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Using CHDK Canon IXUS 125 HS camera with a UAV

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Offline paul.pelletier.771

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Using CHDK Canon IXUS 125 HS camera with a UAV
« on: 06 / October / 2013, 03:19:03 »
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Hello all,

I am flying a UAV equipped with a  Canon IXUS 125 HS.

In order to reduce  image blur caused by slow exposition time Tv, I am trying to configure the camera with CHDK .

With CHDK, I fix  exposure time Tv to 1/500 and use Auto ISo however I get sometimes overexposed pictures with f/2.7 and then some under exposed pictures with f/8.

It seems that this Canon cannot fix the Av...

Does anyone know of a way to fix this?
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Offline waterwingz

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Re: Using CHDK Canon IXUS 125 HS camera with a UAV
« Reply #1 on: 06 / October / 2013, 09:35:55 »
Quote from: paul.pelletier.771 on 06 / October / 2013, 03:19:03
With CHDK, I fix  exposure time Tv to 1/500 and use Auto ISo however I get sometimes overexposed pictures with f/2.7 and then some under exposed pictures with f/8.
What you are seeing is the camera inserting its internal ND filter (neutral density) automatically as it tries to correct for bright light situations.   The CHDK AutoISO code does not manage Av or ND filter settings - its technically a bug I guess.

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It seems that this Canon cannot fix the Av...
The IXUS125 does not have an adjustable aperture built into its lens - the Av setting is fixed.  The camera can only adjust exposure time (Tv) and ISO sensitivity (Sv).    Any variation in Av you might see is due to the effective f-stop changing at different zoom positions (focal lengths).

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Does anyone know of a way to fix this?
You might want to read and follow this thread :

http://chdk.setepontos.com/index.php?topic=10754.0

Otherwise,  try using the CHDK ND filter override menu item to force the ND filter to stay out.  You could also add  a command to  any intervalometer script you are using :  set_nd_filter()
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