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Thread: Neutral Density Filter For Projector

  1. #1
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    Default Neutral Density Filter For Projector

    Bit of an odd request here...

    I use a 3w projector (Kvant Clubmax 3000) but I find that the projector is often too bright for the small spaces I use it in. My solution up to this point has been to use black projection screens but this is not ideal (excessive power needed, easy to burn, etc.) I also can't just turn down the power in software because this greatly reduces the dynamic range of colors the projector can produce.

    Now I'm looking into using a neutral density filter to attenuate the output at the projector. I hope this will make my shows safer and more efficient while maintaining the full range of colors the projector can produce. I also won't need to haul a custom screen around to every show.

    The one thing I'm not sure of is what type of filter to use. I'm mainly curious about reflections back into the projector. I could use a cheaper standard absorptive filter but I'm not sure if the inherent reflections that will be present are a problem. There are more expensive filters with coatings that reduce the amount of reflected light to under 2% but I only want to use them if necessary. Do you think a little reflection of the output back into the projector poses any kind of problem?

    Generated heat and the resulting stress may also be an issue but I think it won't matter as long of the filter is of reasonable quality since the projector is only 3w.

    Any help would be greatly appreciated.

    -Connor F./Laser Pictures

  2. #2
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    swamidog is offline Jr. Woodchuckington Janitor III, Esq.
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    A standard issue camera ND filter will be fine. Just angle it so the reflections are not directed back into your projector.


    Quote Originally Posted by Glrock View Post
    Bit of an odd request here...

    I use a 3w projector (Kvant Clubmax 3000) but I find that the projector is often too bright for the small spaces I use it in. My solution up to this point has been to use black projection screens but this is not ideal (excessive power needed, easy to burn, etc.) I also can't just turn down the power in software because this greatly reduces the dynamic range of colors the projector can produce.

    Now I'm looking into using a neutral density filter to attenuate the output at the projector. I hope this will make my shows safer and more efficient while maintaining the full range of colors the projector can produce. I also won't need to haul a custom screen around to every show.

    The one thing I'm not sure of is what type of filter to use. I'm mainly curious about reflections back into the projector. I could use a cheaper standard absorptive filter but I'm not sure if the inherent reflections that will be present are a problem. There are more expensive filters with coatings that reduce the amount of reflected light to under 2% but I only want to use them if necessary. Do you think a little reflection of the output back into the projector poses any kind of problem?

    Generated heat and the resulting stress may also be an issue but I think it won't matter as long of the filter is of reasonable quality since the projector is only 3w.

    Any help would be greatly appreciated.

    -Connor F./Laser Pictures
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

  3. #3
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    Should have thought of that one...

    I suppose I didn't because I planned on eventually mounting the filter on the projector itself. I figured I might be able to mount it in place of the current shutter for a very low profile solution. This would still be ideal for traveling with and it's my end goal. Trouble is mounting it flush against the projector would send reflections directly inside the unit.

    I suppose I could make a box to house the filter and contain the reflections for SELEM.

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    if you place a standard camera ND filter where the shutter is before the galvos you will 100% melt it. They're not designed for that kind of power density. Something like this will perform better. https://www.thorlabs.com/newgrouppag...tgroup_id=5022

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    And just a reminder that even with a professional reflective ND filter that is designed for a static CW laser beam, you still need to angle the filter so the reflected portion does not travel back along the beam path and re-enter the diode(s) as Chris mentioned above. (This is especially important if you mount the filter in the beam path before the scanners.)

    Adam

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    Thanks for all the help.

    Araugh, I had initially planned to put the filter outside of the projector so I could easily add/remove it as needed but putting it inside would be convenient because it wouldn't add any bulk to the setup and the housing would make a good beam dump. I may do this eventually but I probably won't now since I don't want to void my warranty and I'm still experimenting.

    It seems like I should construct a box that holds the filter at an angle in front of the projector and also captures the reflections. I'll probably use a high quality filter from Thorlabs or a similar manufacturer. I'm still unsure about which kind to use though. A colored glass (absorptive type) seems the most convenient since the reflections will be weaker and more easily captured but I'm a little worried it might crack if it receives over a watt of heat from a bright effect or hot beam.

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    Try to readjust the color pallet after you lower the brightness in the software.

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    araugh is right. You should not use an ND filter on a laser.. you will melt it.. it's not made for these kinds of energy densities.. You should use it on a camera only..

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    Use black colored screen material. This is surprisingly amazing. Increases contract too as it attenuated all stray light.

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