40D Problem w/ "Hot Spot"

[BryanKing]

My 40D has developed a problem with recording some sort of hot spot in the image (always in the same spot). Can anyone tell me what this is? Is it dust somewhere, or an actual problem with the sensor?


Following are a few images to try to explain. These are 100% crops. When I open a raw image in DPP, I see a very clear 2x2 pixels that are a few different shades of deep red, but saving images to either jpg or tif of course show affects of resampling, aliasing or whatever.


The first image is a 100% crop from an out of focus background. The second is from a completely under-exposed shot (completely black). I don't think either of these really capture the essence of the problem, but it is the best I could come up with. It is really annoying, the spot inevitably showing up right in someone's dark hair, etc. It happens to be in the upper intersection of 1/3 points, right where I'm always trying to place the subject.


[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.30.36/HotSpot2.JPG[/img]


[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.30.36/HotSpot3.jpg[/img]

[BryanKing]

Holy cow it's fixed. Found this info on dpreview's forum, and it actually worked. My hot pixels are gone now.





1. Remove the lens and replace the body cap
2. Put the camera in manual cleaning mode with the body cap in place. You might be able to do this with the lens on, but I have always removed it and I don't argue with success.


3. Leave the camera in manual cleaning mode for maybe a minute or so.
4. Check to see if the hot pixel is gone.
5. If not, repeat the procedure once or twice more.

[alexniedra]

Wow - That could have become really annoying. Glad to see you fixed it.


Now go and shoot! [H]

[Oren]

That's a dead pixel on your sensor, but don't worry, there is no sensor without dead pixels... even brand new cameras from the factory have dead pixels (yes many, not one). The thing is that the camera map these pixels and fix it using its software.


It seem that this time your camera hadn't catch this one and therefore didn't fix it. When you put the cap, which is totally black, the camera had been able to catch/"see" this dead pixel more easily and then mapped it in its memory. So now the camera "knows" there is a dead pixel there and fixes it on every picture that you take.


I hope that helped... cheers.

[BryanKing]

Thanks so much for the explanation. Even though I found the tip over at dpreview's forum, there was no plausible explanation of why this may have fixed the hot pixel. In fact, the opinion seemed to be that this was a largely mythical fix to the problem. I can testify it worked for me, getting the camera to map the dead pixil and turn it off.


I assume that the sensor could continue to loose pixels, that they should be automatically de-activated by the camera, and I would never know. The software must just be filling in the dead area with color approximated from the surrounding area. Is there ever a point where the image would have noticeable degredation?

[Oren]

Is there ever a point where the image would have noticeable degredation?
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Well I'm no expert and even though that as I said, "many" pixels might be dead before even leaving the factory, I don't really have any information about just how many is "many" LOL. With that said, I'm still sure that the answer to yous question is: no.


Think about it. Let's say that as many as 10,000 pixels are dead - that's as low as 0.1% of your 40D's 10MP. Let's say that even 100,000 are dead - that's only 1% of your sensor... I think you get the point.

[kilofilms]

Well that one dead pixel sure was noticable for the time being.