Public Lab Research note

Bayou Bienvenue mapping: out of focus

by eustatic | July 30, 2012 13:45 30 Jul 13:45 | #3026 | #3026

last week, Scott Eustis, Scott Anderson, India Bush, Raynesha Jordan, and Aaliyah Marrero, in coordination with Eric Kugler of Common Ground relief, got in the canoe and paddled the ghost forest of the Bienvenue triangle. This was part of an instructional mapping exercise.

The area was once a swamp, but has subsided. Many dead stumps of cypress remain. Counting and locating these was to be part of a larger exercise, mapping Caffin Ave from wetland to the River, including the existing wetlands before an ongoing restoration project is completed.

Some instructions are learned the hard way. Embarrassingly, the camera was out of focus for those shots taken.

Posted as a reminder to make sure the A495 is auto-focused on the horizon before the launch.


Sorry to hear about the out of focus shots. I have finished more than one KAP flight only to learn that the camera was focused at 12 feet. This is a very important thing for people to know about. I guess you triggered the A495 by holding down the shutter button with a rubber band while the camera was in continuous mode. I have never tried this and was surprised to learn that when this technique is used, all of the photos are taken with the camera settings that were used for the very first photo. So when the rubber band is first put in place, the camera must be pointed at a scene similar in distance and brightness to all of the subsequent photos. Not only is the focus setting of the first photo applied to all subsequent photos, but also the shutter speed and aperture of the first photo is used. So this moment is wildly critical and usually happens just when the kite or balloon is trying to pull the camera into the air.

In order to use continuous mode on the Canon A495 and similar Powershots, the camera must be in “program” mode. While in program mode, the A495 has three focus modes: macro, normal, and infinity. I am not sure what infinity mode does, but I think it prevents the camera from searching closer than about nine feet to find focus. That might help a little at the critical rubber-banding moment.

For those wanting more control over the quality of aerial photos taken with a Powershot, it is available if CHDK is used. CHDK is easy to install on an SD card, and there is a step-by-step video at the PLOTS infrared camera tool wiki. When CHDK is used instead of a rubber band, three things can happen very differently:

1) CHDK comes with an intervalometer script that allows a photo to be taken at any interval. I have found that a photo every 8-12 seconds is plenty when the lofted camera is being dragged around by walking or paddling. This eliminates lots of wasteful duplicates (and no rubber band is needed, and the camera is not shooting in continuous mode).

2) CHDK allows the shutter speed to be locked (e.g., at 1/800 second), but the camera’s automatic exposure system continues to adjust the aperture for each shot to get a proper exposure. This high shutter speed typically eliminates motion blur in most of the photos. When it is not sunny, a slower shutter speed or higher ISO is required.

3) Because the camera is not shooting in continuous mode, settings are not locked for all photos, so the camera has to focus each shot (the A495 does not have manual focus). I always use the “infinity” focus mode which seems to help the camera focus when the scene is low contrast (like water).

CHDK is not as easy to use as a rubber band and it can introduce new critical moments which can ruin your day, but it has the potential to produce consistently better photos.

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