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Change ISO on Long exposures, SX50HS

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Offline britab1967

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Change ISO on Long exposures, SX50HS
« on: 23 / September / 2015, 05:08:13 »
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Hi

I've just purchased a second hand SX50HS because I knew I could get CHDK onto it and expand its features, which is great thanks.

I was able to use on of the intervoltmeter scripts last night to take 100 25s shots of the clear sky and stack them together.

I can't see how to change the ISO level above 80 when I go above 1.2s but I have seen some photo's with ISO 200 at 15s, so I know that it can be done, I just don't know how.

Can anyone please help.

Thanks
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Offline waterwingz

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Re: Change ISO on Long exposures, SX50HS
« Reply #1 on: 23 / September / 2015, 08:32:57 »
Quote from: britab1967 on 23 / September / 2015, 05:08:13
I was able to use on of the intervoltmeter scripts last night to take 100 25s shots of the clear sky and stack them together.
You might be interested in this : Meteor Intervalometer with Dark Frame Management

Quote
I can't see how to change the ISO level above 80 when I go above 1.2s but I have seen some photo's with ISO 200 at 15s, so I know that it can be done, I just don't know how.
When all else fails, there is always RTFM : CHDK User Manual : Override ISO value

Edit : you can also manage ISO settings from within your script : set_sv96
« Last Edit: 23 / September / 2015, 09:02:42 by waterwingz »
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Offline britab1967

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Re: Change ISO on Long exposures, SX50HS
« Reply #2 on: 23 / September / 2015, 09:20:00 »
Quote from: waterwingz on 23 / September / 2015, 08:32:57

Quote
You might be interested in this : Meteor Intervalometer with Dark Frame Management

I have copied that ready to try on our next clear night.

Quote
When all else fails, there is always RTFM : CHDK User Manual : Override ISO value

Thanks, I have been reading that part of the manual but I was struggling to make sense of what it was saying. I'll have a play tonight.

Thanks for your assistance.
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Offline waterwingz

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Re: Change ISO on Long exposures, SX50HS
« Reply #3 on: 23 / September / 2015, 09:31:23 »
Quote from: britab1967 on 23 / September / 2015, 09:20:00
Thanks, I have been reading that part of the manual but I was struggling to make sense of what it was saying. I'll have a play tonight.
The values you set in the Enhanced Photo Operations meny will override the values that the Canon firmware wants to use when you take pictures.   Note that the camera firmware does not know that you have set an override, so if you override one exposure setting,  you really need to override them all if you want to control the exposure.

Taking some test pictures with different settings is probably the best way to see how this works.  Don't forget to set Disable Overrides [ No ]
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Offline britab1967

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Re: Change ISO on Long exposures, SX50HS
« Reply #4 on: 23 / September / 2015, 10:21:49 »
Quote from: waterwingz on 23 / September / 2015, 09:31:23
Quote from: britab1967 on 23 / September / 2015, 09:20:00
Thanks, I have been reading that part of the manual but I was struggling to make sense of what it was saying. I'll have a play tonight.
The values you set in the Enhanced Photo Operations meny will override the values that the Canon firmware wants to use when you take pictures.   Note that the camera firmware does not know that you have set an override, so if you override one exposure setting,  you really need to override them all if you want to control the exposure.

Taking some test pictures with different settings is probably the best way to see how this works.  Don't forget to set Disable Overrides [ No ]


Thanks waterwingz, I'll have a go with that. I can see that set-sv96 is within the script and look forward to seeing how that goes.

Thanks again.
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Offline reyalp

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Re: Change ISO on Long exposures, SX50HS
« Reply #5 on: 23 / September / 2015, 17:42:59 »
FWIW if you are using raw, there may not be much difference between shooting at higher ISO or adding exposure adjustment later in processing. How different it is may vary depending on camera, so I would definitely recommend testing before using this approach for a long sequence.
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