Archive for October 30th, 2015

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Digiscoping with the GoSky universal cell phone adapter

October 30, 2015

Bird on a stick - 50x

As I mentioned in the moon video post, I recently got a GoSky universal cell phone/eyepiece adapter. So far I’ve tested it on some birds during the daytime, and on the moon after dark. Here’s a Northern mockingbird at 50x, about 125 feet away.

C80ED set up for digiscoping

I did most of the digiscoping with my C80ED and a 12mm Plossl (50x). I tried other eyepieces but for my purposes the 12mm Plossl delivered the best balance of magnification, true field, and image brightness.

C80ED digiscoping business end

If you haven’t seen one of these cell phone adapters, it has a diamond-shaped, padded clamp that screws down around the eyepiece, and another padded clamp to hold the phone. The bracket for the phone can slide up and down and rotate relative to the eyepiece clamp, so you can get the phone’s camera centered over the exit pupil of the eyepiece. As you can see here, the phone bracket is wide enough to hold an iPhone 5 with a heavy Otterbox case. I prefer to leave the case on while shooting – it’s rubber, so I can crank down the adapter bracket and make sure the phone is truly secure. Plus, it’s one less thing to do during setup and teardown.

iPhone earbuds remote shutter release

You may be wondering why I have earbuds hooked up to the phone. It’s because of a very nice feature with the iPhone 5 and 6 (don’t know about other iPhone models or other brands of smartphones) – the volume buttons work as shutter release buttons, which is often handier than trying to press the button on the screen, AND this functionality extends to plug-in volume buttons like those on the earbud cords. So you can plug in your came-with Apple earbuds and use the volume control there as a remote shutter release for hands-free, no-shake photography.

Fanned tail feathers - 50x

That mockingbird again, fluffing its tail feathers.

Waning gibbous moon 2015-10-28

Here’s one of the moon. The seeing was punk last night so I know the system was not performing anywhere near its limits. I’ve done far better holding the phone by hand on nights with better seeing, but only by dumb luck, taking loads of pictures, and throwing away all but the best. Using the adapter I get much more consistent results, even if the seeing makes them all consistently lousy on a given night.

The biggest problem with this setup so far is that the lens of the iPhone camera is bit fish-eyed and that introduces some kind spherical distortion (I believe it is positive or pincushion distortion – feel free to educate me in the comments) in the image. It’s not so bad in this cropped picture:

European Starling x4 - 50x

But check out the diverging power lines – which are parallel in real life – in the unmodified original:

European Starling x4 - raw shot

These are European starlings at 50x, again with the 12mm Plossl, from about 250 feet.

I did lots of back-and-forthing between camera and the various eyepieces to confirm that the distortion was in the camera and not in the telescope or eyepieces. It’s a fairly minor annoyance for me – I’m not expecting world-class results out of my smartphone camera. Just something to be aware of.

European Starling - 100x

I tried going up to 100x with the 6mm Expanse on this starling. It caused a lot of vignetting – even in this severely cropped photo, you can see that the corners are dark. I’ve had this problem with using too much magnification with handheld afocal photography as well. I think that as magnification goes up and the exit pupil goes down, it’s progressively harder to fully illuminate the camera’s CCD.

This may seem like a lot of caveats and complaints – distortion, vignetting, etc. – but they’re all problems that come along with doing afocal photography with a phone. The adapter itself is dandy. It holds the phone and eyepiece securely and without stressing either one or leaving a mark, it’s easy to put on or remove, and it adjusts easily. I wish now I’d gotten one a lot sooner. There are lots of interchangeable brands on these things – if you want the GoSky verison, it’s here.