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CHDK and Canon G9 ISO 3200 question

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Offline drobbie

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CHDK and Canon G9 ISO 3200 question
« on: 05 / August / 2014, 12:11:33 »
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Would it be possible to somehow override the ISO of a Canon G9 to 3200.  Although the ISO control only goes to 1600 there is a special SCN mode of ISO 3200.  If I use the override in CHDK the G9 seems to be pegged at 1600 i.e. I don't see a corresponding adjustment to shutter speed from a value of ISO 1600.

Using the SCN mode ISO 3200 mode produces a RAW that consist of a partial frame with 3 reduced images of different colours.

Not too terribly important but I just wanted to try some astrophotography stacking at ISO 3200 vs 1600.

By the way sub ISO 80 overrides seem to work ok at least shutter times adjust according but I have never tried any real shots at those values.

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Offline waterwingz

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Re: CHDK and Canon G9 ISO 3200 question
« Reply #1 on: 05 / August / 2014, 13:34:13 »
You won't see a "corresponding adjustment to shutter speed" regardless of what ISO override value you select with CHDK.  The Canon firmware is unaware of CHDK overrides and does not compensate when you use them. It assumes it still has full control.
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Offline drobbie

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Re: CHDK and Canon G9 ISO 3200 question
« Reply #2 on: 05 / August / 2014, 13:57:07 »
Ok I did a more accurate test at the low ISO .... I was wrong no change in shutter speeds.  So the G9 is pegged at the standard range on the dial.

Is that because of the ISOTable values in /CHDK/blob/master/platform/g9/shooting.c or some other constraint of the camera?  Do you think extending the table to include a value of 7 for ISO 3200 could work?
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Offline reyalp

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Re: CHDK and Canon G9 ISO 3200 question
« Reply #3 on: 05 / August / 2014, 17:32:40 »
Quote from: drobbie on 05 / August / 2014, 13:57:07
Do you think extending the table to include a value of 7 for ISO 3200 could work?
No, the "ISO3200" scene mode is most likely a special binning mode, not the same as regular ISO adjustment.

Generally speaking, CHDK ISO overrides do not let you go beyond the factory limits.
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