Public Lab Research note

chosing a mobius camera to offer through kits store

by tonyc | | 2,131 views | 5 comments |

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What I want to do

I want to offer the right camera/lens combination through the kits store to support small form-factor aerial photography.

My attempt and results

I purchased some unmodified Mobius cameras for inclusion in a soon-to-be-releases stuffable kite kit. I asked them to also include samples of 6mm and 8mm lenses, as well as one camera pre-rigged with each, based on research and notes by pcoyle

They arrived today.



You can see the IR filter tacked to the back of these: IMG_1030.JPG

Here is the view from my desk, through insulating plastic, BTW, taken with the Mobius with factory wide-angle lens. factory.JPG

Here is the same view, taken with 6mm lens:


Here is same view taken with 8mm lens: 8mm.JPG

Notice blue color shift on both images with modified lenses.

Questions and next steps

Which of these is ideal for mapping applications?

Would it make sense to offer the camera with stock lens, and then lenses for self-install, or would it be best to just have the right lens ship installed?

Next step would be to fly test flight with all three of these options clicking away, then post results, make decision based on that.

Then I would order stock to offer in the store.

For now, I can put these in store as options, and note it is experimental

Why I'm interested

Want to make it easy for novice to get the "best" option based on our research, and have success on their first flights


A good focal length for mapping is probably around 35 to 40mm (35 mm equiv.). That is what the old A495 had (37.6 mm). More typical small PowerShots have a focal length of 28.5 mm, and they have been used a lot for mapping, although that is getting a little wide so it is hard to stitch things at the edges. Some PowerShots go even wider to 23.8 mm (S95, S100, S110), and they should be zoomed in for mapping. I think the standard Mobius lens is about 23 mm equiv. (3.7 mm actual), but I'm not sure about that.

I think a 6 mm lens on a Mobius has an equivalent focal length of 38.4 mm (assuming the sensor is 1/2.7 in). So that is probably good for mapping. The 8 mm lens would have a 35 mm equiv. focal length of 51.2 mm. That would make very nice maps, but getting complete coverage would be hit or miss.

So a 5 mm or 6 mm lens should be good for mapping on the Mobius.

For other types of aerial photography, like stitching oblique panoramas or just capturing landscapes in single photos, a 4.5 mm lens could be good. That provides a 28.8 mm focal length (35 mm equivalent) like a typical small PowerShot.

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Thanks Tony. Chris's comments seem on the mark, as one can see in the images from the various lenses in note,

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I'm thinking having the camera with stock lens, and camera with 6mm lens. Then offering the range of lenses as individual items for people who feel like running a conversion themselves.

Might be worth a color correction script, a la the one we install on the infragrams before shipping.

anyone remember who wrote that config file? thanks for all the feedback! t

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A custom white balance setting is easy to do using the msetup program. Just try different numbers for R, G, and B until you get what you like. First you should try the white balance presets (sunny, cloudy, etc) to see if they work well enough. They probably do for average situations.

The blue tinge in your photos could be an artifact of those particular photos. Was the camera set for auto white balance or a preset? For mapping (or any stitching), using a standard preset or custom white balance is best so auto white balance does not make each photo different.

Pat made a kite flight with an 8 mm lens and got good continuous coverage. All else being equal, this would be a very high resolution map. However, the longer the focal length, the more the photo is prone to motion blur. So using an 8 mm (50 mm equiv) lens for kite photos is an advanced exercise but can produce high resolution results.

The other characteristic of the lenses you might examine is distortion. Take photos of a grid and see how much the photo is warped. This is easy to do with a checkerboard, but more useful if the grid is >100 feet away. That allows you to also examine how soft the focus is at the image edges when the subject is at "infinity." This is a better analog of mapping photos. The trick is to find a distant grid-like subject that can fill the frame edge to edge. To examine focus, a high shutter speed (or tripod) is required.

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Couple things. I realized the mobius with the new lenses can be focused manually, just by screwing the lens further in or out. This was hit and miss, until I discovered you can view through the lens on these by running as a webcam. On my linux machine, this just meant removing the SD card, plugging it into machine via USB, then powering it on. I viewed in "Cheese" software, and dialled the focus in.

Also discovered you can get incredibly close with this, by focussing manually. Right down to one inch from object. This makes very shallow depth of filed images, but that's great for product shots. This could also be useful in doing detailed tutorials with small parts.

I messed around with color balance on the new lenses, and found that auto tends to override the blue nature of these iagme,s but also by manually tweaking the RGB in the syscfg.txt file I could get a decent, consistent color to the images.

once I settle on a method, I can document in detail. But basically I took image of white paper, then went into to Gimp and used color picker tool (the eye dropper) to select the white paper, and then looked at the RGB values of this color. I then altered the RGB numbers in config file to compensate for the % difference of these values. For example, the Red channel was (say) 180. This is a value out of 0-255 scale. This is 41% change from 180-255. I went to the config file. There the number is measured from scale of 100-999. I just napkin-mathed this out, starting with the RGB values for "cloudy" setting, and increased RGB by the % Gimp told me.

I am 100% sure this will make NO SENSE to ANYONE but I will use these notes to try to recreate and post another note on the topic, once I'm sure it acutally is repeatable.

At this point, I am happy with the 6 and 8mm lenses as potential mapping options. I have successfully converted an infragram camear to a mapping camera by swapping out the kit lens with one of the new 6mm ones. And it's not so very hard to do.

I'd be fine offering the stock camera + 6 and 8mm lenses through the store, as well as each as standalone items. On the fence about just having them ship to us with 6mm installed, adn whether to have all of these options, or just pick best configuration and sell that one only. I'm leaning toward the stock + lenses and instructions mode, as it's cheapest and not too difficult to pull off.

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