Sensor

[bill_force]

<p>I know very well what dust on a sensor looks like I an image (dark spot) but what does a minute scratch look like on the image, is it black or is it another like grey or white line? I have a very small almost invisible line on all images in the same place now.</p>

[Ed_Ingold]

<p>It could be a scratch. Have you cleaned the sensor or touched it in some way that could have scratched it? The sensor is covered with glass, but not particularly hard glass and probably coated.</p>

<p>To highlight anything on the protective glass, stop down all the way (e.g., f/22), point the camera at a featureless surface (e.g., open sky) and snap a picture. It doesn't matter if it is in focus or not. The small aperture will cast a hard shadow of any defect onto the sensor.</p>

<p>This is a severe test, akin to trying on swim suits under fluorescent light. Any dust or defect will be highlighted. If you're lucky, it could just be residue from an incomplete cleaning attempt.</p>

<p>Don't try to clean a dusty glass surface by rubbing. Dust can be abrasive and pervasive (southern Spain was a nightmare for me). Blow it off as best as possible (with a blower, not your breath), followed by a microfiber brush (e.g., Butterfly lens cleaning kit). In the worst case, use a folded, damp cleaning tissue like a brush. If you use a damp tissue, you'll then need to follow up with a careful cleaning using the Copperhill method (http://www.copperhillimages.com/index.php?pr=tutorials), using sensor swabs or PEC pads and Eclipse fluid (spectroscopic grade methanol). Touching the cleaning device or fluid with your finger will contaminate it with skin oil and leave streaks.</p>

<p>Sensor cleaning is serious business. You can do it yourself, but do your homework. Google is your friend (not to mention Photo.net).</p>

[bill_force]

<p>Thank you Edward but even though a long dissertation you didn't answer the question I asked IE: If in fact a scratch, what color would the scratch appear to be on an image. Dust is usually black or near black but I have no idea what color (white, grey, chartreus) a scratch would manifest itself on an image.</p>

[bill_force]

<p>Edward, I found the answer in one of Bob Atkins articles on sensor cleaning, thanks again for your reply.</p>

<h2>What’s the worst that can happen</h2>

<p>The worst that can happen is that you scratch the sensor while attempting to clean it. If you are careful and you use professional cleaning tools this is highly unlikely. Scratching can occur if you get a small piece of grit on the tissue you use to wipe the sensor. Commercial products for sensor cleaning are made in clean rooms and are very unlikely to be contaminated. A typical book of lens tissues is certainly more likely to be contaminated. They are cheaper, but the risk of damage is higher. The sensor covering filters isn’t especially delicate, in fact it’s similar to the coated filters you’d use on a lens, but even so it can be scratched.<br>

If you do scratch the sensor (or more accurately the front of the filter stack that covers the sensor), you’ll get a black line on every image and the filter over the sensor (or in some cases the whole sensor assembly) will have to be replaced.</p>

[sarah_fox]

<p>Bill, I once suffered a scratched "sensor." (To be more accurate, the AA/IR filter covering the sensor was scratched.) I am meticulous about keeping the entire mirror box clean (not just the sensor), but apparently a hair got into it and tangled up between the shutter blades, causing a wild enough excursion of one of the blades that the filter was scratched -- or so goes my theory. (I'm not talking about a tiny, thin little hair, but rather a very thick, somewhat long hair that I had to tease out from between my shutter blades.) You could see the scratch very clearly through a loupe, and when knowing where it was, also with your naked eye. It glistened a bit in the light. The shadow of the scratch had no color. It was gray, just like a dust spot. Canon replaced the filter for me for about $250, as I recall. I know repair costs vary considerably by camera model.</p>

[bobatkins]

<p>As quoted above, the scratch appearance will be much like like dust spots. It will look black or grey and be most noticeable at smaller apertures. The smaller the aperture the darker and more defined it will be.</p>

<p>If it's a scratch you can tell by shooting at various aperture and looking at the appearance. The density and width should change with aperture. If they don't then it could be a sensor defect (if it's in the vertical or horizontal direction), or a manufacturing defect on the <em>inside</em> of the sensor cover that you've only just noticed!</p>