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ISO advice

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Offline pigeonhill

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ISO advice
« on: 15 / February / 2019, 16:30:37 »
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Hope someone can help.


I’m simply trying to set the ISO to 100, 400 and 1600 in my script.


I’ve tried all three script calls but none of them approach the above values.


Am I missing something? Can we not set explicit/classic ISO values like those above.


Cheers


Garry
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Offline reyalp

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Re: ISO advice
« Reply #1 on: 15 / February / 2019, 16:42:42 »
Which camera, and what functions are you using?

If you want to do the equivalent of setting manual ISO in the canon UI, you can set propcase ISO_MODE to the specific UI value (e.g. 100, 200). ISO_MODE should be set before half press, and will remain in effect until you change ISO in the Canon UI, use CHDK ISO overrides, reboot (I think) etc.

Setting values that are not accessible in the UI may not have the desired results, so for example on G7x, you should not set 100, since the minimum is 125,  and you should not set 234 because that's not one of the standard steps.

To set an arbitrary ISO, you should use the set_sv96 function. This takes an APEX96 "real" value, so to set the equivalent of a UI ISO, you should do something like
Code: [Select]
set_sv96(sv96_market_to_real(iso_to_sv96(125)))
This takes effect only for the next shot, *but* the camera will effectively left in AUTO ISO for subsequent shots. You can save/restore propcase ISO_MODE before/after using it if you want to preserve whatever the previous state was.

set_sv96 can generally be used outside or inside half press though the latter may have issues in some cases.

edit:
Note that while you can set values outside the canon UI range with set_sv96, they will like not give you significantly expanded ISO range, and might crash.
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Offline pigeonhill

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Re: ISO advice
« Reply #2 on: 15 / February / 2019, 16:48:24 »
@reyalp


Many, many thanks for your ultra quick response. It is great info and will help me a lot.


Cheers


Garry



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Offline pigeonhill

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Re: ISO advice
« Reply #3 on: 15 / February / 2019, 16:57:53 »
@reyalp

Just to say that your hint appears to work on my G1X. Here is the code snipet:
Code: [Select]
if j == 3 then
        local iso = get_sv96()
        set_sv96(sv96_market_to_real(iso_to_sv96(100)))
        shoot()
        set_sv96(sv96_market_to_real(iso_to_sv96(800)))
        shoot()
        set_sv96(sv96_market_to_real(iso_to_sv96(1600)))
        shoot()
        set_sv96(iso)
    else
Finally, are you saying the above would 'fail' on, say, a G7X, ie no ISO 100 accessible.
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Offline reyalp

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Re: ISO advice
« Reply #4 on: 15 / February / 2019, 17:09:32 »
Quote from: pigeonhill on 15 / February / 2019, 16:57:53
Finally, are you saying the above would 'fail' on, say, a G7X, ie no ISO 100 accessible.
You can probably set 100, but the actual exposure will probably be something like 110... or it might crash, though we do try to restrict ranges known to crash.

If you want to test usable ISO range, you can use the isoinc script I wrote: https://chdk.setepontos.com/index.php?topic=12165.0 (latest version on the last page)

edit:
Also, just FYI, G1x has unique quirks related to ISO https://chdk.setepontos.com/index.php?topic=13191.0
« Last Edit: 15 / February / 2019, 17:17:49 by reyalp »
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