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SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100

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Offline longtalker

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Hello everyone,

Of all the enhancements that CHDK brings to my SX40, the ability to "de-dumb" the High Speed HQ Burst mode is my favourite, because otherwise the camera selects high ISO values even when there's enough light to use ISO100, thus giving you fast burst but low IQ.

The problem is that one cannot just override the ISO value to e.g. ISO100, because then the camera recommends an exposure based on the ISO that it would have wanted to use. Therefore, what I currently do is to override the AutoISO instead, with Min ISO=100, Max ISO Auto=100 and Max ISO HI=200 (this is the lowest possible value that can be selected). In this configuration, however, the camera always selects an Auto ISO of 160 (which probably corresponds to a "market"/Canon value of about ISO200), and never selects ISO100, even in full sunlight. Does anyone know how to fix that?

My other question is: is it possible to use CHDK so that the 3 auto bracketing (AEB) shots are taken at high speed (the kind of speed that High Speed HQ mode gives you, rather than any other mode)? Unfortunately it seems that AEB is not available in the High Speed Burst HQ Mode...

Many thanks in advance for any help!

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Offline longtalker

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #1 on: 06 / March / 2012, 17:32:19 »
Still haven't found an answer to that one, I'd really appreciate any help, many thanks in advance!

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Offline fe50

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #2 on: 07 / March / 2012, 01:24:37 »
My other question is: is it possible to use CHDK so that the 3 auto bracketing (AEB) shots are taken at high speed (the kind of speed that High Speed HQ mode gives you, rather than any other mode)? Unfortunately it seems that AEB is not available in the High Speed Burst HQ Mode...
CHDK's "Bracketing in continuous mode" feature should work in all modes, also in HQ...

* http://chdk.setepontos.com/index.php?topic=5691.msg82412#msg82412

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Offline longtalker

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #3 on: 07 / March / 2012, 05:35:39 »
Thanks! I will try that, hopefully pressing the shutter will take the 3 AEB pics in rapid succession, given that the camera is in HQ mode.
EDIT: using the "Bracketing in continuous mode" feature (with Tv +-1/3EV) in HQ mode takes all pictures with the same exposure unfortunately - it's only in mode P that the different pictures in a burst are taken with different exposure parameters.

Are you also able to help with my first question (taking burst pictures at autoISO=100 rather than autoISO=160, in HQ mode)?

Thanks again, really appreciate the help!
« Last Edit: 07 / March / 2012, 16:23:16 by longtalker »


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Offline reyalp

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #4 on: 09 / March / 2012, 17:17:08 »
Therefore, what I currently do is to override the AutoISO instead, with Min ISO=100, Max ISO Auto=100 and Max ISO HI=200 (this is the lowest possible value that can be selected). In this configuration, however, the camera always selects an Auto ISO of 160 (which probably corresponds to a "market"/Canon value of about ISO200)
I think this is a mistake. CHDK overrides, including auto ISO work in "real" ISO values. If CHDK sets a "real" ISO of 100, the "market" ISO, (as displayed in the UI and recorded in EXIF if your port records override values correctly) will be around 160. To get a lower value, set a lower Min ISO value.
Don't forget what the H stands for.

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Offline philmoz

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #5 on: 09 / March / 2012, 18:40:28 »
Thanks! I will try that, hopefully pressing the shutter will take the 3 AEB pics in rapid succession, given that the camera is in HQ mode.
EDIT: using the "Bracketing in continuous mode" feature (with Tv +-1/3EV) in HQ mode takes all pictures with the same exposure unfortunately - it's only in mode P that the different pictures in a burst are taken with different exposure parameters.

Are you also able to help with my first question (taking burst pictures at autoISO=100 rather than autoISO=160, in HQ mode)?

Thanks again, really appreciate the help!

The camera does not recalculate exposure between shots in HQ burst mode, and it does not appear to re-check the property values that are modified by the CHDK bracketing code.

So basically bracketing does not work at all in HQ burst mode on the SX40, sorry.

The market base ISO for the SX40 is 200 (was 100 on earlier cameras). This may have something to do with the auto ISO values you are seeing, haven't looked that closely at the code to see if it can be changed.

Phil.
CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)

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Offline longtalker

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #6 on: 11 / March / 2012, 08:06:31 »
Thanks Phil. Actually, it's really interesting, because I *was* able to get bracketing to work in HQ continuous mode, both for subject distance (MF) as well as for exposure, which is great! The latter, however, only seems to work reliably when varying the aperture rather than the exposure time. In the EXIF, all 8 pictures seem to have the same exposure parameters, which is probably due to the camera writing the same values for all 8 pictures, as they wouldn't normally have different exposure parameters.

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Offline philmoz

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #7 on: 11 / March / 2012, 22:06:41 »
Thanks Phil. Actually, it's really interesting, because I *was* able to get bracketing to work in HQ continuous mode, both for subject distance (MF) as well as for exposure, which is great! The latter, however, only seems to work reliably when varying the aperture rather than the exposure time. In the EXIF, all 8 pictures seem to have the same exposure parameters, which is probably due to the camera writing the same values for all 8 pictures, as they wouldn't normally have different exposure parameters.

Thanks for the update, just retested on mine and it does work for aperture and SD - potentially very useful for HDR and macro shots.

Phil.
CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)


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Offline longtalker

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Re: SX40: Using the High Speed Burst HQ mode for AEB, & at ISO 100
« Reply #8 on: 12 / March / 2012, 05:57:12 »
Very useful indeed! I love CHDK!

 

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