go. just an idea.

if this dubious setup won't work, where can i get a carbide cutter suitable for use on the LL FS mirror? i have 2 weeks before i move to chicago, and i am FREAKING OUT that won't get this done. anyway, any advice or tips that you guys have would be greatly appreciated. i am including a diagram of how my basic design will look.

What I usually do to figure this out is draw a scale drawing of the straight light path then draw the mirror at 45 degrees across the light path then measure the length of the mirror needed to capture everything. I think that it will have to be larger than the triplet because it is at an angle so it will have to be longer. I hope I am making sense. Really it will depend on the size of your panel and the focal lengths of the lenses. You are using the 650mm fresnel? What are the dimensions of your panel? What is your expected throw distance? Are you going with split or unsplit? If you can answer those I can give you a better idea of the size mirror you will need.

There was a thread somewhere about cutting the FS mirror from Lumenlab. It was said to use a regular glass cutter. Try to find the thread if you can. I can't remember all the advice that was given.

Hope this helps.
David.

ehhh i caved quickly and bought an fs mirror from anchor. 6.5"x9.45" should do it, as i am pretty much placing it where the pro lens is now in my pj. yes i am using the pro kit, and a 17" 4:3 dell 1706fpv. i have not fully decided on unsplit. i will give aligning them one more try, because it would probably be best for a longer throw than what i have now using the split. my throw distance is basically as far back as i can go using a 10 foot diag dalite and 4x8 foot matted plastex/mmud screen for widescreen stuff. my apartment is roughly 25-30feet long. the room in which i plan on setting up is actually really cool for a theater room. it has curved walls like this (__) which i think aids in sound refraction. it's been a while since i took audio and acoustics.

Ok, here is what I came up with. I consider this to be pretty rough and would have to be checked in actual use. I am making one guess that I am sure is wrong. I drew this out with the image of the LCD coming to a point in the center of the triplet.

If you were lust trying to capture the image of the LCD then I come up with a 2X3 inch mirror. In practice this would be larger because I think the image of the LCD does not come to a point in the center of the lens.

However you also want to capture the light being bent by the fresnel which has a longer focal length than the triplet. In a split fresnel setup I figure the mirror size would be about 4X6. In unsplit it could be a little smaller.

With the image size you mentioned I come up with about 12 feet from triplet to projected image. You can double check that in focalcalc.

I think for a throw near this size you might want to go with unsplit optics. The way I drew it out it looks like you might miss some of the light if you run split fresnels.

Also I figured this by placing the lens until it was just out of the lightpath. That means that you can not move the triplet closer for focusing, only farther away. This would limit your projector to screen distance to 12 feet or less.

The center of the mirror would be about 19.5 inches from the LCD and the middle of the triplet would be about 3 inches from the mirror.

Again, these numbers are for split. For unsplit the light cone would be smaller allowing you to move the mirror forward a little and allowing use of a slightly smaller mirror.

Hopefully my reasoning is close to correct. I drew the focus of the fresnel as a point in the height of the panel and to about 3 inches in the width of the panel because the light is not focused to a point, it is focused to a magnified image of the arc tube of the bulb. This also assumes that the bulb will be horizontal across the panel.

If you like, when I have time I will draw a nicer drawing and scan it and post it. It might not be for a few days though since I am in the middle of doing a lot of paperwork at home.

Hope this helps.

David.

Edit: By the way. From your description it seems the room you have for your theater is great. Good luck with it.

Wouldn't this be the same as the OHP that have a lens with a mirror above? So the minimum size would be the triplet width (plus a little to be sure) for the width and 1.5 * width for the height to allow for the image stretch at 45 degrees which would be Square root of 2 (1.414) so round upto 1.5. So using the standard triplet the minimum mirror should be something like 80x120mm.

Maybe but he is using the pro triplet. Doesn't the OHP have the mirror after the triplet? He wanted to put his before. Anyway, I was just trying to answer his question of what the smallest mirror he could use would be.

David.

Isn't the mirror on an OHP a lot closer to the triplet than 3 inches? You might not be able to do that since the triplet might interfere with the light path. Now I am concerned because I came up with basically the same answer you did if you change your calculations to the pro triplet. I think it should actually be a little larger.
Or does the pro triplet not protrude inside the box allowing you to place the triplet right up against the mirror?

If it is the pro then 100mm x 150mm. The smallest mirror would be the point closest to the triplet, before or after would still be based on the size of the triplet.

Ok, I thought that if the mirror was right at the triplet then part of the triplet might be in the light path. I guess I was wrong. So I came up with the same answer just went about it the wrong way.

David.

Okay this might solve a problem before it occurs. I decide to make a vertical pj with th efs mirror before the lense. My fs mirror is about an inch away from the regular triplet lense about 4"x6" in size. The original ohp fresnel was 330 compared to the lumenlab 320 fresnel so what ended up happening was me projecting a clear image on the screen but slightly light in the corners. When I looked up at the ceiling I saw what appeared to be light images so it convinced me that I wasn't capturing all the light into the fs mirror even though everything showed up on the screen. You might not be able to go with the triangular top you were best to keep it as squared as so that you don't loose any of your image.The fs mirror from the ohp was all that I had so until I can order a larger one I'm stuck maybe at least 8"x10" thats the size I will go for when I order the mirror for my pro lense.

That sounds like good advice. At least put everything together somehow before making any permanent cuts to see if it will work out the way you plan.

David.

the triangle top is actually the way my projector works now. darkmeat, i don't doubt your experiences, but maybe that was just ambient light from the throw of your front fresnel? by that i mean there may have been light spillage, as there is in my system. i am hoping to remedy this problem during the "oh well i already took it apart, might as well improve it" stage of rebuilding.

but the triangle is perfectly fine for projecting; the very purpose of our collimator is to focus the image into a size usable by the triplet. to those ends, no usable light/image should be anywhere other than in the triplet's aperture, i.e to a 100mm or less sized image. therefore, the design, which is not mine sadly, is ideal.

in any event, the mirror at 45 degrees is effectively intercepting the beam of light and bending it at a right angle. obviously, right? the new mirror i got, which is 6" wide, is adequately suited to capture this beam at a distance of roughly 2 inches mean, from where the beam is now being projected in my unaltered horizontal pj. it's a goofy octagonal one from anchor optical, but i tested it yesterday on the stand i made for it, and it seemed to capture everything fairly well. i was only able to project through the pro lens about 2 feet away, on to the ceiling. but it looked like everything was there, present and accounted for.

darkmeat, as far as your projector is concerned, since you are using a shorter throw collimator, the light cone is going to be shorter, obviously, and relatively wider than the longer throw of the 650mm i am using. in which case you may need a larger fs mirror. i guess i am not telling you anything you don't already know. but, the same formula could be used to find the size of the light cone at the point where you and i want to bend our projection and put it through the triplet

does anyone know of a formula to determine the exact circumference of the beam at any given point? is it just a simple geometry equation? my high school math is predictable rusty after 13 years. life or death, or even mundane situations don't present themselves to me where geometry could help.

You could just draw a picture to scale if you don't feel like doing trig and geometry.


Draw a horizontal line to represent the diagonal of your panel. Draw a vertical line to represent the distance from the panel to the triplet. Draw a second horizontal line to represent your triplet.
Draw a couple lines from the edge of the panel to the edge of the triplet.

Where ever you place the mirror needs to be able to fully intersect this triangle. Make sure you draw everything to scale tho.

thanks, dude. k.i.s.s., right? don't know why i didn't think of that, i am right brained so arty stuff is my bread and butter. lately though, i am no-brained. so thanks.

Seems as though you are getting there with your design ideas I'm tempted to just switch to the long throw but I'll stick with my present setup for now. I do have some light spillage in my pj but the main prob is the size of the fs mirror working with the light cone that I have its just a bit small so I plan to just order the larger fs lense from lumenlab and make it closer to joe's vertical design. I hope you solve your problem though since I will more than likely have the same issues when I do switch to the long throw.

One thing iv noticed from some threads is that many are having problems focussing with the pro lens.The problem seems to be when there is too great a distance between the mirror and field freznel.Many have got good focus at about 7 and a half inches or less - which is very close ,and relied on the triplet extending out of the box.

Obviously you need a big mirror to catch the light as well as keeping the box square at the top.I think the pro will work at other distances but if youve paid good money for the lens you want to make the most of it and have good focus.Personally id keep the mirror close to your field freznel (split) or lcd (unsplit) to make things easier but if you want to give it a go the other way hope it works out for ya..

I'd like to revisit this topic, if possible. I'm trying to retrofit an OHP's triplet and mirror (4" x 6") in a similar fashion, and I'm wondering whether the mirror is large enough for a 15" panel and 327mm triplet. Still undecided about split/non-split but I'm going to start off using the OHP's fused 220/330 fresnels.

Also, in this type of configuration (mirror connected and very close to triplet), is moving that assembly vertically (closer and farther from field fresnel) essentially the same as moving the triplet horizontally, or is the distance from mirror to triplet a critical factor?

Any thoughts? Thanks!