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Dust alert on the K-5

Discussion in 'Pentax Chat' started by Monobod, Jul 7, 2014.

  1. Monobod

    Monobod Phantom of the forum


    I am beginning to have doubts about the dust alert function on my K-5. This morning I decided to check the sensor for dust. I had no reason to suspect that there was anything wrong, but this afternoon I will be going out for some image hunting.

    Running the dust alert, showed several, no numerous dust streaks all over the sensor. So I ran the dust removal routine and check again. Still lots of apparent dust but in a different place this time. Mirror up and a good blow out with a Rocket blower and repeat the process. Still showing dust, but moving around.

    If this is for real, it does not look like sticky stuff (Pollen?) as that would stay put in one place. So I repeat the blower and check again. This time it says it has almost gone, so another couple of sensor shakes and check. But it is saying more than last time.

    I then set the camera up facing a reasonably clean white emulsion painted wall in the house, check that the focus is spot on and take a couple of shots in RAW. I load these into ACR, convert to psd's and then pixel peep at 100%, scanning across the image from top to bottom. There is no sign whatsoever of dust bunnies or hairs or anything else. I did spot a couple of blemishes that might have been dust, but I checked the wall and they were there for real.

    What is going on do you think? Is the 'Reveal Dust' routine ultra sensitive to the point where is sees dust that is not apparent on an image, or is it unreliable?

    Since I have had this camera, I have only twice spotted small circular dust bunnies on an image and they were removed by shaking the sensor a couple of times. I have never had to clean it in any other way, so I have not introduced contaminants and I'm very careful when changing lenses. I'm a bit puzzled to be honest.

    I suppose the thing to do is ignore it and carry on if there is nothing to be seen in the images, but of course, if a potential buyer or a camera dealer taking it in part exchange ran this routine, it could cost me money or a lost sale.

    Sometimes I wonder if the technology isn't just a wee bit too clever for its own good.

    Any thoughts?
    Last edited: Jul 7, 2014
  2. El_Sid

    El_Sid Well-Known Member

    Ignore it. If the real test shot reveals no dust under intense scrutiny then there is no dust. What you can actually see is more reliable than some dubious gimmick.
  3. AlexMonro

    AlexMonro Old Grand Part Deux

    I would've thought that when checking for dust, you want a plain background that's OUT of focus as much as possible, at the smallest aperture available.

    I don't know much about the "Reveal Dust" feature. Dust has never been a problem on my K20D - never done a sensor clean in over 6 years, just the sensor shake at switch on. I do sometimes change lenses out of doors. too!

    I've had a play with the Dust Alert as it seems to be called on my K3 (bought 2nd hand with around 9000 shots!) and that just seems to give a totally blank white screen every time. I've certainly never seen any actual signs of dust in the pictures (although, due to health issues, I haven't had much of a chance to use it yet).

    I would say that if you don't see any dust in your pictures, you don't have too much to worry about, except, perhaps, the resale issues. You could try doing a manual dust check again (out of focus blank background, min aperture) just to reassure yourself.

    I think I tend to agree with your last point... :)
  4. Monobod

    Monobod Phantom of the forum

    I'm not sure why out of focus is important? Can you explain that Alex? Anyway here are the images of the dust taken by the camera's dust reveal function and the picture of the wall. The dark bit at the top is a picture frame.

    https://flic.kr/p/od1TZuDUST-1s https://flic.kr/p/od1TZu by Monobod https://www.flickr.com/people//, on Flickr[/IMG][​IMG]
    https://flic.kr/p/od1TZ9DUST-2s https://flic.kr/p/od1TZ9 by Monobod https://www.flickr.com/people//, on Flickr[/IMG][​IMG]
    https://flic.kr/p/nXyENZWALL https://flic.kr/p/nXyENZ by Monobod https://www.flickr.com/people//, on Flickr[/IMG]
  5. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    I wonder if your permissions need a revision if you're trying to share your images?
  6. AlexMonro

    AlexMonro Old Grand Part Deux

    I can't see the images either - just the "Image unavailable" Flickr message.

    However, the reason for keeping the image OoF is to reduce the chance of any marks on the wall or whatever being mistaken for dust. If you're certain that your blank wall is completely uniform, down to the pixel resolution of the camera, it makes no difference - but I know none of my walls are that perfect, and even the grey cloud in the sky I was using today to check would probably have a bird flying across it at just the wrong moment!

    Using the minimum aperture makes the lens effectively a point source of illumination, so any dust (which is probably on the sensor cover glass, as much as 4mm in front of the optical plane of the sensor itself) is likely to cast a sharper shadow, and so be more visible.
  7. Monobod

    Monobod Phantom of the forum


    Sorry about the images being 'private', now corrected. I hope you can see them now. The 'dust' is really heavy in these two shots, which is unusual to say the least.

    I understand your comments about the out of focus state and I will try that too. Strange situation, I have very seldom had any dust problem with this camera, but I understand that there are sticky pads inside the camera wich are supposed to trap dust, perhaps these need replacing after a few years?? I may hava a chat with Pentax about this.
  8. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    Not yet.
  9. Monobod

    Monobod Phantom of the forum

    Interestingly, I have just run the 'Reveal Dust' again and it shows that the sensor is completely clean. I have been out today taking photos, turning the camera on and off numerous times. Perhaps that has finally shifted whatever may have been there?

    What a relief....:)
  10. Monobod

    Monobod Phantom of the forum


    Try pressing F5 to refresh the page, or go to the Flickr site. Hope that works.
  11. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    Refreshing doesn't work in my case for the embedded images, but going to your Flickr site now does.

    I used to scare myself with dust bunnies (Canon 5D original) by shooting test images at F/22 or similar, whereas in normal practice, I rarely use apertures smaller than F/8. Now that my bodies incorporate shakers and sticky pads or whatever, the problem does seem to have gone away.
  12. AlexMonro

    AlexMonro Old Grand Part Deux

    I finally got to see the images by going to Flickr, and I can see why the Dust Alert images got you worried!

    The pic of the wall doesn't look too bad to me, at least at that resolution. Ideally I'd like to look at a full size image to be really sure. It certainly makes it clear that the Dust Alert pics are unreliable, shall we say.

    I used to have a lot of dust problems with my Fuji S3 Pro - a rocket blower would shift a lot of it, but there were always a few spots. I got a lot of practice at cloning and spot heal... :)
  13. Monobod

    Monobod Phantom of the forum


    Now that you have seen them, I will take them down from Flickr. Don't want to encourage dissenters to criticise Pentax. The Reveal Dust option has done this to me before and I wonder if the software over emphasises the dust to make it obvious, thus creating a frightening scenario.

    All is well that ends well.
  14. El_Sid

    El_Sid Well-Known Member

    Must say that was my first thought when I looked at the examples.

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