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Old Nov 27, 2006, 11:46 AM   #1
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I just have the new 5D for almost 2 weeks, and I discovered some bright sparks when I do the following:

I covered the len with the len cap and pressed the shutter, then I reviewed the picture with magnified, I discovered few bright sparks, I have changed the len and the sparks stayed the same place, I think this came from the sensor. Did anyone try this and has the same problem?
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Old Nov 27, 2006, 12:40 PM   #2
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Could be some hot pixels

I beleive (I'm pulling this from memory) if you set the date on the camera to December 1, turn it off and then back on the camera will check for bad pixels. Then set the date back to today and try the same expirement with the cap on.
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Old Nov 27, 2006, 8:11 PM   #3
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Remove your lens cap. You'll get better photos that way. ;-)

Leaving it on will cause slower shutter speeds, and since you don't have any light hitting the sensor, you can get some hot pixels testing one that way.

To be frank, I find it amusing when someone notices them with lens cap on type tests. At one time, these types of tests were helpful, since cameras didn't have any type of system to get rid of them. So, you wanted to try and find a camera that didn't have any at exposures of around one or two seconds. Even then, with low resolution sensors, you were "rolling the dice" on whether you'd get one that good or not.

With some newer non-DSLR cameras with smaller photosites, you can have hundreds of them with exposures of only a few seconds if noise reduction is turned off.

Hot pixels are when photosites record a higher value (brighter) than they should, usually with longer shutter speeds. When the problem occurs at faster shutter speeds, they're considered "stuck" (always bright).

Virtually all CCDs will have hot pixels in some conditions. The longer the shutter is open (and the darker the conditions since not enough photons are hitting the sensor) the more likely a photosite won't be linear in it's output when responding to light, and it will record a higher value than it should.

Temperature also impacts it (which is why you see cooling systems for sensors in digital cameras used in astronomy). The more you test for them, the more you'll likely have, especially without any light hitting the sensor.

You just don't see hot pixels with most newer cameras because of built in noise reduction to subtract them out on longer exposures, since the ones that occur at typical shutter speeds have already been mapped out at the factory.

Make sure your noise reduction is turned on. That's what it's there for (to remove hot pixels on longer exposures). It's not designed to remove the typical noise you see. It's entire purpose is to remove hot pixels on longer exposures.

Hot Pixels are normal on longer exposures. Your camera has a built in dark frame noise reduction system to try and locate them and map them out on longer exposures.

It works on photos taken longer than 1 second (where hot pixels usually show up). The way it works is by taking two photos. The first photo is of your subject. Then the camera automatically takes a second image using the same settings with the shutter closed.

The camera then notes the positions of any hot pixels in the "dark frame" (second) exposure, and maps them out of the actual exposure. It knows where to find them because the dark frame exposure was taken at the same time, using the same settings, with the camera at the same temperature. In most cases the hot pixel locations will be the same in both images using this technique. But, the longer the exposure, the greater the chance it will miss some of them.

If you have a pixel that is always hot (bright), even on shorter exposures in good light, then it's referred to as a "Stuck" pixel. The Long Exposure NR feature won't help for that.

In most cameras, when a camera develops a stuck pixel, a trip back to the manufacturer is needed. The manufacturer then updates a bad pixel table in EEPROM. When a photo is taken the image processing automatically checks the camera's bad pixel table and maps the pixel out (replaces it with values determined from adjacent pixels using sophisticated interpolation algorithms).

Some cameras allow the user to perform a bad pixel map themselves (a number of Olympus models have a menu choice that calls a procedure to locate and map out bad pixels).

KM DSLR models have an undocumented feature that checks and maps out bad pixels on a monthly basis that you can force by setting the date up one month if you don't want to wait after you see a bad one.

To force it, set your camera's date and time up to the last few minutes of the last day in the month.

Turn it off, and wait until enough time has passed for the internal clock to change months. Turn the camera back on, take some photos, and turn it off again.

Then, after you are sure the red led has gone out, turn it on and reset your date and time back to where it should be. Take some photos and see if the hot pixels are gone.

Note that this is *not* designed to remove hot pixels that occur on longer exposures (they're normal, and the noise reduction should get most of them if turned on, as it should kick in on exposures of around 1 second or longer).

The remap is only designed to map out pixels that are going to be hot on typical exposures (faster shutter speeds) You don't want it remapping pixels that only show up on long expoures since the noise reduction system's entire purpose is to remove those, and you can end up with a lot of them on a long exposure without noise reduction turned on with many cameras.

If you do have some at typical shutter speeds (with the lens cap off), it's probably best to perform a remap with a warm camera to make sure it finds them all (the warmer the sensor, the more likely they'll occur, and you'll want them to be bright enough to meet the threshold the camera is looking for before it remaps them).

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