a720 Custom Auto Iso -> Shutter speed, build 50 bug? - AllBest's Builds - CHDK Forum
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a720 Custom Auto Iso -> Shutter speed, build 50 bug?

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Offline gueloh

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a720 Custom Auto Iso -> Shutter speed, build 50 bug?
« on: 06 / April / 2008, 14:58:04 »
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Hi all,

first off all thank you for the special sw which allows me a lot of more fun with my canon.

I have a problem with the new function of the build 50.  I want to use the Custom Auto Iso setting with a specific minimum Shutter speed. But this feature seems  not to work with the A720. The override of Iso works if the Minimal Shutter speed is set to auto. If I set the shutter speed to a value nothing is working, the shutter speed is not changed at all.

My problem is that the A720 camera setting is most at speed 1/60 which gives blured images if some motion is on the scene. Therefore I wanted only to force a higher minimum speed (for motion scenes).

Thanks in advance.
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Offline mkmenuts

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  • SD700 (1.01b)
Re: a720 Custom Auto Iso -> Shutter speed, build 50 bug?
« Reply #1 on: 06 / April / 2008, 15:10:36 »
Please provide some data:

1. What ISO (real + market) was used when Custom AutoISO was off?
2. What was the corresponding shutter speed?
3. Same as 1+2 when custom AutoISO was on.
4. Custom AutoISO settings you used.

mkmenuts
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Offline gueloh

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Re: a720 Custom Auto Iso -> Shutter speed, build 50 bug?
« Reply #2 on: 07 / April / 2008, 02:15:16 »
Hi mkmenuts,

I have played a little bit and found that the Iso setting is working also if I set the Minimum Shutter Speed. But the minimum Shutter is not set at all.

May be I'm expecting something wrong from the function and the settings. It was allways a little bit dark and if the minimum shutter speed will be set the images will be underexposed. So maybe it only works in a very bright environment which allow to set the Iso and aperture in a way to allow the minimum shutter speed without change the exposure of the image.

The settings in the User Factor (IS Factor) of the Custom AutoIso menu to scale the camera internal settings are only driven in the direction to slow the shutter. If someone want to force the settings to always use a more conservative setting (regarding shutter speed) it is not possible with this function. Maybe it is possible to divide by 10 the setting and allow the User Factor (IS Factor) a increasing in shutter speed (eg. setting 5 is then 0.5 and double the shutter speed).

To ansver to your question:
1. Iso 200 (real 130), shutter 1/6 s with the Custom AutoIso off
2. Iso 160 (real 99), shutter 1/6 s with the Custom AutoIso on (Minimum shutter was set to 1/500 s)
3. see above
4. Settings:

Minimal Shutter Speed: 1/500 s
User Factor: 1
IS Factor : 1
Max ISO High: 25
Max ISO Auto : 10
Min ISO Auto : 3

Thank you for your time
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Offline mkmenuts

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  • SD700 (1.01b)
Re: a720 Custom Auto Iso -> Shutter speed, build 50 bug?
« Reply #3 on: 07 / April / 2008, 03:08:09 »
Hi gueloh,

What you indicate may indeed be a bug, or (more likely) a display problem:

Your settings allow max real ISO of 100, since the original shutter was very slow to begin with custom autoiso would have wanted to increase ISO and get a faster shutter speed (closer to 1/500 if possible).

However, the ISO max you put in is LOWER than the camera suggested, and the real ISO was actually decreased to 100 (thus requiring a slower shutter. My guess is that the shutter was slowed (to around 1/5s) but due to rounding errors you did not see the effect on screen. Check the EXIF data to be sure.

The idea behind custom autoiso is to expand the range (say 75-400 market ISO) and provide more info (recommended shutter speed) to the camera to make intelligent decision by itself. Since you made the range smaller, the camera had little to do.

Also, try setting the base iso a little higher (mine is good at 5), anything lower is actually giving me worse results with slightly more noise.

Hope that helps,

mkmenuts
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Offline gueloh

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Re: a720 Custom Auto Iso -> Shutter speed, build 50 bug?
« Reply #4 on: 07 / April / 2008, 16:12:11 »
Hi all,

following the threat, I have played a little bit with the Cusom Auto Iso and I found the following behaviour:

The Minumum Shutter Speed is working if the camera exposure setpoint is settable via increasing of the Iso. Eg. Minumum Shutter Speed setting is 1/125 s.  If with  the Cusom Auto Iso Off the Iso is 100 and the shutter is 1/60 s then in Cusom Auto Iso On the shutter speed is 1/125 s with the Iso 200.

-> So the function works also with the A720, no bug detected.

=> For a further improvement of this function and for more flexibility I suggest to modify the function in the way to allow the User Facter also to become <1. This give the benefiz of increasing shutter forcing as described above in this threat. May be someone follow the suggestion.

Thank you all for the help.
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