QSI 6120ws CCD camera capture LED screen photo problem

Discussion in 'Image Capture' started by sqzeng, Jul 4, 2019.

  1. sqzeng

    sqzeng Standard User

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    I use the 6120ws to take the photo of a small LED screen. I expose the led screen three times. The first time I adjust lens focus to make photo blur as left-top in the picture, the led point picture has black triple. Secondly, with the same lens focus, increased the exposure time, also make a photo as right-top in the picture. Thirdly, I adjust the lens focus to take a clearly photo, the left led and right led on the screen have a different bright spot.
    And i try to rotate the sreen, the led pixels also looks like shift the same direction. And I use LRGB filters to take the photo, the phenomena still exists. The filters with an anti-reflection coating.

    Does any experts know what the problem is?
     

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  2. Colin Haig

    Colin Haig Staff Member

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    Are you using MaxIm DL Pro to obtain the images?

    There cold be several problems here.
    Is this a TFT / LCD / LED backlit display? An OLED display? What kind of display technology?
    Often the light is polarized by the LCD that is backlit by the LEDs.
    Is is swept? (row and column multiplexed) If so, exposure time could be part of the problem.
    The LEDs themselves may have lenses that are part of your issue.
    Collimation of your optics may be an issue as well. What lenses are you using, how much magnification?
    Please describe your optical setup.
     
  3. Doug

    Doug Staff Member

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    I'll add that if the light source isn't right in the center of the lens field of view you will very likely have optical aberrations. These will be especially obvious on point sources. Most likely you are observing the behavior of the lens, not the LEDs or the camera.
     
  4. sqzeng

    sqzeng Standard User

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    Yes, I’m using MaxIm DL Pro.
    The screen is a LED arrays with 2mm gap packaged. I have used canon 70d camera to take the led photo which is 24bit RGB, and the shift phenomenon was not exist although it is swept.
    The cooler camera is quantum scientific imaging (qsi6120ws) and the lens is TAMRON 18-300mm (the same as canon 70d lens). I also used a adapter ring to mount the lens.

    [​IMG] LED screen module upload_2019-7-8_10-29-9.png canon70d photo
    upload_2019-7-8_10-35-48.png
     

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  5. sqzeng

    sqzeng Standard User

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    The screen is relatively small, and the distance between camera and screen is lagre.
    If i use the same lens in canon70d and qsi camera, i think the phenomenon is not caused by lens, is that correct?
     
  6. Doug

    Doug Staff Member

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    It's very hard to say from the limited information available, but if I had to guess...

    The QSI camera has much wider spectral response than the DSLR camera; in particular, it will see more IR than the DSLR will. It's entirely likely that the lens doesn't work well in IR since it wasn't designed for it.

    I'd suggest putting an IR cut filter in there, to eliminate that possibility.
     
  7. sqzeng

    sqzeng Standard User

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    I don't konw the spectral response of canon70d.
    But I also used the LRGB filters to take the LED pictures, the problem still exists. The LRGB filters and the IR cut filter have the same function.
    The curves as follows:
    upload_2019-7-8_13-39-58.png LRGB filters curves upload_2019-7-8_13-40-24.png
     
  8. Doug

    Doug Staff Member

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    It's hard to know what is going on here from the available data. If you can post two RAW images taken under identical conditions from the two cameras, that would be a more useful comparison.
     
  9. Colin Haig

    Colin Haig Staff Member

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    I also suggest you contact QSI as they supplied the camera, and probably the filters as well.
     
  10. William B

    William B Cyanogen Customer

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    Not too sure what the question is that you are asking?

    In your image from the opening post, only the fourth picture of the group, bottom right, is properly focused. Picture number three, bottom left, is still not quite in focus and as a result the 'bright' spot is very slightly smeared, you can see this better by stretching the image in MaxIm DL, (re-posted stretched image attached below)
    The fourth image, bottom right appears just as I would expect for a monochrome camera and is accurately portraying the light distribution of a typical LED.

    The light emitting junction of a typical single colour, bi-colour or tri-ciolour LED is tiny in comparison to the body size of the LED and rarely at the geometric centre. This will be apparent as you rotate the panel, the bright emitting spot will follow the rotation. A further optical aberration may occur with LEDs that incorporate a moulded lens as part of the body design as the moulded lenses are not precision optical components.

    You can not compare directly the DSLR image with the QSI image because the DSLR incorporates an anti aliasing filter directly in front of the sensor array and this reduces spatial resolution, in addition the DSLR will be employing some level of pre-post processing to smooth the image, AFAIK very few DSLR's output a truly native RAW image from the sensor and image resolution becomes even worse if you are working with compressed JPG images from a DSLR. Only your monochrome QSI, or other make of dedicated monochrome astronomy camera using a CCD detector, will accurately record and output an image with no appreciable processing artefacts other than quantisation errors.

    The 'ring' artefacts seen in the LEDs of the out-of-focus pictures, one, two and three, are most likely wavefront artefacts generated in the camera lens, possibly due to the interference filters you are using and the very narrow bandwidth of the LED output wavelengths, simple lens defects or a combination of the above. You could try imaging the panel with an empty filter slot in the QSI and see if the ring artefacts are still present in the out-of-focus image through the empty filter slot, if so, then the most likely answer lies with lens wavefront errors as the camera lens groups are no longer spaced correctly at intra-focal and extra-focal positions.

    To summarise, referring back to your original in-focus picture number four, bottom right, that looks quite normal and is not showing any problem with the QSI camera, lens or filters.

    If you are intending to use the LED panel as a flats light source you will need one or more diffusing elements between the LED panel and the camera.

    Stretched.jpg
     
  11. sqzeng

    sqzeng Standard User

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    Thanks everyone, i have solved this problem .
    The reason is that the default aparture of lens is maximum value, when i adjust the aparture to F22, it worked correct.
     

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  12. Colin Haig

    Colin Haig Staff Member

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    That would do it! If you need to open the lens up, it should still be okay up to maybe f/8 or a bit more.
     

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