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Reducing the minimum exposure speed in High-speed Burst HQ mode

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Offline longtalker

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Reducing the minimum exposure speed in High-speed Burst HQ mode
« on: 10 / January / 2014, 05:39:50 »
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Hi everyone

I am using CHDK 100f-1.2.0-2246 for SX40 HS. With it, in High-speed Burst HQ mode, the minimum exposure speed that can be set is 1/8s. I would like to be able to decrease this further, at least down to 1/4, so that the AutoISO can then select a lower ISO value.

Since it appears that no further CHDK releases are planned for this camera model, I was wondering if this simple improvement is also easily changeable (by a non-specialist) in the CHDK code. I would really appreciate some assistance with doing this. Many thanks in advance!
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Offline flipper321

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #1 on: 10 / January / 2014, 06:29:29 »
Surely taking photos at 1/4 the "absolute maximum" number of shots you can take in a second is 4. With other overheads this probably drops to at most 3 shots per second which you couldn't really call "burst" mode any more?

How many shots per second do you need?
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Offline longtalker

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #2 on: 10 / January / 2014, 07:25:44 »
I see what you mean - let me explain further.

I normally use the HQ mode in low light conditions when no tripod is available, in order to take several shots (the SX40 takes series of 8 pics), the least blurred of which I then keep later on. I find that, at full wide lens, and with the camera firmly held, 1/8s gives me a rate of non-blurred pics of about 70%, so I figured I can "afford" to drop the speed down to 1/4s, which will probably halve the percentage of unblurred shots, but which also uses a better ISO.
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Offline philmoz

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #3 on: 10 / January / 2014, 07:30:03 »
Quote from: longtalker on 10 / January / 2014, 07:25:44
I see what you mean - let me explain further.

I normally use the HQ mode in low light conditions when no tripod is available, in order to take several shots (the SX40 takes series of 8 pics), the least blurred of which I then keep later on. I find that, at full wide lens, and with the camera firmly held, 1/8s gives me a rate of non-blurred pics of about 70%, so I figured I can "afford" to drop the speed down to 1/4s, which will probably halve the percentage of unblurred shots, but which also uses a better ISO.

Using the CHDK overrides, you can manually override the shutter, aperture and ISO to whatever values you want - even in HQ burst mode.

Phil.
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Offline longtalker

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #4 on: 10 / January / 2014, 07:41:39 »
I know that I could override all these parameters manually, but it is very convenient to use the HQ mode with AutoISO, because it selects the lowest possible ISO given the constraint of your slowest acceptable speed - the only problem, as I was saying, is that it sets a lower limit for exposure time of 1/8s, no slower.

I could, of course, just use the continuous shooting mode of the P wheel-position, and set exposure time and ISO manually, however this not only takes more time but also the entire set of 8 pics takes longer to shoot than in HQ mode.

Is there a way to have a few slower options in the minimum exposure speed menu entry, such that it doesn't stop at 1/8 but continues down to e.g. 1/6, 1/4 etc? Many thanks.
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Online reyalp

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #5 on: 11 / January / 2014, 00:39:54 »
Quote from: longtalker on 10 / January / 2014, 05:39:50
Since it appears that no further CHDK releases are planned for this camera model
I don't understand this. When CHDK is updated, it is updated for all supported cameras.

CHDK releases aren't really planned though, so that part is right :haha

If you are talking about CHDK "custom auto ISO" being limited to 1/8th, that could certainly be changed to allow lower values. Seems like a reasonable request to me.
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Offline waterwingz

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #6 on: 11 / January / 2014, 01:02:34 »
Quote from: reyalp on 11 / January / 2014, 00:39:54
If you are talking about CHDK "custom auto ISO" being limited to 1/8th, that could certainly be changed to allow lower values. Seems like a reasonable request to me.
From core/autoiso.c

Code: [Select]
static const int shutter1_values[] = { 0, 8, 15, 30, 60, 125, 250, 500, 1000 };
But then if we are going to look at AutoISO. perhaps making it aware of the camera's Av setting and ND filter setting (if  use by the Canon f/w) might also be a good idea?
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline longtalker

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #7 on: 11 / January / 2014, 05:20:58 »
Quote
I don't understand this. When CHDK is updated, it is updated for all supported cameras.

Oh I see - I thought that CHDK updates are model-specific.

Quote
From core/autoiso.c
Code:
static const int shutter1_values[] = { 0, 8, 15, 30, 60, 125, 250, 500, 1000 };

So I take it it's enough to e.g. simply add a 4 in between the 0 and the 8, in order to have 1/4s as the smallest value in the "Minimal shutter speed" list? And then is it enough to just save the file with this change, or is some re-compilation needed? If so, how is it done?...

The problem is, though, that I haven't found any CORE folder inside my CHDK folder. I searched for a file named autoiso.c on the entire SD card, and none was found.

Thanks again for your help.
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Offline msl

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #8 on: 11 / January / 2014, 05:35:34 »
This is not a part of the CHDK package for the sd card. It's an excerpt from the CHDK source code.

You (or another person with skill) must change the source code and compile a new CHDK version for your camera.

msl
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Offline waterwingz

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Re: Reducing the minimum exposure speed in High-speed Burst HQ mode
« Reply #9 on: 11 / January / 2014, 11:22:55 »
Quote from: msl on 11 / January / 2014, 05:35:34
This is not a part of the CHDK package for the sd card. It's an excerpt from the CHDK source code.
You (or another person with skill) must change the source code and compile a new CHDK version for your camera.
I've attached a build for your camera with the changes made.  It's based on CHDK 1.3.0 but you will likely not notice any differences.   SD Card lock booting only - let me know if you need to use the firmware update method and I'll see what I can find.

If this works for you,  I'll go back and do the other clean-up that's been on my list for a while (handling aperture and ND filter for cameras that have those - the current code ignores them).

Patch file attached for reference as well.


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