"Loading" ISO override settings into camera - AllBest's Builds - CHDK Forum supplierdeeply

"Loading" ISO override settings into camera

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Offline e2b

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"Loading" ISO override settings into camera
« on: 29 / December / 2007, 06:35:51 »
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)?

By the way, 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).

Re: "Loading" ISO override settings into camera
« Reply #1 on: 29 / December / 2007, 10:42:52 »
Well, I registered here to say Allbest's ISO override won't work but setting custom ISO from scripts worked on earlier versions. Then I investigated a bit further and found out that it has never actually worked. :'(

I've always thought that changing ISO changes voltage/current running through CCD sensor. Correct me if I'm wrong. Higher ISO means more sensitive sensor and lower ISO less sensitive, of course. If I remember correctly, somebody warned not to burn sensor with huge ISOs when custom ISO was invented.

But I found that at least mine A610 has less sophisticated way to handle ISOs: software. Let me explain with sample shots. :)

OK, I have Powershot A610 with 1.00F firmware. I used Fingalo's build first, then Allbest's to see if it would make any difference but it didn't so I stuck with Fingalo's. ISO 50 to 400 is selected from camera's own menu, 800 to x is selected via script.

Settings were 1/13s, F4.0, manual focus and manual white balance. Changing ISO should change lightness and noise.

So here is the pictures I shot, in JPEG straight from the camera: http://theadmin.1g.fi/kuvat/Canon+HDK/Custom+ISO/

Results on JPEGs are something you would expect, but check the RAWs here: http://theadmin.1g.fi/kuvat/Canon+HDK/Custom+ISO/RAWs/

Even camera's own ISO settings will not effect RAWs. :o I'm a bit muddled here.

Re: "Loading" ISO override settings into camera
« Reply #2 on: 23 / January / 2008, 18:11:40 »
Try the -W option when using dcraw.

Re: "Loading" ISO override settings into camera
« Reply #3 on: 04 / February / 2008, 06:06:14 »
There is no such option in version 8.75 what I normally use. Newer version 8.81 had it but results didn't differ at all from older version. I guess the older version do not have automatic brightening.

However, I found out that option -4 has some effect on different ISOs but images will be dramatically darker.

I still think something else controls sensor's sensitivy than ISO.


Offline brainwash

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  • Nikon D40x & A460
Re: "Loading" ISO override settings into camera
« Reply #4 on: 07 / February / 2008, 12:04:06 »
ISO override or shutter speed override still won't work for me on an S2 IS, not even with the method you mentioned.
However, if I keep the shutter pressed, the way the 'preview' image has the correct brightness while the image seen in preview mode has the same histogram at ISO 400 or above and 1/3200 and below.


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