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DLPLCR65EVM: Interference bands when coupling DMD into microscope

Malte Ahlers
Prodigy 230 points
Part Number: DLPLCR65EVM

Tool/software:

Hi!

I have a question concerning DMD optics/imaging. I’m well aware that my question is beyond the scope of this forum. However, I still would like to ask, maybe I’m lucky and someone can help or has some idea.

I am trying to couple the image of a Lightcrafter 6500 into a microscope. Since the LC 6500 comes without any optics, I attached a light engine I salvaged from an old DLP projector. In principle the setup works well: with the light engine and the original lens of the projector, I can use the LC 6500 to project images e.g. on a wall with good image quality. 

I’m using the camera port of the microscope to couple-in the image from the light crafter. Technically, a camera without any further optics is meant to be connected to this optical port. I’m using this port in reverse: with the DMD in the imaging plane, its image is projected onto the object under the microscope. That does actually work pretty well, however, with one major problem: I have strong interference patterns in the image. I.e., when using broad-band white light, I see blurry colored bands overlaying the image. When using monochromatic light, I have intensity gradients in the image. I guess this effect is due to the DMD acting as a diffraction grating. I see the same phenomenon if I use a lens between the DMD and the image plane of the camera port. Interestingly, if I use the original lens and project onto a matt screen, the interference pattern is not visible. So it seems like that I get these interference patterns as soon as I enter the microscope, even if I can produce an interference free image on a matt screen placed in the imaging plane.

Does anybody have an idea what to do to get rid of the interference? Any help is greatly appreciated!

Thanks a lot!

Malte

  • 0
    TI__Guru 54320 points

    Hello Malte,

    It would be very helpful to have a picture of what you are seeing.  I suspect that the effective NA of the original lens system is large enough that it does not see variations in tilt angle across the DMD, but that the system you are seeing it in has a much smaller NA (larger f#) which will show up variations that can exist across a DMD (+/- 1 degree).

    Fizix

  • 0 in reply to Fizix
    Prodigy 230 points

    Hi Fizix!

    Thanks a lot for the quick response! The problem with providing pictures is that I am using the dedicated camera port of the microscope to input the Lightcrafter image. Accordingly, I had to improvise to take representative pictures. I used an external macro-camera focused on the image plane of the microscope objective to record the DMD image projected through the microscope.


    The attached pictures show the main problem but have also additional problems that are only due to the quick-and-dirty approach of obtaining them. The blue-yellowish/greenish distortions on contrast edges in the horizontal axis (the letters in the first  picture) are not the problem. I don’t see it through the eye-pieces of the microscope. I think they are due to the improvised external macro imaging setup. The phenomenon I actually want to avoid is the turquoise-magenta pattern in the background. It's visible very similarly through the eye-pieces of the microscope.


    Btw, if I look directly onto the working DMD by naked eye, I see a similar color phenomenon, probably more colorful. But, as stated in my previous post, using the original optics of the salvaged light engine the image looks spatially neutral in terms of colors (no colored areas) when projected on a matt screen.


    Please let me know if I can provide more information that might help in identifying the problem.

    Thanks a lot for your support!

    Malte

  • 0 in reply to Malte Ahlers
    TI__Guru 54320 points

    Hello Malte,

    I would like to consult with our Optical Team on this.  If they want more information I will post back.  Please allow a couple of days.

    Fizix

  • 0 in reply to Fizix
    Prodigy 230 points

    Thank you very much!

  • 0 in reply to Malte Ahlers
    TI__Guru 54320 points

    I will post back after I have talked with them.

  • 0 in reply to Fizix
    Prodigy 230 points

    Sorry to bother you, but did you hear anything from your optics team yet? Thanks! Malte. 

  • 0
    TI__Intellectual 1700 points

    Hello , 

    Fizix is currently out of office and will be returning on February 3rd. Please note there may be a delay in his response, but he will get back to you as soon as possible. We appreciate your patience! 

    Regards, 

    Tristan Bottone 

  • 0 in reply to Tristan Bottone
    Prodigy 230 points

    Hi Tristan! Thanks a lot for the quick response. I'm very much looking forward to Fizix resonse! Best, Malte.

  • 0 in reply to Malte Ahlers
    TI__Genius 11800 points

    Hello Malte,

    Thanks for waiting!

    Best,

    Aaron

  • 0 in reply to Aaron Black
    TI__Guru 54320 points

    Hello Malte,

    I would like to see if I can set up a telephone conversation with you.  Please accept a friend invite.

    Fizix

  • 0 in reply to Fizix
    Prodigy 230 points

    Hi! Sorry for the delayed response! I accepted your friend invite some time ago. I would like to come back to your kind offer to talk on telephone about the problem at some point, however, I currently have another problem with the device that I can't solve. I will open another thread about that and come back to this topic later. Thanks again! Best, Malte. 

  • 0 in reply to Malte Ahlers
    TI__Guru 54320 points

    Hello Malte,

    No worries.  Let's work on your other issue first as you said.

    Fizix