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Battery saving and exposure questions for aerial timelapse

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Offline guijemont

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Battery saving and exposure questions for aerial timelapse
« on: 04 / June / 2011, 06:30:16 »
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Hi fellow CHDKers!

A friend and I are on a crazy project, attempting to do timelapse photography from a helium-filled balloon. For the curious, the project is explained there: http://balloonfreaks.mooo.com/blog/2011/05/09/the-balloon-project/ .

In that context, we think of using CHDK on a Powershot SX110 IS, and there are two issues that we keep on wondering about.

1/ Low Power Mode?

I did some battery consumption measurements, the process I used is described here: http://balloonfreaks.mooo.com/blog/2011/05/16/measuring-power-consumption-the-macgyver-way/

I also ran measurements while running CHDK, and without doing anything, or while running a simple intervalometer, I had the following issues:
 - I could not get the screen to turn off
 - Power consumption was always at the maximum (~1.5W)
I also tried to plug in the video out cable; it did turn the screen off, but without changing the power consumption (still around 1.5W).
Without CHDK, after a given period of time without doing anything, the camera automatically gets to a lower power mode (around 0.4W) with the screen turned off: is there a way to get to that low power mode with CHDK? Note that I don't mind if this involves modifications of CHDK itself, if I am given directions on where to look (I don't know CHDK's code base).

2/ Automatic Exposure while keeping a fast shutter speed

Since light conditions will evolve while our camera is up taking pictures, we want the exposure parameters to adapt automatically to the light. But since the camera will be attached to a relatively shaky balloon, we want to avoid long exposure times that would just result in useless blurry pictures, and would rather play with extreme ISO and aperture size settings. Any suggestions on how to do that? Is there already a script out there that can do it?

Thanks for reading me, and even more thanks if you can help me :)

TL;DR:
 - how can I get in low power mode?
 - how can I have the exposure automatically set as right as possible while keeping a fast shutter speed?
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Offline reyalp

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #1 on: 05 / June / 2011, 01:11:59 »
The "miscellaneous stuff"->Disable LCD off option sounds like what you are looking for.

If your camera has a DISP button, you can also click this from CHDK script.

For exposure, you can script your own autoexposure and set whatever limits you want.
The camera operates in APEX*96 values (see http://dougkerr.net/Pumpkin/#APEX )  so the get/set_*96 functions all work in these values. Exposure related propcases ( http://chdk.wikia.com/wiki/Propertycase ) also use these values. So you can take Bv96 and shuffle the Tv, Av, and Sv around however you want

fbonomi already did this quite successfully with a balloon, you might want to check out his stuff: http://www.francescobonomi.it/photo-balloon

You can find some more posts from other balloon projects if you search the forum. Here's one http://chdk.setepontos.com/index.php?topic=5286.0
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Offline Microfunguy

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #2 on: 05 / June / 2011, 06:17:33 »
Quote from: guijemont on 04 / June / 2011, 06:30:16
- how can I have the exposure automatically set as right as possible while keeping a fast shutter speed?

I am working on new uBasic commands especially for balloon photography.
Someone with a balloon (in Las Vegas) is testing the first new command today.

It is 'shoot_fast'.

Quite simply, it forces the shutter speed to be far faster than what the camera tries to set.
If it succeeds, it returns the value '1'.
If it fails, no photo is taken and it returns the value '0'.
In a script, if many '0' s are being returned you could decide to increase the ISO.

'shoot_movie_for' captures a movie clip of defined length.

'earth_exposure' will try to determine what the correct exposure for the Earth is, ignoring readings of the sun or black space.


If you wish to test these features, please contact me.
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Offline guijemont

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #3 on: 07 / June / 2011, 15:37:06 »
Quote from: reyalp on 05 / June / 2011, 01:11:59
The "miscellaneous stuff"->Disable LCD off option sounds like what you are looking for.

If your camera has a DISP button, you can also click this from CHDK script.
Will try to play with that while measuring power consumption, thanks for the tip! Not sure how this escaped me.

Quote from: reyalp on 05 / June / 2011, 01:11:59
For exposure, you can script your own autoexposure and set whatever limits you want.
The camera operates in APEX*96 values (see http://dougkerr.net/Pumpkin/#APEX )  so the get/set_*96 functions all work in these values. Exposure related propcases ( http://chdk.wikia.com/wiki/Propertycase ) also use these values. So you can take Bv96 and shuffle the Tv, Av, and Sv around however you want

fbonomi already did this quite successfully with a balloon, you might want to check out his stuff: http://www.francescobonomi.it/photo-balloon

You can find some more posts from other balloon projects if you search the forum. Here's one http://chdk.setepontos.com/index.php?topic=5286.0

Interesting, will have a look at all these pointers. Thanks.
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Offline guijemont

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #4 on: 07 / June / 2011, 15:45:19 »
Quote from: Microfunguy on 05 / June / 2011, 06:17:33
Quote from: guijemont on 04 / June / 2011, 06:30:16
- how can I have the exposure automatically set as right as possible while keeping a fast shutter speed?

I am working on new uBasic commands especially for balloon photography.
Someone with a balloon (in Las Vegas) is testing the first new command today.

It is 'shoot_fast'.

Quite simply, it forces the shutter speed to be far faster than what the camera tries to set.
If it succeeds, it returns the value '1'.
If it fails, no photo is taken and it returns the value '0'.
In a script, if many '0' s are being returned you could decide to increase the ISO.

That's what I need!
Quote
'shoot_movie_for' captures a movie clip of defined length.

'earth_exposure' will try to determine what the correct exposure for the Earth is, ignoring readings of the sun or black space.
This might not be very useful to our project, since the balloon will be tethered, and won't go above 100m of altitude. Also, we will arrange for the camera to point in the direction of the tether, so I guess the sun (or even the sky) should rarely appear, if at all.
Quote
If you wish to test these features, please contact me.
Yes please! If you want help in trying to develop them, that would be a good opportunity for me to get to speed in proper CHDK hacking. So far, all I did was svn checkout the repo.
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Offline andrewhazelden

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #5 on: 07 / June / 2011, 23:47:46 »
If you want really long battery run-time for the your Powershot SX110 IS camera you could try modding the Canon AC Adapter Kit ACK800. You could cut down the cord part with the DC barrel connector and hook it to a larger capacity external battery through a voltage regulator circuit. The ACK800 outputs approx. 3.15VDC at 2A.

Amazon sells it for about $38.

eBay has clones of it for about $19 including shipping.
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Offline fbonomi

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #6 on: 17 / June / 2011, 11:46:14 »
If you are interested, the camera is able to self-measure the batteries' voltage (not directly the consumption) and you can read that is a script (you can read it in a lua script, I don't know if there's a uBasic command for that)

For example, this is the plot of voltage decreasing during the 2008 balloon flight over Florida

the large "holes" in voltage are the moments when the camera was shooting videos.

As for the "fast exposure" problem, I went into all those problems because I was fliying an Ixus 80 (an iris-less camera with very limited settings). Your 110 has a much larger set of capabilites, and it might be worth exploring them for a simpler but perhaps acceptable result.

For example, if you set ISO to a high-ish value (e.g. 200), and go in Aperture priority, forcing the camera to keep the iris as open as possible, you are somehow suggesting the cameera to shoot as fast as possible.

I know it's not exactly what you are looking for, but being SO much easier to setup it might be worth the effort to explore that.

Also, if you want to do a time-lapse (i.e. mount the photos into a movie) you really need to think about some way of stabilizing the balloon, keeping its orientation and position somehow constant, in order to be able to have a video that looks like a video, not random photos.

For example, a 3-wire tethering system could help ...
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Offline guijemont

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #7 on: 19 / June / 2011, 08:20:54 »
Quote from: andrewhazelden on 07 / June / 2011, 23:47:46
If you want really long battery run-time for the your Powershot SX110 IS camera you could try modding the Canon AC Adapter Kit ACK800. You could cut down the cord part with the DC barrel connector and hook it to a larger capacity external battery through a voltage regulator circuit. The ACK800 outputs approx. 3.15VDC at 2A.

Amazon sells it for about $38.

eBay has clones of it for about $19 including shipping.
Yeah, we're thinking of doing that, but might be a bit short on time for that option, since D-Day is in less than two weeks now... We'll see what we can find quickly.
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Offline guijemont

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Re: Battery saving and exposure questions for aerial timelapse
« Reply #8 on: 19 / June / 2011, 10:39:43 »
Quote from: fbonomi on 17 / June / 2011, 11:46:14
If you are interested, the camera is able to self-measure the batteries' voltage (not directly the consumption) and you can read that is a script (you can read it in a lua script, I don't know if there's a uBasic command for that)

For example, this is the plot of voltage decreasing during the 2008 balloon flight over Florida

the large "holes" in voltage are the moments when the camera was shooting videos.

Looks interesting for monitoring, but I'm not sure it is good to compare the power consumption of different modes.

Quote
As for the "fast exposure" problem, I went into all those problems because I was fliying an Ixus 80 (an iris-less camera with very limited settings). Your 110 has a much larger set of capabilites, and it might be worth exploring them for a simpler but perhaps acceptable result.

For example, if you set ISO to a high-ish value (e.g. 200), and go in Aperture priority, forcing the camera to keep the iris as open as possible, you are somehow suggesting the cameera to shoot as fast as possible.

I know it's not exactly what you are looking for, but being SO much easier to setup it might be worth the effort to explore that.
I might try to play with that kind of idea. Though I feel I will have to make ISO evolve as well, since I want to try and take pictures both during day and night.

Quote
Also, if you want to do a time-lapse (i.e. mount the photos into a movie) you really need to think about some way of stabilizing the balloon, keeping its orientation and position somehow constant, in order to be able to have a video that looks like a video, not random photos.

For example, a 3-wire tethering system could help ...
Right now, I'm more looking into solutions to do that kind of "stabilisation" on post-processing. Playing a bit with OpenCV, i already have some interesting results (but still quite some work to do).
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