[jomaga]

Hey Tom, 8etty and all of the fantastic people in this forum!

Some of you could help me to do a slide projector emitting a MXI texture to a screen?
I tried a plane emitting through a lens (to concetrate the light), and the result was upside down (it doesn´t matter), and very blurry. I´va changed a lot of lens types and a lot of distances between projector and screen, but no success.

Another challenge, Tom

(and how about a SSS retro-projection screen?)

[jomaga]

No hints?

[Mihai]

Well I was hoping with the sss we could render things like transparent film, a clear plastic material that we could texture, but so far it's a limited sss we have so what you want is not possible at the moment. Perhaps you could fake it with clipmaps if you really wanted, but they are also broken for now

[tom]

why not mihai? there is mxi
jose, can you give some real life dimensions of the projector you're dealing with?
i mean lens diameters, angles etc...

[jomaga]

I wish to test it with no fakes (if it´s possible), fist of all only a screen with no SSS for clear front projection (hard), and when I will have success, then SSS clear plastic screen with an mxi rear emision (harder)

[jomaga]

yes, Tom, I have to go now, but today (later) I want to do the max model with the right dimensions
thx

[tom]

oh all right... you're talking about the translucent screen...hmmm.
IMO it should work but as I said we need some real life dimensions for such a setup.

[hdesbois]

so, why not a 24*36 mm slide projected at a few meters.
HD

[jomaga]

I am trying to obtain some result, but i only have this blurry projection, because MXI emission is not parallel, as real life. I have to do a correction of the light dispersion with some lenses, but I don´t know exactly how to do (distances, type of lenses - convex, concave). I have to rotate the mxi mapping because the projected image was upside down.

The projection scheme should be like this:


the mxi image:


And the blurry result:

[hdesbois]

try convex or biconvex lenses with focal lenght about 80 or 100 mm.
HD

[Mihai]

But I thought the lenses are there to focus the light BEFORE hitting the transparent surface. I don't think this mxi emitter/projector thing will work as you want.

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[hdesbois]

Hem, I don't think so. Actually, you have to sets of lenses in a slide projector. One, usually a single one, is used to focus the light on the slide. We can dispense with it, since here the slide itself is an emitter. The other one, much more complex, is used to focus the light coming from the slide on the screen. Think of it as a camera working the reverse way.
I don't know the formula to find the exact point where the image on the screen is in focus, but I suppose you have to put the slide closer to the lens than the focal lenght.
Some useful techninal info about real world photography here :
http://www.galerie-photo.com/technique.html
(in french)
HD

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[jomaga]

Thanks for your interest whiskey, hdesbois,
I have some charts of projection distance and focal lenght, that´s not the problem.
My main dificulty is to know how a projector works, how many lenses, with wich shape, how much distance between them, etc. I have here a proffesional projector, and looking the objective, seem to be two lenses, one concave near the emitter and one convex outside, but probably have another inside to contro the focus. And, where is the emitter? Very close to the inside lens? And, how big is it?
I could make a section of my objective, but the cost (900€) is a little bit too expensive to cut it