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Is my CCD Sensor messed up?

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Offline brhibler1

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Is my CCD Sensor messed up?
« on: 13 / August / 2012, 23:11:42 »
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I installed CHDK a few months back for astrophotography.
The first few nights were great, taking 30sec-2min exposures.
Sometime after my pics started being over exposed in the upper left corner even with blackout/covered lens shots that are more than 15seconds.
Tonight I got the camera back out and removed the CHDK and all the scripts from the SD card. When I use the Tv camera setting at the camera's max, 15seconds, the pics are fine.

So I reinstalled CHDK and new scripts. Still anything over 15secs and upper left corner is over exposed.

Any idea's?
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Offline reyalp

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Re: Is my CCD Sensor messed up?
« Reply #1 on: 13 / August / 2012, 23:31:11 »
Sounds like amp glow. It's normal. There is a reason Canon defaults don't go over 15 sec.  If you google something like remove amp glow, you should find some techniques for dealing with it.
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Offline brhibler1

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Re: Is my CCD Sensor messed up?
« Reply #2 on: 13 / August / 2012, 23:33:01 »
I'll check that out!
Thanks!
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Offline waterwingz

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Re: Is my CCD Sensor messed up?
« Reply #3 on: 13 / August / 2012, 23:39:32 »
Quote from: reyalp on 13 / August / 2012, 23:31:11
Sounds like amp glow. It's normal. There is a reason Canon defaults don't go over 15 sec.  If you google something like remove amp glow, you should find some techniques for dealing with it.
Did some fast clicking but didn't see anything that implies this gets worse with camera age ?  The OP did not report seeing that when his camera was new.

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Offline brhibler1

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Re: Is my CCD Sensor messed up?
« Reply #4 on: 13 / August / 2012, 23:45:17 »
That's true. It just recently started doing it.
But I did research amp glow and found someone else with the same issue/same glow in same corner.
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Offline waterwingz

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Re: Is my CCD Sensor messed up?
« Reply #5 on: 14 / August / 2012, 00:15:59 »
Quote from: brhibler1 on 13 / August / 2012, 23:45:17
It just recently started doing it.
With all due respect,  are you sure ?  Or have you become more discerning and particular as you become better at this ?
 
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Offline philmoz

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Re: Is my CCD Sensor messed up?
« Reply #6 on: 14 / August / 2012, 00:25:12 »
Quote from: brhibler1 on 13 / August / 2012, 23:45:17
That's true. It just recently started doing it.
But I did research amp glow and found someone else with the same issue/same glow in same corner.

Amp glow is often temperature dependent and can also be affected by ISO.

If you live in the northern hemisphere then a few months ago the ambient temperature may well have been lower than it is now. As a consequence the operating temperature of the camera may have been lower.

Phil.
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Offline brhibler1

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Re: Is my CCD Sensor messed up?
« Reply #7 on: 14 / August / 2012, 00:48:57 »
It could be a heat issue.
I do live in central Texas!

I tried a few 20-30 second exposures with different settings.
I guess that before I had noise reduction on, because that's the only way that I can take pixs with no purple blur in the upper right corner.
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Offline reyalp

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Re: Is my CCD Sensor messed up?
« Reply #8 on: 14 / August / 2012, 01:16:47 »
Quote from: brhibler1 on 14 / August / 2012, 00:48:57
I tried a few 20-30 second exposures with different settings.
I guess that before I had noise reduction on, because that's the only way that I can take pixs with no purple blur in the upper right corner.
Dark frame subtraction (probably what you are referring to as noise reduction, makes shooting take 2x as long as exposure time) should help a lot. The canon firmware does this by default if the exposure is over about 3 seconds, but CHDK can force it on or off. Note that if you force it off with CHDK, you can still do dark frame subtraction on your PC later. This will work best with raw but is probably better than nothing on jpegs. Astrophotography sites should have good information about this.

I doubt it appeared suddenly, it's a characteristic most digital imagers and AFAIK every powershot tested with long exposures shows it. As Phil says, it is affected by other factors so it might have been less apparent in some shots.
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