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Help with getting long exposure times - A640 only works when flash fires?

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Offline RhodeIsland

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Help with getting long exposure times - A640 only works when flash fires?
« on: 13 / August / 2015, 08:55:20 »
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Hello, I'm trying to take night time pictures, and I can set the shutter speed to 59s via the CHDK override menu, but this setting appears to only work if I leave the camera in Tv mode and allow the flash to fire.

Is this right, or am I missing something?
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Offline srsa_4c

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #1 on: 13 / August / 2015, 17:52:34 »
Quote from: RhodeIsland on 13 / August / 2015, 08:55:20
Hello, I'm trying to take night time pictures, and I can set the shutter speed to 59s via the CHDK override menu, but this setting appears to only work if I leave the camera in Tv mode and allow the flash to fire.

Is this right, or am I missing something?
Which version of CHDK are you using? (Name of the .zip file you used to install or "Miscellaneous Stuff" -> "Show Build Info" in the CHDK menu.)
If it's pre-1.3, try installing a more recent release.
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Offline RhodeIsland

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #2 on: 13 / August / 2015, 21:50:21 »
I'm running 1.3.    I will admit to not reading the whole manual - I'm assuming there must be some setting which honors the 59sec override?   Auto?   Program?
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Offline reyalp

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #3 on: 13 / August / 2015, 22:47:42 »
Quote from: RhodeIsland on 13 / August / 2015, 21:50:21
I'm running 1.3.    I will admit to not reading the whole manual - I'm assuming there must be some setting which honors the 59sec override?   Auto?   Program?
Shutter override should work in pretty much any mode, but there may well be bugs.

Modes that allow manual shutter speed input (Tv, M) may behave differently than modes that don't.

Do shorter overrides work?
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Offline RhodeIsland

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #4 on: 14 / August / 2015, 18:43:44 »
I haven't tried other than 59seconds which appears to be the max I can set.   If I leave it in Tv mode I can get it up to 15sec (default maximum) but in other modes it's essentially instant.
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Offline srsa_4c

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #5 on: 15 / August / 2015, 05:25:27 »
Quote from: RhodeIsland on 14 / August / 2015, 18:43:44
I haven't tried other than 59seconds which appears to be the max I can set.   If I leave it in Tv mode I can get it up to 15sec (default maximum) but in other modes it's essentially instant.
Are you sure you're using the latest available 1.3 release? Parts of the a640 code were rewritten about a year ago, and long exposures were tested successfully.
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Offline reyalp

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #6 on: 15 / August / 2015, 15:05:36 »
Quote from: RhodeIsland on 14 / August / 2015, 18:43:44
I haven't tried other than 59seconds which appears to be the max I can set.   If I leave it in Tv mode I can get it up to 15sec (default maximum) but in other modes it's essentially instant.
If you are using the current version, this may be confusion about the UI. Use the zoom buttons to switch between seconds, minutes and hours in longexp mode.

Quote from: srsa_4c on 15 / August / 2015, 05:25:27
Are you sure you're using the latest available 1.3 release? Parts of the a640 code were rewritten about a year ago, and long exposures were tested successfully.
Note that extended Tv support uses a different codepath, so it's possible overrides work for >64s but not for lower values.
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Offline RhodeIsland

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #7 on: 22 / August / 2015, 22:10:35 »
The weird thing is that I can get 59s exposures, but only when I leave the flash on.   Using the zoom option I can set longer shutter speeds, thanks.

I mean, am I doing this wrong somehow?
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Offline reyalp

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #8 on: 22 / August / 2015, 22:27:43 »
Quote from: RhodeIsland on 22 / August / 2015, 22:10:35
The weird thing is that I can get 59s exposures, but only when I leave the flash on.   Using the zoom option I can set longer shutter speeds, thanks.
This almost certainly means there is a bug in the port. There might be other factors that influence whether it works or not. For example, overrides could be broken if you press the shutter quickly without waiting for the camera to focus. It's also possible that other settings like shooting mode, ISO or something else could play a role. You mentioned earlier that it only works at all in Tv mode, which is strange. In general overrides should work in pretty much any mode, and it should almost certainly work in M if it works in Tv.

If you set a 1 minute 10 second exposure does that work without the flash?  I ask because CHDK uses somewhat different code for overrides longer than 64 seconds.
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Offline RhodeIsland

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Re: Help with getting long exposure times - A640 only works when flash fires?
« Reply #9 on: 03 / September / 2015, 20:28:34 »
Sorry for the late response.   If I do 1:10 it only works with the flash.   In Tv mode.
« Last Edit: 03 / September / 2015, 20:30:41 by RhodeIsland »
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