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Posts Tagged ‘GentLED’

Kiholo Bay Inlet

Posted by Tom Benedict on 07/06/2009

Worldwide KAP Week is over for 2009, but KAP is a year-round activity for me.  The past six months we’ve been plagued with volcanic gasses coming out of the Halemaumau Crater on Kilauea, but a few days ago the tradewinds came back, blew the volcanic plume out to sea, and for the weekend, at least, our sweeping panoramic views were back.  It was a tough call whether to do ground-based photography or to fly a camera, but in the end the kites won.

Unfortunately because we’d had such uncharacteristic wind for such an uncharacteristically long time, the wind models I rely on to decide where to fly were reporting bogus information.  The models predicted 6-8 knot kona winds at my house, whereas I could look outside and clearly see it was blowing 10-12 knot tradewinds.  When technology fails, the eyeball prevails.  I packed my gear and my son and drove down to the coast.

In addition to editing the book for Worldwide KAP Week 2009 and starting work for a book of my own, I’ve also started making some KAP posters.  But in order to print them at the size I would like, I’ve been faced with the resolution limit of my photography.  I’ve been getting my posters printed using the El-Co Color Labs Internet Special.  They use a Durst Theta printer, and print on Fuji papers using Fuji chemistry.  A quick word about digital printing:  There are two basic ways to make a digital print.  One is to use a transfered medium, like a dye sublimation process, or an inkjet process.  The other is to take a photographic paper and to expose it to light.  Each has its own advantages, but I like the second for the bulk of the photo work I do.  The Durst Theta printers expose photographic paper to light, and then develop the paper the same way a film-based photo lab would.  The result truly is a photographic print.

But resolution is the key.  The Durst Theta can print at up to 254 dpi.  At 24×30″ that’s an image 6096×7620 pixels, or a 44 megapixel image.  I’ve made prints at resolutions as low as 150 dpi on a Durst Theta printer, but I prefer not to go below 200 dpi.  For this set of posters 200 dpi is my lowest resolution.  This is still a huge image, and the bulk of the pictures I have on file simply aren’t up to the task.

This has driven me to re-visit sites where I’ve been able to make good photos, but without the resolution necessary to print.  So I was overjoyed when driving down the coast to find that the wind at Kiholo Bay was a nice 7.4 knot on-shore.  Perfect.

Kiholo Bay has a fantastic reef, and is an outstanding place to do snorkeling and SCUBA.  There’s a good dirt road that will take you all the way to the water’s edge, so there’s no great hardship to get there.  It’s a popular spot, but not so overcrowded as, say, Hapuna Beach.  But if you’re willing to go a little further and work a little harder, Kiholo Bay has a feature that’s not to be found anywhere else in the Islands: the inlet at Kiholo Bay.

Wainanali`i Pond

There are two approaches to the inlet.  One is around the water’s edge from the park at Kiholo Bay.  The other is to park off the side of the highway, a little more than half a mile away.  The walk across the lava is not bad, but it’s not a traditional trail.  The “trail” is a series of paint splotches on the rocks to tell you vaguely where to go.  But the ground is rough lava.  It’s more than possible to get hurt, and this time I did.  I twisted my ankle.

A Study in Salinity

What makes the inlet special is that it’s a relatively deep patch of water with a very shallow mouth connecting it to the sea.  The level of the pond rises and falls with the tides, but tidal flow causes very little mixing of the water inside the pond.  As a result it is highly stratified, with seawater salinity levels at the surface, and high salinity levels further down.  The salinity at the bottom of the pond can easily be double that at the surface.  Select euryhaline organisms inhabit the higher salinity levels, turning the water its characteristic opaque aquamarine blue, whereas the surface water is all crystal clear.

The shallow mouth and opaque water in the inlet make it the perfect habitat for honu, or Pacific green sea turtles.  The pond is relatively free of predators, so the honu are able to forage in some measure of peace and security.

Flying Solo

The honu swim in the high salinity waters at the bottom of the pond, moving like phantoms through mist.  Every once in a while one will come to the surface for air, slipping into the clear waters above and then descending once more into the obscuring depths.

The arm of land that cuts the inlet off from the sea is mostly composed of rounded rocks rather than the hard lava flow that makes up the opposite shore.  This provides a good spot for honu to come up out of the water to rest and sun themselves.  Honu are protected by law, so people are not supposed to approach or touch them. A 20′ minimum distance is required, but I try to maintain at least 40′ between me and a honu on land.  With the low traffic of humans at the inlet, and the lack of predators, this provides a wonderful spot to study them.

A Study in Turtles

Hawaii Preparatory Academy (HPA) maintains a remote observation station at the Kiholo Bay Inlet.  The station has had some upgrades since my last visit, and now sports three PV panels, a fixed mount infrared camera, a fixed mount visible camera, a pan tilt zoom camera, and an RF link back to Waimea.  To learn more about this installation and the research program, you can visit:  HPA/NOAA Sea Turtle Research and Conservation Program.

But for me, the Kiholo Bay Inlet is simply a beautiful place that I have the privilege of being able to see and photograph.  It’s not the easiest place to get to, and there’s no fresh water or shade to speak of.  But Kiholo Bay isn’t here for us, it’s here for the honu.  I just feel fortunate I get to visit from time to time.



(Note:  I have been calling the Kiholo Bay Inlet by the wrong name: Wainanalii Pond.  This is how it is commonly labeled on maps, hence my mistake.  But during a conversation with Bobby Camara, he pointed out that the village of Wainanalii is a two hour canoe ride to the north of Kiholo Bay, and that it was destroyed by the same lava flow that created the inlet.)


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Mechanics of KAP

Posted by Tom Benedict on 28/05/2009

On the off-chance that my previous post sparked some interest in doing kite aerial photography, I’ll go into the mechanics of actually hanging a camera from a kite line, and convincing it to do what the photographer wants.  The approach used can be anything from quite simple to otherworldly complex.  A lot depends on what the photographer actually needs, but even more depends on what the photographer is convinced they want.  It’s important to keep these two ideas separate when you look at hanging a camera from a kite line.

Lightweight Rig - Ready to Fly

By far the simplest KAP rig I use is one I designed spedifically for doing mapping.  It was built for one specific trip, but it’s such a versatile rig I’ve used it numerous times since.  The requierments of the trip drove the design:  For starters, there is very little wind at the site, so lifting a heavy KAP rig was out of the question.  The bulk of the weight in this rig is the camera itself.  The rig’s weight is almost negligible.  For the purpose of mapping, all the pictures needed to be as orthogonal as possible, so there is no provision to tilt or pan the camera.  And we would need to take pictures over the course of several hours with no opportunities to change batteries during the flight, so battery life was of paramount importance.

There is no provision for the photographer to tell the camera when to take a picture.  Instead the camera is running CHDK, a toolkit that runs on top of the camera’s native firmware.  In this case CHDK was running an intervalometer script that let the camera take pictures every five seconds without any user intervention.  No mechanical linkages, no servos, no fancy electronics, just the camera itself running a pre-canned program.

Lightweight Rig Airborne

In the end the rig performed marvellously.  Complete with camera and the four AA batteries the camera requires, the rig came in just over 450g.  It flew on one set of batteries for two straight days, and took more than 2,000 photographs.  The photos from that trip are being used to map an archaeological site, and will be used in papers that should be published in the next year or so.

Current Rig - Late 2008

At the other extreme is my radio controlled KAP rig.  It’s built almost entirely out of off-the-shelf parts from Brooxes, the main supplier of commercial KAP equipment. The rig allows the photographer to pan and tilt the camera, and to operate the shutter.  Brooxes sells other components that would allow the camera to rotate from horizontal to vertical, and other accessories exist that allow the photographer additional control over the camera itself.

The rig started off as a Brooxes BBKK, but over the course of a few years I added a carbon fiber leg kit, gear reduction for the pan axis, a set of PeKaBe blocks for the suspension, and a number of other improvements.  Two changes have been made since this photograph was taken:  The first was to replace the aging 72MHz AM radio with a 2.4GHz Turborix.  The second was to remove the shutter servo and replace it with a GentLED-CHDK.  Unfortunately I haven’t photographed this rig since the changes were made.

The GentLED-CHDK is one of the cooler pieces of hardware I’ve bought for my rig.  It is a smart cable that plugs into the RC receiver on one end, and the camera’s USB port on the other.  When the photographer flips the shutter control on the RC transmitter (in my case I set it up as a switch rather than a joystick), the GentLED-CHDK sends +5V down the USB cable to the camera.  One of the features of CHDK is that you can monitor the +5V line on the USB port and take action when the camera sees it.  In my case I run a script on my camera that says as long as +5V is being applied, behave as if the shutter button is being held down.  In single-shot mode, this means each time I flip the switch the camera will take a picture.  In continuous shutter mode this means that I can hold down the switch on the transmitter and the camera will keep taking pictures as fast as it can, roughly every 1.1 second.

The two rigs are as different as they could be and still get the job done.  One was the product of a few hours of thinking and about an hour’s worth of time in the shop.  Total expenditure was maybe $50 for the Picavet suspension, most of that being the PeKaBe blocks.  The bulk of the rig came out of the scrap box.  The other was the product of a few years of tinkering with a commercial rig.  Total expenditure is probably several hundred dollars by now, but still probably less than a good carbon fiber tripod and professional ball head.

What is important to take away from this is that there is no one right way to hang a camera from a kite line.  And depending on what you actually need, an extremely simple rig like the ortho mapping rig may get the job done just as well as a more complicated, heavier rig like the BBKK.  Before becoming discouraged at the prospect of designing and building a rig from scratch, consider the commercial options.  And before becoming discouraged by the cost of the commercial kits, consider the possibility of simplifying your requirements and making one yourself.

It’s possible for anyone to do aerial photography.  If you want to do it, do it.

— Tom

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