iso sx230 - General Discussion and Assistance - CHDK Forum
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iso sx230

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Offline brustino

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iso sx230
« on: 25 / March / 2013, 18:48:14 »
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hi, how i decrease iso with chdk?
i would obtain long exposition time in condition of many ligth.
ciao and thank's.


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Offline waterwingz

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Re: iso sx230
« Reply #1 on: 25 / March / 2013, 18:50:30 »
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Offline reyalp

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Re: iso sx230
« Reply #2 on: 25 / March / 2013, 22:38:31 »
Quote from: brustino on 25 / March / 2013, 18:48:14
hi, how i decrease iso with chdk?
i would obtain long exposition time in condition of many ligth.
In general, CHDK does not enable you to decrease ISO below the factory limit.
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Offline brustino

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Re: iso sx230
« Reply #3 on: 26 / March / 2013, 07:00:56 »
thank's but if i try 1 sec and f8 in day ligth whit 16 iso the pic is total white is normally?
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Offline waterwingz

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Re: iso sx230
« Reply #4 on: 26 / March / 2013, 08:43:17 »
Quote from: brustino on 26 / March / 2013, 07:00:56
thank's but if i try 1 sec and f8 in day ligth whit 16 iso the pic is total white is normally?
This sounds normal.  You asked the camera for ISO 16 but that's lower than the camera can go.  You can only override the ISO value down to the factory limit (as reyalp said)  - which is typically around ISO 80.   So even though you asked for ISO 16, the camera took the picture using ISO 80 and was thus overexposed.
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Offline brustino

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Re: iso sx230
« Reply #5 on: 26 / March / 2013, 09:54:58 »
thank, there aren't mode for long exposure with dayligth?
override diafram??or....???
bye
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Offline waterwingz

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Re: iso sx230
« Reply #6 on: 26 / March / 2013, 10:07:44 »
Quote from: brustino on 26 / March / 2013, 09:54:58
thank, there aren't mode for long exposure with dayligth?
override diafram??or....???
The sx230 has an adjustable diaphragm but it can only be stopped down to f8. What you can try is to manually over-riding the camera's internal ND filter from the CHDK menu to be on,  set the ISO to 50, and the experiment with how slow you can set the shutter manually and still get an acceptable exposure.

Or even better,  put a darker ND filter in front of the lens and set the exposure manually with CHDK.

Why do you want to make long exposures in bright light ?   A differnt approach might be to make many short exposures and combine them using stacking software on your PC?
« Last Edit: 26 / March / 2013, 10:47:02 by waterwingz »
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Offline msl

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Re: iso sx230
« Reply #7 on: 26 / March / 2013, 14:16:40 »
Quote from: waterwingz on 26 / March / 2013, 08:43:17
You can only override the ISO value down to the factory limit (as reyalp said)  - which is typically around ISO 80.
It's not quite right.

The SX230/220 has a factory limit of ISO100 and f8. With  the CHDK overrides you have chance to go one or two steps outside the factory limit. My experience says ISO50(market) and f11 are possible. There are differences in the histogram.

You can also use the in-built ND filter.

msl
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Offline waterwingz

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Re: iso sx230
« Reply #8 on: 26 / March / 2013, 14:35:26 »
Quote from: msl on 26 / March / 2013, 14:16:40
My experience says ISO50(market) and f11 are possible. There are differences in the histogram.
The f8 limit is a mechanical one - something has to physically get smaller to change the iris diameter.  Its seem unlikely that Canon would put a mechanism in place that can go to f11 and then restrict it to f8.  Why would they purposely lower the spec of a camera in the competitive marketplace?  More likely,  you observed f11 when the iris was at f8 and the ND filter was in place ?
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Offline reyalp

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Re: iso sx230
« Reply #9 on: 26 / March / 2013, 17:01:20 »
Quote from: msl on 26 / March / 2013, 14:16:40
My experience says ISO50(market) and f11 are possible. There are differences in the histogram.
Fair enough, though 1 stop isn't going to get the OP what he wants.
Quote from: waterwingz on 26 / March / 2013, 14:35:26
The f8 limit is a mechanical one - something has to physically get smaller to change the iris diameter.  Its seem unlikely that Canon would put a mechanism in place that can go to f11 and then restrict it to f8.  Why would they purposely lower the spec of a camera in the competitive marketplace?  More likely,  you observed f11 when the iris was at f8 and the ND filter was in place ?
Actually, this has been observed and documented since the very early days of CHDK, on cameras without an ND. The iris seems able to go a bit tighter than canon firmware limit on some cameras.
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