Interesting artifact

<p>After a day of shooting, I noticed what I can only describe as a "fuzzy squiggle" on some of my images.<br>

It is in the lower right corner of the attached pic. It only seemed to appear when that area of the subject matter was blue. It also seemed to change in density depending on either the shooting angle or the intensity of the blue background.<br>

The camera is a relatively recently acquired D50. which had only 1300 shutter actuations when I got it so I don't expect that age or heavy use is a factor unless there is deterioration of the sensor. I have been shooting and repairing for 50 or so years and am thoroughly familiar with all situations relating to dust, lint,<br>

q-tip fibers and lens brush bristles. The sensor appears to be spotless, as is the interior of the AF-D 70-300 lens. Any experience with this ? See attached</p>

<p>Here's the pic, internet is slow tonight<br>

four tries and all I get is "the website is too busy" will try later</p>

<p>Here goes again</p>

<p>once more</p><div></div>

<p>*looks like hair or thread... have you tried a different lens .. that will remove one factor .</p>

<p>Looks like what Garcia thread... er, said. Looks too sharp to be inside the lens to me (not from any experience - I've always got Nikon to do my cleaning) - I'm guessing that the low-pass filter isn't as spotless as you're hoping. Have you re-checked? (Fluff moves!) I hope it's not a scratch. Does it go away at large apertures? (Spending half my time at f/2 has been a wonderful way of not having to clean my sensor recently...)</p>

<p>AHA! - a fine example of the (in)famous blue pixel eating nematode .... :-)</p>

<p>The sensor isn't spotless, there is a hair/fiber on it.</p>

<p>I join with the others in thinking that just <em>has</em> to be a hair/fiber on the sensor. I'm sure you know it will be at the top of the sensor, since the picture is upside down.<br /> I don't think it could be so sharp if it were in the lens or elsewhere in the rig.</p>

<p>Maybe you don't see it now because it fell out? Or is it on new images out of the camera?</p>

<p>Then why isn't it on all my images ?</p>

<p>Visibility is going to depend on the aperture of the lens that you're shooting through. When you shoot wide open, the piece of lint might be nearly invisible. As you stop down it will become more visible. </p>

<p>Do a test. Shoot a blank wall or open sky with the lens wide open, then shoot again with it stopped all the way down. Your sensor will look spotless in the first shot. The second shot will reveal just how dirty it actually is... </p>

<p>Sometimes dirt on the sensor will be more visible at certain apertures.</p>

<p>Also, crud images get lost in the foliage, and the like, but show up beautifully on water or sky. Try pixel peeping at the same spot on other images and see if there is any blur there.</p>

<p>I am not sure why my new film camera ended up with all those loose threads coming out of the shutter seam on some days, BUT on the images they look quite like this when they do show up.</p>

<p>The tail of Loch Ness? ;) Without much difficulty I see at least three other blips caused by stuff on your sensor. The one you mention may have come and gone because it is has so much surface area that the slightest air movement created by the mirror or shutter causes it to migrate. Check your <em>sequential</em> series of photos. Has it disappeared only to reappear in the <em>exact</em> same location? Hmmm...</p>

<p>Does it move around? (No, not in the Nematode sense!) </p>

<p>I guess there's a bit of fibre in the mirror box/shutter area somewhere, a big Hurricane blower should see it off. </p>

<p>Sadly, the D50 doesn't have a cleaning function, but it looks pretty fuzzy, ie not in intimate contact with the sensor surface. Go on....Blow it Away!</p>

<p>I am sure it is a thread. I had a similar experience when shooting film on a Mamiya 330 F medium format camera. Took two rolls of film to cure it. Try shining infra red or ultra violet light into the camera body with the lens off and you may see something.<br>

Good luck<br>

</p>

<p>Did some blue sky shots at max aperture and minimum. The squiggle seems to be gone.<br>

Thanks, all for your insight.</p>

<p>Blue sky shots are over-rated. First of all you have to wait until daylight, and the sky has to be clear. A much easier approach is to stick the camera up to your computer screen when you're displaying a blank page on your word processor. It gives you a nice uniform white area, day or night (assuming your computer screen is clean).</p>

<p>I think the problem with using a sky, wall, or monitor screen is that, as I seem to remember in cases where I got dirt on my old 5D screen (a dust magnet if there ever was one) that aperture was one variable, but that the focal length on a zoom, and the distance to focus also played at least some role in making crud on the sensor more or less visible.<br>

I did a series of dawn shots and the dirt seemed to show up irregularly depending on more than just aperture. The relationship in any case was complicated since pictures taken with the same lens showed or did not show the spots and changing to another lens, made still different patterns seem to emerge. At least, without going over the pictures more carefully, that was my impression.</p>

<p>However, as a recent thread pointed out, the human mind WANTS patterns, and will impose them regardless (known as the "Martian Canal Syndrome").</p>