Dead Pixel Or Dust?

Discussion in 'Canon EOS' started by eric_guel, Sep 4, 2020.

  1. Hi, all.

    My 5D Mk IV has developed a black spot at small apertures, always in the same spot on the frame.

    I thought it was simply a dust spot, so I clean the sensor myself using a kit from Amazon. I cleaned it three times actually, but no luck. The spot remains.

    I try looking at the sensor, but can't see a spot. Granted it's hard, because everything is so reflective on it.

    My next thought was maybe it's a dead pixel, but seems that most dead pixels are not black.

    I'm attaching a sample of a file shot at f8 (one showing the full frame and the other cropped in). At 5.6 it's slightly visible and at f4 and lower it's practically imperceptible.

    Any ideas? Thanks, everyone!

    Eric

    Screen Shot 2020-09-04 at 12.32.55 PM.png

    Screen Shot 2020-09-04 at 12.33.06 PM.png
     
  2. That smudge looking thing on the right is on the paper, not the sensor.
     
  3. Way to big to be a dead pixel - looks like dirt to me. Did you try wet-cleaning? I had limited success removing dirt with a gel-stick and much better success with a lenspen sensorklear.
     
    William Kahn likes this.
  4. Thanks. Yes, well, the kit I used was a swab the size of the sensor and some sort of cleaning fluid. So must be a small, stubborn piece of dirt on there I'm thinking. I'll look into the lenspen. Thanks!
     
  5. A dead pixels would be one or a small group of individual pixels with no light recorded at all. A fuzzy blob of intermediate shade like this is definitely a shaddow usually caused by sensor muck. It can be difficult to clean off, especially if the cause is something like a pollen grain rather than dust.
     
  6. Would you recommend then having a professional clean the sensor? Would that likely do the trick?
     
  7. Hi, the fact that it changes with the aperture setting is pretty well conclusive that it's something on top of the sensor's cover glass. (If you stop the lens all the way down, say f/22, it should become very small, but pronounced).

    A further proof is to see if it shifts position with zooming. Shoot a test shot at both a short and long focal length (again, using a small physical aperture like f/22). Then examine the images in Photoshop, or whatever, to compare the exact position of the spot. Obviously it will not move at all if it's a sensor defect. Note that this test won't show movement under these two condition: 1) if the debris is dead center on the sensor (the farther off center, the more it will move), or 2) it's one of those special lenses with a fixed "exit pupil;" if so, use different lenses.

    What I would have done, back in the day, would have been to put the camera under one of those long-working-distance stereo zoom microscopes that can view from outside the camera body (the camera has lens removed, with shutter open). At, say 50x or so, you should be able to see the actual particle, assuming that you can get light on it. At the time I was specifically studying the makeup of such things with respect to purchase of a significant number of cameras. For your purposes you would at least have an idea what you were dealing with.

    Something to keep in mind is that every time you try to clean the sensor there is always a (tiny?) risk of of putting a tiny scratch in the cover glass. (This might happen if your cleaning material picks up a tiny particle of grit and you wipe this across the glass.) So make sure you are very meticulous in following the cleaning instructions. At some point, if you are not successful, it might be worth having the manufacturer do the cleaning. Good luck with it.
     
  8. I've never used a professional cleaning service, but they ought to do a better job of it than I do.:oops:
     
  9. I've always done my own. It's unnerving at first, but I've never done any damage. I start with a Rocket blower. If that doesn't work, I use a static brush holding the lens opening down. The final stage is using a wet swab (I use Eclipse solution). It sometimes takes more than one swabbing, and you have to be careful not to start beyond the sensor to avoid picking up grease or dirt.
     
  10. For what it's worth – I've cleaned sensors on my own cameras and those of some friends using PEC-Pads and Eclipse solution with very good results. Sometimes it takes only a swipe or two but -- it can be a real challenge to get some specks off that have been left in place for a long time. I removed a stubborn spot from a Canadian friend's 1DX that took 18 (the most ever) very damp, but NOT runny, pads before it turned loose. A clean work area with no air stirring is a must. I make only two swipes at a 5-7 degree angle with each pad – swipe left once – pick it up, turn it over and swipe right once then discard the pad. Test to see if the spot is gone. I repeat this process as many times as necessary until I get the debris. Nervous tenacity – it works.
     

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