The View Up Here

Random scribblings about kites, photography, machining, and anything else

Back to the Panoramic KAP Rig

Posted by Tom Benedict on 14/11/2012

I got my pano rig out again over the weekend, flying it at the south end of Hapuna Beach. I flew my Canon T2i and 18-55mm lens set at 18mm. It was… less than satisfying. But I think it’s pointing me in a direction I was already heading, so in a way it was a good experience.

Two problems jumped out. First, using the 18-55mm lens at the wide end makes for fuzzy pictures with horrid chromatic aberration. In the past I’ve flown it set to 24mm. It performs far better at this focal length. I just wish I could use its full wide angle capabilities. Pity. But right now I can’t afford a higher quality wide angle lens – prime or zoom.

The second had to do with the pano rig itself. With the exception of one orbit of the rig, in every other orbit it had gaps in the sequence when the rig was pointing toward the beach. It’s as if the servo sped up, slowed down, and then sped up again at some other point of the rotation. I couldn’t stitch the images because there wasn’t enough overlap between images. In the worst cases there wasn’t ANY overlap.

This is simply unacceptable. What I wanted when I built this was a KAP rig I could put in the air and without fail come back with good solid sets of images I could stitch every single time. I’m not getting that. So obviously something has to change.

My original plan when I built this was to stick a relative shaft encoder on the pan axis. That way I could drive the rig to a real position, trigger the shutter, then rotate to the next real position. I punted on this when I saw how consistent my pan servo was. I probably shouldn’t have. It was good, but obviously it wasn’t good enough.

My plan now is to add a plate on top of the pan axis gear. The plate will have a series of small rare-earth magnets embedded in it. I’ll then hot glue a hall-effect sensor to the gear guide so it’s positioned directly over the ring of magnets in the plate. The Micro Maestro I’m using as a rig controller can be configured to use one of its I/O pins as an analog to digital converter. I’ll wire the hall-effect sensor to the ADC input and use that to sense the position of the magnet plate. That, in turn, will give me an encoder on the pan axis that I can use to position the rig for each exposure. The plate and hall-effect sensor should also stay inside the existing envelope of the rig. No extra things protruding out, and only one extra wire. It should have a minimal impact on the rig itself.

I hope this works. I’ve got a lot of work still to do on rig stability. But the rest of the rig has to work first. Then it’s time for post-sunset panoramic KAP!

– Tom

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9 Responses to “Back to the Panoramic KAP Rig”

  1. Tom,
    Glad to see you flying again…just a thought on your pano fail, are you sure the shutter actuation worked on the missing frames? I have had instances when the GentLed IR trigger seems to fail. I lke your idea of a DIT stepper motor for the pan….could it work out lighter than the servo?

    B

    • Tom Benedict said

      That’s an interesting idea! I’ve got some small stepper drivers from Sparkfun. I got a pair of motors for making an eggbot, but never built the thing. The motors are a little too hefty for a KAP rig. But a smaller stepper, say out of an old 3.5″ floppy drive, would fit the bill just fine. Hmmm!

      I haven’t checked to see if the shutter failed to trigger. This was via a GentFOCUS cable plugged directly into the shutter port on my T2i. I haven’t done any recent ground testing to make sure it’s tripping the shutter 100% of the time. That would be a good test to run before taking to the air again.

      I’m going to try to make some time this weekend to make the encoder wheel and test it out on the rig. It might mean no real flying time this weekend, but it’ll be time well spent in the long run. Next time I post about this I should have some pictures to share.

  2. That’s ‘DIY’ not ‘DIT’ btw!

  3. Have you looked at any of the manual Samyang prime lenses? Cheap and great image quality from what I hear. The 8mm fish eye or the 14mm prime would be ideal I would think for KAP.

    • Tom Benedict said

      OOOOH! Nope, I hadn’t looked at them before. Thanks for the pointer!

      I’ve got a question. Doing a search on Amazon for “samyang lens canon” shows up a bunch of Samyang lenses along with a number of Rokinon lenses. Two names, same maker? Or are these wildly different beasts?

      I’m not sure I want to go as wide as 8mm, but a 14mm prime would be right up my alley.

      Thanks again for the pointer, Ian!

      • The Samyang lenses are re-branded to several other names including Rokinon.
        14mm would be my choice from what little I understand of KAP. One of these days I would love to get into this style of photography… you can get some stunning images. Good luck and keep me posted on how you go.

  4. Ralf Hesse said

    What about making the camera rotate slowly and use an electronic compass to tell the system when to shoot? E.g., take an Arduino and a magnetometer sensor, rotate the camera with a stepper motor and shoot in 30° steps from north. That would also take care of random rotation of the rig which you could not correct for with the rotary encoder.

    • Tom Benedict said

      I considered using a magnetometer, and may still go there. But for now I’m still planning to go with the encoder. The reason is I’ve already got all the bits for the encoder. The magnetometer would require buying stuff, unfortunately. Time I have. Money for new parts is harder to come by these days. (And now Ian has me drooling over a $400 14mm lens!)

      But you raise another point as well: rotating slowly and taking pictures at pre-defined angles via the magnetometer. This is similar to the idea of burst KAP, which uses continuous rotation and an intervalometer on the camera. The only thing is with the original burst KAP approach you’re still at the mercy of random motion of the rig, variability in the intervalometer, etc. With your magnetometer idea, you’re guaranteed to get all the shots you need to fill the circle.

      But both ideas rely on continuous rotation of the rig. With this rig I chose not to go the burst KAP route of having a continuously rotating rig. Even though I’m doing most of my testing in broad daylight, the eventual goal of this rig is to do post-sunset KAP. I want to be able to use a shutter speed in the 1/100 to 1/15 second range, and still get sharp photos.

      Burst KAP relies on fast shutter speeds to work. That’s why this rig is set up to make small pan moves in between shots, with ramped acceleration and deceleration for each move. It’s more complicated than a burst KAP rig, but it does allow for longer exposures since the rig is sitting still when the shutter is tripped. It’s still at the mercy of wind induced rig motion, but that’s another question entirely. (It’s also why I’m so interested in stabilized KAP rigs!)

  5. rohan said

    Thanks for sharing this post with us,nice post.

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