Everyone knows what FaceTime is for: face to face communication. But what happens when you put an iPhone behind the eyepiece of an astronomical telescope and make a FaceTime call? Delightful, remote viewing of the moon and planets.
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I have a friend, Michael Weasner, who is an amateur astronomer near Tucson, Arizona. On Sep 23, he called with an idea. "Let's try a FaceTime session with my iPhone 5s at the eyepiece of my telescope." It worked beautifully. Here's how Saturn looked, live, here in Denver, via FaceTime from his observatory.
Saturn, cropped from iPad 3 in FaceTIme call.
How it Works
If you look into the eyepiece of an astronomical telescope focused on an extended object like a planet or the moon, your eye will see a magnified image. If you, instead, place a camera and its lens, focused for infinity, at the point where your eye would be, it can capture the image. This is called afocal astrophotography.
Mike got the idea that instead of capturing the image with his new iPhone 5s, he would instead use FaceTime and start a session with me. What I saw on my iPad 3 was, of course, exactly what his telescope was pointing at. (Shown above.)
This is not extraordinarily easy to do. It's best to have a special holder that places the iPhone exactly where it needs to be. It takes some practice. Here's what Mike's setup looks like.
Example afocal setup with iPhone, eyepiece and telescope
We also looked at Venus, which was just beyond 50 percent illuminated, via FaceTime. Here's what I saw on my iPad 3, in realtime.
Venus, slightly more than 50% illuminated, cropped from iPad 3 in FaceTIme call.
The reason why we were limited to the planets (also the moon) is because the realtime, low-level sensitivity of the iPhone's CCD is limited. For example, I couldn't see Saturn's brightest moon, Titan, on my end, while Mike could easily see it in the eyepiece.
Technical Notes
During our FaceTime session at 8 p.m. MDT, 23 September, both Venus and Saturn were low on the horizon, just below 10 degrees, so there was a lot of atmosphere to see through along with some low-elevation turbulence. (See the Sky Safari image below.) That detracted from the sharpness of the image in my FaceTime screen shots. Also, these two images above were cropped from the iPad's 2048 x 1536 resolution to include just the planet's image, suitable for Web publication.
We thought it would be helpful to compare those images to direct afocal photography.
About 30 minutes earlier, when the planets were higher, Mike took photos directly with the iPhone 5s iSight camera. The Saturn photo was made with a Meade 9 mm eyepiece, and the Venus photo was the best frame of a slo-mo video with the same eyepiece and a moon filter (to reduce the brightness.) During editing, Mike changed the orientation of Saturn and Venus, for publication at his website, so that's why they appear at a different angles below than the FaceTime session.
Direct afocal images, iPhone 5s, 30 min earlier. Orientation altered in editing.
I asked Mike how the 9 mm eyepiece at 222x translates into an image on the iPhone. He wrote: "Any camera sees what the eye sees when doing afocal imaging. So, depending on other factors (digital zoom, distance of screen from the eye, etc), the view seen approximates what the eye would see if actually at the eyepiece."
Equipment Details
Here's a photo of Mike's observatory, a Sky Shed POD, manufactured by a Canadian company, Sky Shed.
Cassiopeia Observatory. Photo taken with iPhone 5s and new flash capability.
Here are the details of the equipment used at the observatory.
- Meade Instruments 8-inch (20 cm.) LX200-ACF
- f/10 2000mm focal length
- Meade 9 mm eyepiece. Effective magnification 222x
- iPhone 5s, space gray, iOS 7.0, using rear/iSight camera and FaceTime.
- Homemade afocal adapter
- AT&T 4G cell network from observatory
Here are the details of the equipment in Denver.
- Apple iPad 3 (Retina,) iOS 7.0
- FaceTime app
- Home Wi-Fi via Comcast, Apple AirPort Extreme (802.11n)
Here is Mike Weasner's Cassiopeia Observatory report that has more details. For reference, here is what you'd have seen with the naked eye, looking roughly West (243 deg) using a terrific iOS app called Sky Safari.
Screen shot of Sky Safari for iOS, looking WSW, Sept 23 about 8 pm MDT
Observations
This technique could be pressed into service by any amateur astronomer with the right equipment to create a virtual star party for remote observers. The technique could also be used with a microscope, binoculars or even an iPhone with an attached telephoto lens. All this might be just the beginning of what could be done with the marriage of advanced optics, an iPhone, FaceTime and the Internet.