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CHDK(allbest) ISO Overide Question?

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CHDK(allbest) ISO Overide Question?
« on: 29 / January / 2008, 04:08:16 »
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Im not sure if the numbers im seeing are correct, but as the pictures looks it seems to be that way.

I jacked the ISO up to 800, and a value factor of 100 and I ended up with 19,000 ot 22,000 ISO's and the picture was so grainy you can barly make out what it looks like, the good thing with this is you can take a 1/30 pic in pitch dark without a tripod, almost like night vision

And then I made ISO 1 and value factor 1 and ended up with ISO's around 15 , the picture is CRISP AND CLEAR!!!

I checked ExifTool, ExifApp, PhotoStudio, and Picasa and they all said my ISO's were all around those numbers.

My main question is are they ""REALLY THOSE NUMBERS""??
if so those guys did a great job on allbest!!!!

Re: CHDK(allbest) ISO Overide Question?
« Reply #1 on: 30 / January / 2008, 20:51:27 »
Nobody Knows????? Someone has too

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Offline e2b

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Re: CHDK(allbest) ISO Overide Question?
« Reply #2 on: 31 / January / 2008, 07:14:20 »
Regarding values reported in Exif data:

In case you might miss it in the general developer's help section. I just tweaked an existing EXIF patcher to now also read the new special shutter-speeds, ISOs and f-numbers when using any of the builds of CHDK that can do these things. It puts these override values into the standard EXIF locations so that all your programs can see them as regular EXIF values.

See this thread for further info and to download your very own copy.

When I tested ISO override with Allbest v 12 and v15 on an A610 and an S3 (as described below) I found that the effective ISO override range was relatively small.

...  the method I used to check the ISO value was to take pictures of a dark blue piece of cardboard in indirect skylight. The histogram for this set-up is a single narrow peak only about 10% of the width of the whole histogram. By changing the exposure settings the peak can be placed anywhere on the histogram. Judging from the shifts in the peak position when the overridden ISO value is changed (with fixed exposure time and aperture) the ISO range for the A610 appears to be from about 30 to 600 (the marked values are 50 to 500). For the S3, the available ISO values appear to vary from about 50 to about 1000 (marked values are 80 to 800).

I wasn't concerned with what ISO value was reported - I was just interested in using the shift of the narrow-peak histogram to judge the effective change in exposure.


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Offline PS

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Re: CHDK(allbest) ISO Overide Question?
« Reply #3 on: 31 / January / 2008, 16:03:22 »


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Offline a710is

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Re: CHDK(allbest) ISO Overide Question?
« Reply #4 on: 31 / January / 2008, 16:28:45 »
I could never use the ISO override to get extreme values but I've just noticed something which might help the developers.
when I set the override and take a pic, if I keep the button pressed after taking the pic I get the preview of the photo that's recorded and it doesn't seem to want to go under ISO80 or over ISO800 however I just noticed that when I release the shutter I get a preview of how I would've wanted it to be (the brightness is proportional to the values I have set whether it's 1 or 1600 or more).
so the build basically overrides the ISO limits when the shutter is released, not when it's pressed. the pictures are saved when the shutter is pressed.
there is probably a bug on the A710 CHDK but maybe someone can fix it.
« Last Edit: 31 / January / 2008, 16:39:15 by a710is »

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Offline e2b

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Re: CHDK(allbest) ISO Overide Question?
« Reply #5 on: 31 / January / 2008, 21:43:53 »
I am wondering if what I described in the first part of the post I referred to above might be another variation on the the behaviour you have observed with the A710.

I have been exploring the way the ISO override (in AllBest's v 12 and v15) works on the A610 and S3, using the M (manual) mode setting. In the course of these tests I have come across some behaviour that I have not seen mentioned in other posts.

In certain circumstances the overriden ISO value applies, but in other cases the picture is taken with the ISO value set on the camera, and in other cases the ISO value appears to be the highest that the camera is capable of using (that is, it is not the ISO value set on the camera, nor the overridden ISO value specified in the CHDK menu). This commonly happens when the shutter button is given a 'full press', instead of first giving a 'half press', before completing the button-press.

There is a pattern to this behaviour, but instead of trying to remember the pattern, the safest way to be sure of using the specified (overridden) ISO seems to be to "load" the override ISO into the camera.

For the S3 I found that the following procedure "loads" the overridden ISO value:
1. 'Half press' the shutter button for about half-a-second. The histogram display shows that adjustments are being made.
2. Let the shutter button up again, without making an exposure.
3. 'Half press' the shutter button again for about half-a-second. The histogram display again shows that an adjustment is being made.
After this has been done, the camera will use the overriden ISO value, even if the shutter button is given a rapid 'full press'.

For the A610, just giving the shutter button a half-second 'half press' appears to "load" the overridden ISO value.

Maybe there is an easier way - has anyone had similar experiences with these cameras (or other cameras)?

I concluded that ISO override is interesting, but not not very useful :)
« Last Edit: 31 / January / 2008, 21:48:45 by e2b »

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Offline emu

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Re: CHDK(allbest) ISO Overide Question?
« Reply #6 on: 09 / February / 2008, 19:16:34 »
I jacked the ISO up to 800, and a value factor of 100 and I ended up with 19,000 ot 22,000 ISO's and the picture was so grainy you can barly make out what it looks like, the good thing with this is you can take a 1/30 pic in pitch dark without a tripod, almost like night vision

And then I made ISO 1 and value factor 1 and ended up with ISO's around 15 , the picture is CRISP AND CLEAR!!!
could you upload those pics somerwhere  please?

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Offline Tal360ca

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SAME ON MY SD1000
« Reply #7 on: 24 / February / 2008, 13:29:02 »
The same problem is with my camers. Weird, Isn't it?


 

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