Sensor getting hot? Problem with noise in images after time - General Discussion and Assistance - CHDK Forum supplierdeeply

Sensor getting hot? Problem with noise in images after time

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The camera in question is a Canon A470.
Last night I set up a sunset script (sunset5.bas as I recall) which is very good at night photography btw, and pointed my camera at Polaris. I did as continuous an exposure as possible. There was 1 second between shots, and after each exposure it took several seconds for the images to save to the SD card. Between the exposures, saving, and the 1 second delay I got about 4 shots per minute. After about 45 minutes of this, the images started getting noisy. Also, the file size started getting bigger, probably due to the noise in the image. At 7.1mp, they started at 1mb per, and ended up at almost 3mb per image after a couple of hours, with a LOT of noise in the image.

Looking at the meta data in the pix in Picasa, the exposure was 15s on all the noisier pictures but between 8 and 13 seconds on the less noisy ones. ISO and everything else was the same. The only thing I can think of is that the CCD sensor is getting overheated and introducing noise. I've posted samples of each here:

https://plus.google.com/photos/109190891124377551497/albums/5874599449734535745?authkey=COqqp4fR-bvUvAE

Thanks for any input on how to minimize or solve this problem. Maybe I just need to give it 15-30 seconds between exposures to cool down. The ambient temperature last night was fairly cool (not cold).

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Offline reyalp

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Re: Sensor getting hot? Problem with noise in images after time
« Reply #1 on: 05 / May / 2013, 17:16:22 »
Looking at the meta data in the pix in Picasa, the exposure was 15s on all the noisier pictures but between 8 and 13 seconds on the less noisy ones. ISO and everything else was the same. The only thing I can think of is that the CCD sensor is getting overheated and introducing noise. I've posted samples of each here:
Longer exposures give you more noise. Higher sensor temps also give you more noise. This is all expected, normal operation of digital cameras.

Normally, the Canon firmware does a "dark frame" for exposures longer than about 3 seconds.  This takes a second shot with the shutter closed, and subtracts it from the first.

If you have automatic darkframe disabled (the script might be doing this), you might want to do dark frames in your post processing.

Stacking multiple shorter exposures will average some of the noise.

If you look at astrophotography sites and forums, you should find a lot of useful information for dealing with this kind of thing.

Quote
https://plus.google.com/photos/109190891124377551497/albums/5874599449734535745?authkey=COqqp4fR-bvUvAE
I get "you do not have access" message on this link
Don't forget what the H stands for.

Re: Sensor getting hot? Problem with noise in images after time
« Reply #2 on: 05 / May / 2013, 17:24:34 »
Here's a different script you might want to look at that addresses some of reyalp's comments :

http://chdk.wikia.com/wiki/Meteor_Intervalometer_with_Dark_Frame_Managment

Ported :   A1200    SD940   G10    Powershot N    G16

Re: Sensor getting hot? Problem with noise in images after time
« Reply #3 on: 05 / May / 2013, 17:28:26 »
You guys are so helpful. Thank you! I fixed the link. I'll check out that other script too. I have had so much fun with CHDK and my PowerShot cameras. I'm so glad it exists. I can't afford so-called "real" photography. A cousin suggested a $1500 camera for my star trail photos and I told him "Why would I do that, I wouldn't have nearly as much fun!".


Re: Sensor getting hot? Problem with noise in images after time
« Reply #4 on: 05 / May / 2013, 17:31:18 »
I have to admit ignorance on the whole 'dark frame' concept. It makes sense, but I don't know what to do with the dark frames that are produced.

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Offline reyalp

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Re: Sensor getting hot? Problem with noise in images after time
« Reply #5 on: 05 / May / 2013, 17:40:22 »
I have to admit ignorance on the whole 'dark frame' concept. It makes sense, but I don't know what to do with the dark frames that are produced.
As I said, you can find a lot of information about this on astrophotography sites. You can do simple subtraction in gimp or photoshop, but if you are processing a whole timelapse you probably want to set up a workflow that lets you do it all at once.

Here's a random google result: http://www.astropix.com/HTML/J_DIGIT/JPG_DFS.HTM

You can also probably find some useful threads on the forum (search darkframe or "dark frame")
Don't forget what the H stands for.

Re: Sensor getting hot? Problem with noise in images after time
« Reply #6 on: 05 / May / 2013, 20:48:59 »
Thank you for that. I have some googling to do! I had issues using that meteor.lua script.

I get an error ":26: your CHDKS does not support native calls"

I'm using 1.0.0-1699, and I realize 1.1 is out, but the download link is down.

Re: Sensor getting hot? Problem with noise in images after time
« Reply #7 on: 05 / May / 2013, 20:57:16 »
Thank you for that. I have some googling to do! I had issues using that meteor.lua script.

I get an error ":26: your CHDKS does not support native calls"

I'm using 1.0.0-1699, and I realize 1.1 is out, but the download link is down.
I think that you actually need to use 1.2.0 to use that script (it allows you to enable native calls from the CHDK Miscellaneous menu).

Regardless.  the 1.0.0 version of CHDK is getting really old.  You'll run into more and more issues trying to use it.

Ported :   A1200    SD940   G10    Powershot N    G16


Re: Sensor getting hot? Problem with noise in images after time
« Reply #8 on: 05 / May / 2013, 21:24:35 »
Great, I'll give that a shot. Now just gotta wait for the download page to be working.

Re: Sensor getting hot? Problem with noise in images after time
« Reply #9 on: 05 / May / 2013, 21:30:24 »
Great, I'll give that a shot. Now just gotta wait for the download page to be working.
What download page are you using ?

http://mighty-hoernsche.de/

and

http://mighty-hoernsche.de/trunk/ 

are working just fine for me.
Ported :   A1200    SD940   G10    Powershot N    G16

 

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