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Max shutter time only 60 sec for A720

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Offline pannayar

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Max shutter time only 60 sec for A720
« on: 14 / December / 2012, 17:12:48 »
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CHDK provides only up to 60 (or 64 I think) seconds on the A720is.  This is not sufficient for shooting very low lit conditions at the lowest ISO.  On the A590 it provides upto 2040 seconds,  and I have used 256 seconds on one occasion.  Is this because of any hardware limitation on the A720?
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Offline lapser

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Re: Max shutter time only 60 sec for A720
« Reply #1 on: 14 / December / 2012, 22:11:53 »
This is a camera limit, not a CHDK limit. On my SX260, if I store a very long or very short shutter times directly to the camera with prop case locations, the maximums I get are 1/3200 and 64 seconds.
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Offline pannayar

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Re: Max shutter time only 60 sec for A720
« Reply #2 on: 14 / December / 2012, 22:22:00 »
Thank you, I thought so.  The CHDK manual says "Ultra-long shutter speeds - at least up to 64 seconds - and longer for supported cameras"...

The A720 and A590 are contemporaries, so I am a bit surprised the A720 has this limitation.
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Offline waterwingz

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Re: Max shutter time only 60 sec for A720
« Reply #3 on: 14 / December / 2012, 22:23:24 »
Quote from: pannayar on 14 / December / 2012, 22:22:00
The A720 and A590 are contemporaries, so I am a bit surprised the A720 has this limitation.
From what I can tell,  it seems to be just random luck.
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Offline philmoz

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Re: Max shutter time only 60 sec for A720
« Reply #4 on: 14 / December / 2012, 22:35:08 »
Long exposure overrides cause problems on the A720 so it is disabled.
http://chdk.setepontos.com/index.php?topic=6182.0

Phil.
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Offline pannayar

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Re: Max shutter time only 60 sec for A720
« Reply #5 on: 14 / December / 2012, 22:44:31 »
Thank you!  It is good to know why something is the way it is.
« Last Edit: 15 / December / 2012, 07:56:19 by pannayar »
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Offline reyalp

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Re: Max shutter time only 60 sec for A720
« Reply #6 on: 15 / December / 2012, 19:36:41 »
Quote from: pannayar on 14 / December / 2012, 22:44:31
Thank you!  It is good to know why something is the way it is.
FWIW, this should be fixable. My first guess would be a typo in the assembler for either the movie or long exposure code.
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Offline dvip

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Re: Max shutter time only 60 sec for A720
« Reply #7 on: 15 / December / 2012, 19:49:11 »
I can get around 30 secs using the A590IS-101b with a script like this.
You could replace 471 with 567 or other value and see if you get 60 secs.
I haven't used this for a while.

set_tv96_direct - 471
sleep 1000

press "shoot_half"   
sleep 1500
press "shoot_full"
sleep 100
release "shoot_full"
release "shoot_half"
end
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Offline reyalp

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Re: Max shutter time only 60 sec for A720
« Reply #8 on: 15 / December / 2012, 20:16:06 »
Quote from: dvip on 15 / December / 2012, 19:49:11
I can get around 30 secs using the A590IS-101b with a script like this.
The request was for > 60 seconds, which requires the "extra long exposure" support code.

Regular CHDK without extra long exposures should be able to do ~64 seconds = APEX -6 = APEX*96 -576
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Offline lapser

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Re: Max shutter time only 60 sec for A720
« Reply #9 on: 15 / December / 2012, 23:41:08 »
Quote from: reyalp on 15 / December / 2012, 20:16:06
The request was for > 60 seconds, which requires the "extra long exposure" support code.
Regular CHDK without extra long exposures should be able to do ~64 seconds = APEX -6 = APEX*96 -576
Let me see if I understand this:

There is a limit of 64 seconds in the camera firmware.

You can get  64 seconds maximum with set_tv96_direct(-576)

There is an extra long exposure patch in CHDK that removes the Canon 64 second firmware limitation by patching the machine code in the firmware that sets the limit.

Activating extra long exposure depends on the patch being entered correctly, specifically for each camera and firmware version.
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I checked my sx260 by setting long exposure over-ride to 2 minutes. I only got 64 seconds. I also get a maximum of 64 seconds with set_tv96_direct(...). But after reading this, I decided to check the G1X (ported by philmoz). The exposure lasted the full 2 minutes. It works on the G1X (thanks philmoz!)

So the patch doesn't seem to be installed correctly on the sx260. I'll check with nafraf to see if he can fix it.

I'm assuming that I can also set longer tv values on the G1X with set_tv96_direct(...) ?
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