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Dark Pictures from SD700IS - Can CHDK Help?

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Offline jonno

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Dark Pictures from SD700IS - Can CHDK Help?
« on: 27 / October / 2008, 16:58:41 »
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Hi. A few months ago my SD700IS started taking very dark pictures on a random basis. I usually leave the camera in Auto mode but if I can override this in Manual mode I haven't figured out how (I'm a complete camera novice but eager to learn).
When this happens the picture on the lcd display seems fine until I press the button to focus, at which point the picture gets way too dark - as do my pictures. I can sometimes get a good picture by turning off/on the camera so I think there is an intermittent problem with some light sensor but I'm just guessing.

I was wondering if CHDK could help me figure out what is happening but I don't really know what to look for. Is there something in it that would tell me the light level that is being sensed? What are the parameters I should be looking for? Is there a manual override for the light setting?

I love the camera and want to continue using it but my wife is going nuts with it. Is it worth taking it to a repair shop or will it cost more to open it up than it's worth?

Any help appreciated,

Jonno.
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Offline ewavr

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #1 on: 27 / October / 2008, 17:14:49 »
Very similar thing happens with my friend's SD500 - after half-press of shutter button image is too dark, but shaking of camera can help.
Probably cause of this failure is dust in ND filter mechanics. He plans to disassemble the camera for lens cleaning.
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Offline jonno

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #2 on: 27 / October / 2008, 17:18:56 »
Hmm, well I did take the camera apart a while back to replace a broken lcd screen. I wonder if I got dust in there at that time. I will try shaking to see if that does anything.
Sorry for the dumb question but what does ND stand for? If I take it apart to clean where should I be looking for dust?
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Offline fudgey

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #3 on: 27 / October / 2008, 17:27:29 »
Neutral Density filter. Sunglasses inside the lens to be less scientific. Your camera doesn't have an iris in its aperture to adjust the amount of light getting to the sensor, it has an ND filter to reduce light when it's too bright for ISO 100 instead because it's cheaper and smaller than an iris.

I would've guessed ND filter failure as well.

You could try overriding the ND filter state in CHDK, it's possible you could get lucky and that could make the camera never switch it on to the position where it might get stuck. Of course that means your pictures will be overexposed if it's very very very sunny.
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Offline ewavr

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #4 on: 27 / October / 2008, 17:32:25 »
Quote from: jonno on 27 / October / 2008, 17:18:56
Sorry for the dumb question but what does ND stand for? If I take it apart to clean where should I be looking for dust?

Sorry, I did not understand exactly your question due to my poor English.  :(
ND filter in IXUS cameras is built in lens - see this topic.
Besides, your camera can have different defect.
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Offline PhyrePhoX

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #5 on: 27 / October / 2008, 18:01:26 »
ewavr, your english is very good. and even if it was not good, don't be afraid to use the google translator ;) btw you might wanna join us in irc for a chat, might be worthwile :)
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Offline jonno

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #6 on: 28 / October / 2008, 11:45:17 »
Ok so I've tried to pin this down a little. I put the camera in Manual mode and fiddled with the ISO setting. I point the camera at a subject and gradually switch the ISO from 80-100-200-400-800 while checking at each setting. The ISO80 setting almost always goes dark when I press the button and then depending on the subject I'm looking at, somewhere at a higher ISO setting it will start operating normally

Is this the way it should work in Manual mode?

Update: Note that this is not consistent even with the same subject. Ie I just tried this again with the same subject (same lighting etc) and now even at ISO80 the picture looks fine.
« Last Edit: 28 / October / 2008, 12:09:47 by jonno »
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Offline jonno

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #7 on: 28 / October / 2008, 12:39:05 »
Here are 3 example photos taken in succession:
ISO 200
EXIF Data:
Shutter Speed = 1/500
Lens Aperture = F/2.8
Focal Length = 6mm
Metering Mode = Pattern
Exposure Comp = 0 step

ISO400
EXIF Data:
Shutter Speed = 1/250
Lens Aperture = F/5.6
Focal Length = 6mm
Metering Mode = Pattern
Exposure Comp = 0 step

Auto
Shutter Speed = 1/200
Lens Aperture = F/2.8
Focal Length = 6mm
Metering Mode = Pattern
Exposure Comp = 0 step


Every setting <= ISO200 is the same and every one >=ISO800 is the same (inc. auto).

However 10 minutes later I tried the same thing and AT FIRST the Auto setting AND the ISO80 setting game me the light picture. After changing the ISO a few times though it reverted to the sequence above.
« Last Edit: 28 / October / 2008, 13:10:32 by jonno »
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Offline Hacki

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #8 on: 28 / October / 2008, 12:55:06 »
It would have been quite helpful if you used a tool which doesnt remove the EXIF data to resize the images..
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Offline jonno

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Re: Dark Pictures from SD700IS - Can CHDK Help?
« Reply #9 on: 28 / October / 2008, 13:00:51 »
Quote from: Hacki on 28 / October / 2008, 12:55:06
It would have been quite helpful if you used a tool which doesnt remove the EXIF data to resize the images..


Do you mean picassaweb removed some data from the file? I can post the EXIF data if you let me know how to view it.
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