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ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor

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Offline Caribou007

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ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« on: 27 / November / 2013, 14:58:52 »
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As per this discussion,

http://www.dpreview.com/forums/thread/3122055#forum-post-40227068

The S100 is locked to ISO80 for long exposures and the timer is limited to 15 seconds.

At the end of the thread someone speculates this might be to avoid overheating of the CMOS sensor.

Now that CHDK Beta is available for the Powershot S100, I am looking for an update on those issues.  Whether CHDK allows for exposures at a higher ISO, for periods longer than 15 seconds, (and bulb mode).  What quality are the results?  Why did Canon create these limitations in their firmware?  And of course, is there a risk of hardware damage with long exposures at high ISO?
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Offline reyalp

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Re: ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« Reply #1 on: 27 / November / 2013, 16:32:06 »
Quote from: Caribou007 on 27 / November / 2013, 14:58:52
Now that CHDK Beta is available for the Powershot S100, I am looking for an update on those issues.  Whether CHDK allows for exposures at a higher ISO, for periods longer than 15 seconds,
Probably. The development thread is the best place to find current status http://chdk.setepontos.com/index.php?topic=7887.190
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(and bulb mode).
No, chdk does not have a bulb mode.
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Why did Canon create these limitations in their firmware?
Unknown. If you run into a Canon engineer in a bar, buy them a drink.
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  And of course, is there a risk of hardware damage with long exposures at high ISO?
Unknown. My gut feeling is that it's more likely the limits would be based on quality rather than hardware damage, but that's only a guess. I would expect they would have some sort of thermal monitoring that would panic if temperatures got to high.

You can monitor the sensor temperature with CHDK, although the thermistor used is not necessarily on the sensor itself.
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Offline waterwingz

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Re: ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« Reply #2 on: 27 / November / 2013, 16:52:42 »
Quote from: reyalp on 27 / November / 2013, 16:32:06
http://chdk.setepontos.com/index.php?topic=7887.190
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(and bulb mode).
No, chdk does not have a bulb mode.
This has come up a couple of times.  Seems like we could set Tv to some long value ( 60 seconds ) and use the USB remote to control :
Code: [Select]
call_event_proc("Mecha.Create")
 call_event_proc("OpenMechaShutter")
 call_event_proc("CloseMechaShutter")
multiple times if that was required for the desired effect.   

You'd have to wait for the whole 60 seconds for the shot to finish but you could get "Bulb" manual control that way?

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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline reyalp

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Re: ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« Reply #3 on: 27 / November / 2013, 17:15:21 »
Quote from: waterwingz on 27 / November / 2013, 16:52:42
You'd have to wait for the whole 60 seconds for the shot to finish but you could get "Bulb" manual control that way?
Might work, but you'd get all the noise of a full 60 sec exposure...
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Offline Caribou007

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Re: ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« Reply #4 on: 27 / November / 2013, 17:48:51 »
It would be nice to be able to create extreme time-lapse photography, if the opportunity arose.

Are the quality issues you referred to related to noise?

And the temperature sensor available in CHDK would be useful for thermal testing.  Are the thermal limits known? 

It's good that no one has reported actual camera damage trying anything like this.
« Last Edit: 27 / November / 2013, 17:51:48 by Caribou007 »
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Offline reyalp

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Re: ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« Reply #5 on: 27 / November / 2013, 18:21:54 »
Quote from: Caribou007 on 27 / November / 2013, 17:48:51
Are the quality issues you referred to related to noise?
Noise, dark current, amp glow

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And the temperature sensor available in CHDK would be useful for thermal testing.  Are the thermal limits known? 
No that I know of.

edit:
IMO, there is essentially no chance the ISO restriction has anything to do with thermal limits. ISO only affects the amplifier setting when the image is read out and subsequent noise reduction and other software processing applied by the firmware. It's very hard to see how this would have a significant impact on sensor temperature.

Also, essentially all Canon P&S have a factory limit of 15 sec for long exposures, so this limit isn't something new for CMOS sensors. All CHDK ports normally support up to 64 seconds, and many allow up to 2048 seconds. In the latter case, some cameras fail to capture an image before the theoretical limit, but as far as I know no one has damaged a camera doing this.

For astrophotography, stacking is usually preferable to such long exposures anyway.
« Last Edit: 27 / November / 2013, 18:36:31 by reyalp »
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Offline waterwingz

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Re: ISO lockout, exposure time limits, and the Powershot S100 CMOS sensor
« Reply #6 on: 27 / November / 2013, 18:32:55 »
Quote from: Caribou007 on 27 / November / 2013, 17:48:51
It would be nice to be able to create extreme time-lapse photography, if the opportunity arose.
From what I've seen,  images like the one you posted are created in post production by merging hundreds of individual images.  There are lots of posts on this forum about software that does that if you do a little searching.
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Ported :   A1200    SD940   G10    Powershot N    G16
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