Public Lab Research note

3-camera rig testing with with CHDK

by patcoyle | May 20, 2012 03:52 20 May 03:52 | #2144 | #2144

I flew a quick 3-camera rig test with Sutton FF16 with MK111 timer and CHDK intended to trigger Canon A490 (iR converted by Jeff Warren) and A495 (visible).

The MK111 timer and batteries were in a plastic bag slung in the center rig position. An iPhone 4s with CameraSharp app, which shoots in continuous mode and geotags photos with gps info, was flown below the bag with the timer.

There were issues. The A490 (iR) didn't shoot. Afterwards, it appeared the SDHC card hadn't clicked into place properly. In my rush, I didn't stop to check it.

The A495 shot over 700 images but they were all unusably overexposed. I didn't consciously change exposure or apply the shutter priority settings, Jeff discusses at:

Perhaps I should have. The screenshot, overexposed photo info, shows the shutter speed at 1/20th of a second. for one of the overexposed image. A few of the over 1800 iPhoto images are visible in the far right of the screen.

Suggestions are welcome.


Actually i think that dual-camera wiki section on shutter priority was Chris F's -- it's a good idea but personally I usually leave it on auto, and have gotten good results with the A495.

Whenever you fly more than one camera, you multiply the # of things that can go wrong, i guess :-( but it's great for comparing the performance of various cameras.

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Pat, Thanks for posting this. I agree with Jeff that the automatic modes in Powershots are incredibly useful for getting good results with no fretting over settings. When an A490 or A495 (and many similar Powershots) is in AUTO mode, the shutter speed, aperture, focus, white balance, and ISO are all chosen for each shot using a very smart algorithm.

Some entries in the dual camera wiki address the issue that flying cameras should have high shutter speeds all the time. CHDK can be used to lock shutter speed (e.g., at 1/800 second) and the camera will vary the aperture (this is called shutter priority, and some Powershots offer it, but not the A490 or A495). The wiki also discusses that for stitching photos together to make maps, it often makes sense (e.g., when the lighting conditions are constant) to have all photos taken with the same basic settings. That is the justification for using PROGRAM mode on the Powershots (allows you to lock ISO, white balance, and allows infinity focus mode). The combination of these two features, CHDK’s shutter priority mode and the camera’s PROGRAM mode, have the potential to get the highest quality aerial photo results out of these little cameras.

Pat, What settings did you use for the visible camera? The information you show for one photo says ISO was 400, shutter speed was 1/20 second, and aperture was f/3 (all the way open). Was the camera in PROGRAM mode or AUTO mode? I don’t quite understand how either mode could produce such overexposed images. Both of these modes are “automatic exposure” modes and will select a combination of shutter speed and aperture to give a good exposure. The fact that the aperture was all the way open suggests that something was preventing the camera from doing its job. Could a CHDK setting have been responsible for this? Can you take normal photos with camera right now? Were the ISO and exposure settings the same for all the photos or did they vary? If you have any more information about the camera or CHDK settings, maybe we can figure out how to avoid this problem.

It is real progress that your cool rig worked well, you got the whole thing off the ground under a FF16 kite, your MK111 timer worked, you got CHDK to enable remote triggering, you learned more about pre-flight checklists, and you must have a good GPS log of the flight from the iPhone. I haven't heard about many other folks making that much progress.

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Thanks Chris,

I appreciate the encouragement. I just checked and the A495 was in Program mode. I was using it with rubber band over shutter in continuous mode before. I just took a half dozen photos that look normal. I'll have to look at the CHDK settings and see if I can share them to troubleshoot it, unless I can sort it out.

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Tonight I took a few minutes and was able to get the Canon A495 triggering with the CHDK circuit and taking photos that looked reasonable, given the low light level inside the house. Earlier I had trouble. When I looked this evening, on start up, the settings for remote control were not enabled so I checked those off and then it proceeded to work. I started just by using the USB port connected to the computer to trigger it, then set up the MK 111 timer actuated circuit and it ran triggering from that. So then I started up the A490 which had worked this afternoon and both proceeded to trigger. I went out to the kitchen and shot for a few more images.

A composite of a couple pairs of synched images is at:

Just looking at them I'm wondering about the relative speeds at which the 490 in IR and 495 in visible shoot and save images.

I've set the camera times more closely. They were off by four plus minutes. Then, I'll check this out.

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