1. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    Here's an interesting one.

    A customer recently hired a camera and lens from us. He complained that the sensor was very dusty and he sent us this test shot.

    The thing is, when we sent the camera to him, the sensor was spotless. We know how to clean sensors, and we're fussy. It was literally spotless at f/40.
    The camera came back today, and we tested the sensor, and again it is absolutely spotless.

    So what's that dark spot on his image?

    Technical info: Canon 6D Mk II, Canon 24-105mm f/4 Mk II. Image taken at ISO 320, 1/4000th at f/4.5. (Yes, f/4.5.)

    [​IMG]
     
  2. gramps

    gramps

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    The smaller one looks like an insecct of some sort to me ... I once had a small 'mite' inside the viewfinder of the camera I was using.
     
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  3. GreenNinja67

    GreenNinja67

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    Terry
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  4. Dave70D

    Dave70D

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    Hi Ho Silver away !
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    Gramps beat me to it, TRHS looks like a fly, so is it the lens instead.
     
  5. realspeed

    realspeed

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    it is a UFO, they come in all shapes I understand.:rolleyes:. The other one is a mark on your sensor I suspect
     
    Last edited: Sep 20, 2018
  6. Nostromo

    Nostromo

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    The right hand one looks like some kind of bug to me (the flying kind). The other spot does look like dust, which may have shifted in transport back to you, which is why you can't see it anymore.
     
  7. MatBin

    MatBin

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    1. Possible an insect got into the body in some way and moved into the sensor area after you cleaned it, it could have been there when you cleaned it or when the customer unboxed it and put a lens on?
    2. Looks like a dust bunny, again could quite easily have got in there post cleaning.

    Do you know when the customer spotted this, possibly post shoot and after one or more lens changes in a dusty environment.

    You know it was clean on despatch but I doubt they will agree with you, so it looks like a refund of some sort for the sake of goodwill might be in order, albeit unwarranted in real terms.
     
  8. Byker28i

    Byker28i

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    drone top right or fly
    dust spot on the lens - I have exactly the same on my 24-105, produces the same exact image spot
     
  9. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    We considered that. But we don't think it is.

    Our problem is that this photo was taken at f/4.5. We have never seen any dust spots that are (A) big enough to be visible at f/4.5, and also (B) small enough to show up as such a small opaque spot with such well defined edges. usually, if you have spots on the sensor, they might be well defined at (say) f/32, but then if you take more images at progressively wider apertures - f/22, f/16, f/11 etc - the spots get progressively larger and more diffuse. We simply cannot work out how this one can possibly be so small and well-defined at f/4.5.
     
  10. MatBin

    MatBin

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    Unless he added it in post processing so he'd get a refund, is that a bit cynical?
     
  11. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    Please explain. I have never seen a dust spot on a lens affect an image. And I can't conceive of how it might - even theoretically - affect an image taken at f/4.5.
     
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  12. Dave70D

    Dave70D

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    Sad if he is/has done that.
     
  13. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    He reported it pretty much as soon as he received the camera.
    We don't see any evidence of that. (Yes, I did think to look.) As far as I can tell, the image is straight out of the camera with no post-processing. If t had been post processed, I would expect to see evidence of it in the EXIF data, but there's nothing there.
     
  14. MatBin

    MatBin

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    Any chance your cleaning dept dropped a clanger and didnt clean it before despatch but have done it when received back, unlikely I know as I am sure they would have admitted it, after all it would be a simple mistake not a hanging crime.
    Can you repeat the problem with the lens you sent out on another body?
     
  15. PhilH04

    PhilH04

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    The right hand more defined object is definitely a fly or bee or similar that was flying through when he took the image. I can only speculate on the other less well defined spot and wonder if it could be a spot of moisture that has since evaporated, but that might leave a mark, but it is definitely something on the sensor that has more than likely now been dislodged.
     
  16. Peter Drought

    Peter Drought

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    Left hand one is very obviously dust on the sensor, which will be there whatever aperture you use as it sits "behind" the aperture in the camera. Not sure about the right. Looks like an insect, possibly on the front of the lens. Its visibility will depend on where the lens was focussed rather than the aperture per say, although that would affect the depth of field , and consequently how likely it would be that the object would be in the plane of focus.
     
  17. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    Examination of the full high-res image suggests that it is a fly.

    upload_2018-9-20_13-8-45.png

    But not a fly on the sensor, because it wouldn't be in such (almost) sharp focus at f/4.5.

    Interestingly, the EXIF data doesn't say what the focus distance was. If I were taking a shot of the sky to check for sensor dust, I would set the focus manually to the minimum focus distance, to ensure that there is no possibility of anything being in focus. But our customer clearly hasn't done that. The EXIF data says he used AI Focus, and the depth of field is from 11.94m to 14.77m, which suggests a focus distance of around 13.2 metres. Could that fly be 13 metres away? The length of its body is about 20 pixels on the full 26-megapixel, and that would correspond to 14mm length at a range of 13m. That's perhaps a bit big, but not ridiculously so. Perhaps it's about 10mm long and 9m away, which would be consistent with its pixel dimensions and also consistent with it being not quite in focus. So that's quite plausible.

    Still, it's the spot that has us intrigued.
     
  18. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    Sorry Peter, but that's just wrong. How many times have you tested sensors for dust? We do it dozens of times very week. As I explained earlier, if you have spots on the sensor, they might be well defined at (say) f/32, but then if you take more images at progressively wider apertures - f/22, f/16, f/11 etc - the spots get progressively larger and more diffuse.
     
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  19. Peter Drought

    Peter Drought

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    Any possibility that the customer opened it, inadvertently allowed dust in, and is then using this as an excuse for a refund? Not to be cynical, but some people can be like this.
     
  20. Peter Drought

    Peter Drought

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    You are thinking about dust on the front of the lens, not on the sensor. The sensor sits behind the aperture and so anything resting directly on it will be visible. The image (ie the light) of this "artifact" will not have had to pass through the aperture to get to the sensor, and so will be unaffected by it. Dust on the front element of the lens however is in front of the aperture. Conceivably it's visibility will be affected by the f stop (and also what distance the lens is focussed at).
     
  21. TonyHall

    TonyHall

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    Was the photo shot through a window? Ie. the fly/mark is on the window not on the sensor or lens.

    If the customer has a few images showing identical marks in identical positions then obviously not.
     
    Last edited: Sep 20, 2018
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  22. Nod

    Nod Kronus

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    The fly/bee shaped one is almost certainly a fly/bee - might the more central blob be another insect closer to the lens? Head on would give a fairly circular blob.
     
  23. Box Brownie

    Box Brownie

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    This seems to make some sense.....................a de-focused droplet of something on a window??? NB with the caveat that @TonyHall states!
     
  24. Dave70D

    Dave70D

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    Now that does sound about right, I have shot through the window before and thought I had dust but it was on the window.
     
  25. Byker28i

    Byker28i

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    I definitely get a round blob like that on my 24-105, in the same position every time, visible on sky only generally, that isn't on any other lens.
     
  26. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    Peter, how many times have you tested sensors? I've done it hundreds of times and I clearly described what you see at different apertures. I could post some examples if you like.

    What's happening with dust on the sensor is that when the aperture is small, the rays of light coming through the lens are more nearly parallel, and the dust casts a clear shadow on the sensor. When the aperture is larger, the rays of light come through the lens at more of a variety of angles, and the shadow is more diffuse. In front of the sensor there are various layers of glass, up to 4mm thick on some cameras, and so the dust is never actually on the sensor; it's always in front of it, and that's why the characteristics of the shadow can and do vary.

    If you still disagree, please explain why.
     
  27. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    We have a winner!

    Or at least, I think we do. What you're both suggesting is that the blob is a real image of something that was really in the customer's field of view when he pressed the shutter button, and not any kind of artefact. That's the tentative conclusion that we had reached here in the office. We're still waiting to hear back from the customer.
     
    Last edited: Sep 20, 2018
  28. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    But there are no marks on the lens?

    Do you see the blob at all apertures?
     
  29. Byker28i

    Byker28i

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    dunno - will try tonight when I get home
     
  30. Cagey75

    Cagey75

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    With all else cancelled out, I would have thought shot through a window, but even then it would have to have been shot at the wider end for it to show up
     
  31. Kell

    Kell

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    My old 600d used to produce a dark spot very similar to the blurs on the image and I think it was one particular lens (18-135) rather than anything in the body.

    It did, however, used to appear in exactly the same spot on every photo at the same size - which is why I thought it might be something in the camera as I thought it might appear different sizes with a zoom lens.
     
  32. Gazamonk

    Gazamonk

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    Ditto, seems unlikely.
     
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  33. jerry12953

    jerry12953

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    I have had a mite or some sort of tiny insect crawling around inside the viewfinder a couple of times. Don't know how they get there or how they get out, or what they do there. So could it be that?
     
  34. Terrywoodenpic

    Terrywoodenpic

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    The top right one is clearly a minute insect of some sort on the sensor. as it is alive it probably simply walked somewhere else when you checked the camera.
    the other blob might also be an insect but less defined because it was flying or jumping at the time and not in contact with the sensor.

    it would probably be as well to fumigate the camera and lens.
     
  35. Nod

    Nod Kronus

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    IF the insect is on the sensor, it's somewhere between 0.5 and 0.75mm long. (Based on measuring the "shadow" on my screen and reducing the dimension to what it would be on an FF sensor - insect is ~5mm long on my screen with the full frame being 250mm wide.)
     
  36. Alan Clogwyn

    Alan Clogwyn

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    I had a Wide angle which had a mark in the front element group and it would show at apertures of 4.5 or smaller. I had it cleaned off but it came back in the exact same spot.
     
  37. JPL

    JPL

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    Both insects. I photograph houses for a living and get this all the time in the gardens. Can take ages to take them out. They often appear as small out of focus elongated blobs ranging to, in rare occasions sharp flies. They tend to be the smaller midges rather than flies as the midges have a habit of hovering in the same place whereas flies are much faster moving and do not tend to show up.
     
  38. Kell

    Kell

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    How many shots did they send you?

    One shot could be dust on the outside of the lens, midges, flies, something in the air.

    Several shots of the same bur in the same place would indicate something in the camera/lens somewhere.
     
  39. david357

    david357

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    My guess is
    that the shot was taken through
    a window and the fly and the dirty mark on the window glass and therefore are out of focus, if that was how the shot was taken.
     
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  40. woof woof

    woof woof

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    Just want to add myself to the list of people who think the dust bunny like blob towards the centre of the picture is a living thing.

    I've had dust bunny like blobs like this at wider apertures several times when taking pictures at the seaside and they're there in one picture but not the next so I just assumed they are either birds or bugs.

    I too can't remember seeing a genuine dust bunny like that at anything like f4.5.
     

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