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How to eliminate the diffraction light?

Heming Wei
Prodigy 140 points

I removed projection lens and want to design by ourselves. But I find the light from the DMD is not collimated. Is that true? There is some scattering light inside. I use a focusing lens and the image is not too clear. Is there an aperture in the projection optics?

Please give us some suggestions.

Thanks,

  • 0
    TI__Mastermind 30600 points

    Hi Heming Wei,

    You are correct on both accounts. The DMD needs optics to work correctly and there is an aperture in the projection optics. You can find the nominal value in the user's guide of the LCr4500, table 1-1: www.ti.com/.../dlpu011e.pdf

    For further optics help, we recommend that you reach out to our design network partners. They'll be able to provide you with great expertise and assistance with your custom optical configuration. e2e.ti.com/.../3404.design-network-partners

    Let me know if you have further questions.
    -Paul

  • 0 in reply to Paul Goedeke
    Prodigy 140 points
    Thanks Paul,

    So, if the light inside is not collimated, is there a diffuser prior to DMD?
    If yes, Can I remove this part?
  • 0 in reply to Heming Wei
    TI__Guru 54675 points

    Hello Heming,

    There is no diffuser in this system.  Typically in DLP projections systems the light is not collimated, but rather is a cone 1/2 angle cone of 12° around an input that is 24° from the DMD normal, so that the light reflected from the pixels forms a 1/2 angle cone of 12° centered on the DMD normal to go out the projection lens. 

    The LightCrafter 4500 is similar, but with a projection offset of 1 (i.e. the bottom of the screen image comes straight out of the projector, but the top edge is projected at angle to the optical axis so that the unit can sit on a table and still project up to the wall.

    Here is a good discussion of projector offset:  www.hcinema.de/.../infocus-in72-74-76-offset-en.pdf

    What are you attempting to accomplish?  Maybe we can give some suggestions.

    Fizix