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Hot pixels? Please help me diagnose a problem with my Rebel XT

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Thread started 04 Apr 2005 (Monday) 22:45   
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nater
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Hello everybody. I've been playing around with my new Rebel XT from Dell, and I decided to try testing for hot/dead pixels. I took 1- and 30-second exposures with the lens cap on, and found one dead pixel (white) and one or a couple hot pixels (blue). Then I took some pics of my white walls, and found much more interesting results. In the resized example pic below, you can identify 40+ dark spots.

Are these hot/dead pixels? If so, why did only a couple show up in the lens-capped pictures?

I know what the problem is not. It is not my lens (problem happens with both of my lenses), or my walls (identical pattern of spots appears when photographing various white walls and ceiling).

Does anyone have thoughts? It seems like a significant problem to me, so I'm planning to call Dell tomorrow and ask for a replacement. Is there something I'm missing? Thanks for any help...

- Nate

(edit: the quality of my uploaded pic is quite diminished, but you can still see the strange dark spots I'm referring to)

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Post #1, Apr 04, 2005 22:45:30


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Dante ­ King
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looks like a dirty sensor. If so its easily fixed by blowing (rocket blower or the like) or a cleaning outlined in many threads on this forum.

Post #2, Apr 04, 2005 22:49:03


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ssim
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You've got yourself a case of dust bunnies. As Dante says, try the blower first and then you might have to clean your sensor. It is fairly straight forward and easy to do.

Post #3, Apr 04, 2005 23:02:22


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nater
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Thanks for the advice. I have a dinky little brush blower, and I had tried blowing on the sensor (after removing the brush) to no avail. I just tried it again, more vigorously, and maybe 1/3 of the spots are gone. I guess I'll need to invest in an industrial-strength blower... :)

Post #4, Apr 04, 2005 23:10:54


Canon 70D || Canon 10-22 f/3.5-4.5 || Canon 17-55 f/2.8 IS || Canon 24-105 f/4L || Canon 70-200 f/2.8L IS || Sigma 30 f/1.4 || Canon 50 f/1.4 || Canon 85 f/1.8 || Canon 60 f/2.8 Macro || Rokinon 8 f/3.5 fisheye
Feisol CT-3401N Tripod || Kirk BH-3 Ballhead
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eosster
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Looks like a just a dust to me, time for a good clean up and good luck, you'll need it.

Post #5, Apr 04, 2005 23:29:03


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hedphonz
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i would think that there is also another problem that your camera is too small. jk. i would agree with everyone else that you have a case of the dust bunnies.

Post #6, Apr 04, 2005 23:41:01




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robertwgross
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That's sensor snot.

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Post #7, Apr 04, 2005 23:48:58 as a reply to hedphonz's post 7 minutes earlier.




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tim
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You can purchase a kit to clean your sensor hereexternal link. Many people have done it, and very few people have any problems. I do it myself, it took some practice to do it well, but it was easy. DO the practice swipe suggested, or a couple, to get the technique correct before trying on your camera.

If you're not confident, Canon I think clean sensors for free within their warranty period, and some stores may clean it quicker or while you wait even.

If the camera is brand new and you've not used it anywhere dusty, it's not unreasonable to return it and ask for a clean one, but you're not guaranteed to get one any better than your current one.

Post #8, Apr 04, 2005 23:49:10


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nater
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WarrenO wrote:
blowing with your mouth is a very bad idea... all you need is spit on it and you have a much bigger mess.. get the right tools and you won't have issues. Did you just get this? (dirt) If so why is it so dirty? About the dead pixel...hmmm never even thought of that myself... I will check for that...

Thanks...

Warren

I didn't use my mouth. I used a cheapo blower that came in a camera cleaning kit, minus the brush.

And the camera is brand new -- I haven't even taken this one outside yet. I have no idea how it could be so terribly dirty.

Post #9, Apr 05, 2005 05:32:19 as a reply to post 481820


Canon 70D || Canon 10-22 f/3.5-4.5 || Canon 17-55 f/2.8 IS || Canon 24-105 f/4L || Canon 70-200 f/2.8L IS || Sigma 30 f/1.4 || Canon 50 f/1.4 || Canon 85 f/1.8 || Canon 60 f/2.8 Macro || Rokinon 8 f/3.5 fisheye
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Toogy
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I'm curious as to what your aperture was when you took that shot?

Post #10, Apr 05, 2005 06:08:54


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drisley
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Simplest cleaning method.... Giottos Rocket Blowerexternal link.
Those dinky little blowers just are not big enough.
As far as the hot pixel test goes, if you only have one at long exposures, that is a very good result :)

Post #11, Apr 05, 2005 06:17:12


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nitsch
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I had this exact same problem when I got my 300D. The first ones sensor was filthy but otherwise the camera appeared to be brand new. I think some of them must just pick up more sensor crud than others during assembly. The marks were clearly visible from about f11 upwards so I returned it to the shop and asked for it to be swapped for another new one (although the sales assistant originally suggested they send it to be cleaned at my expense LOL! I don't think so!). The next one was a lot better but still not perfect when examined at about f32 however seeing as I'm never going to use this aperture in real life I decided not to let it bother me too much.

I have yet to clean the sensor but when the time comes I'm not too worried about doing it. I guess I have just accepted now that cleaning my sensor will have to become a routine maintenance task with a DSLR. It's just a bit of a shock to discover this issue when you move from film or point and shoot.

Post #12, Apr 05, 2005 08:09:06




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nater
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Toogy wrote:
I'm curious as to what your aperture was when you took that shot?

I had set the camera to Tv. I just checked the pic, and it says the aperture was set to f/36. I'll do some tests at lunchtime to see how much shows up at wider apertures.

BTW - Based on the excessive dirt, and the hot/dead pixels, Dell has already agreed to ship me a replacement. And they didn't give me any hassle about it.

Post #13, Apr 05, 2005 09:09:59 as a reply to Toogy's post 3 hours earlier.


Canon 70D || Canon 10-22 f/3.5-4.5 || Canon 17-55 f/2.8 IS || Canon 24-105 f/4L || Canon 70-200 f/2.8L IS || Sigma 30 f/1.4 || Canon 50 f/1.4 || Canon 85 f/1.8 || Canon 60 f/2.8 Macro || Rokinon 8 f/3.5 fisheye
Feisol CT-3401N Tripod || Kirk BH-3 Ballhead
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drisley
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Nater, odds are the next one you get will be just as bad or worse!
For an F36 picture, that is actually a fairly clean sensor. And having one hot pixel at more than 1 second is also very, very good.
You could go nitsch's route and demand return after return after return, but I think you would have to go thru the entire canon stock before you got a new DSLR with a completely dust free sensor, and without any hot pixels. In fact, I've read MANY stories of people exchanging their DSLR's because of 1 or two hot pixels at long exposures. Usually after going thru 3 or more cameras, they want the first one back because it had fewer hot pixels than the rest.
I don't think there is a single DSLR out there that won't show atleast 1 hot pixel on a 1+ second exposure.
And there definately isn't a single DSLR out there that doesn't have some dust on the sensor. And if there was, it would only take a few days of use before it did.

Post #14, Apr 05, 2005 11:50:24


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Toogy
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I would bet that IF I took a picture of a wall at F36 I would have just as much dust if not more. But will I ever take a picture of a wall at F36?
I guess what I am saying is that if you start to notice it in 'normal' photographs, that is when you really have a problem.

PS, stop taking pics of your lens cap!!! ;)

Post #15, Apr 05, 2005 12:20:19


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