Is it safe to use the Av override below hardware limit? - General Help and Assistance on using CHDK stable releases - CHDK Forum
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Is it safe to use the Av override below hardware limit?

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Offline TMHKR

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Is it safe to use the Av override below hardware limit?
« on: 15 / January / 2015, 16:46:02 »
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Hi there. I have the SX170, which has the aperture range of 3.5 - 8.0 (W) and 5.9 - 8.0 (T).

Since CHDK allows me to set it to 2.8 (there are even some negative values to choose!), is that setting actually possible? Or 3.5 is the hardware limit?

Sounds noobish, but I'm afraid I'll damage the aperture mechanism if I set it below or above its designated limit.

Thanks in advance.
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Offline reyalp

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Re: Is it safe to use the Av override below hardware limit?
« Reply #1 on: 15 / January / 2015, 17:05:57 »
Quote from: TMHKR on 15 / January / 2015, 16:46:02
Hi there. I have the SX170, which has the aperture range of 3.5 - 8.0 (W) and 5.9 - 8.0 (T).

Since CHDK allows me to set it to 2.8 (there are even some negative values to choose!), is that setting actually possible? Or 3.5 is the hardware limit?
The lower (larger aperture) limit in the Canon specs is almost certainly a hardware limit, because a "faster" lens would be a big selling point for Canon. Overrides higher than canon spec have been reported to work on some cameras, e.g you might be able to go to 16 at max zoom. The Canon firmware doesn't expose that option because it's not very useful.
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Sounds noobish, but I'm afraid I'll damage the aperture mechanism if I set it below or above its designated limit.
We can't answer that with certainty. I'm not aware of anyone who has damaged a camera with aperture overrides, but you could always be the first ;)
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Offline waterwingz

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Re: Is it safe to use the Av override below hardware limit?
« Reply #2 on: 15 / January / 2015, 18:03:05 »
Quote from: reyalp on 15 / January / 2015, 17:05:57
The Canon firmware doesn't expose that option because it's not very useful.
IIRC,  anybody who has reported being able to use a smaller aperature also reported that the resulting image quality was terrible.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline TMHKR

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Re: Is it safe to use the Av override below hardware limit?
« Reply #3 on: 15 / January / 2015, 19:37:27 »
So basically, can I use Av override to have, for example, 3.5 on max zoom? And the values are weird (there are even negative ones), I can choose these, in this order:

2.88, 3.02, 3.46, 4.05, 4.44, 4.95, 5.57, 6.08, 31.36, -5.-14, 8.62, -9.-38, 26.93, 18.22, 32.51, 7.09, 10.66, -18.-76

Somehow this override doesn't seem to be of any practical use to me. Yet.
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Offline waterwingz

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Re: Is it safe to use the Av override below hardware limit?
« Reply #4 on: 15 / January / 2015, 19:53:51 »
Quote from: TMHKR on 15 / January / 2015, 19:37:27
So basically, can I use Av override to have, for example, 3.5 on max zoom?
You can choose basically what you posted originally : 3.5 - 8.0 (W) and 5.9 - 8.0 (T).   So at wide angle you can use 3.5 to 8.0 -  when zoomed all the way in you can use 5.9 to 8.0

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And the values are weird (there are even negative ones), I can choose these, in this order:
2.88, 3.02, 3.46, 4.05, 4.44, 4.95, 5.57, 6.08, 31.36, -5.-14, 8.62, -9.-38, 26.93, 18.22, 32.51, 7.09, 10.66, -18.-76
That's bizarre and probably a bug in the port.  Where are seeing these values ?  The CHDK Enhanced Photo Operations menu -> Override Av menu item ?

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Somehow this override doesn't seem to be of any practical use to me. Yet.
It's useful if you are also overriding the ISO and shutter speed.  Once you override one,  you also need to override the other two to set the correct exposure.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline TMHKR

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  • Canon PowerShot SX170 IS (1.01a firmware)
Re: Is it safe to use the Av override below hardware limit?
« Reply #5 on: 16 / January / 2015, 07:02:55 »
Yes, these values are in Enhanced Photo Ops > Av Override. I'm using nafraf's pre-alpha port (1.3.0 / SX170 / 1.01a), which should be released as alpha to Autobuild any day now, since the RAW problems are fixed.
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