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Barney MagrathApril 19, 2019

Adapting an iPhone for Astrophotography

Global smartphone sales topped 1.5 billion last year. Many of those phones came equipped with impressive cameras, yet as far as I know, a smartphone image has never shown up on NASA’s Astronomy Picture of the Day website.

That doesn’t mean you can’t use your phone for astrophotography! The sky is the limit, providing you’re willing to invest a little time for what is a surprisingly low-budget, hands-on project.

I bought my first smartphone in 2015, which makes me a very slow adopter. The iPhone 6+ had been introduced the previous year and it had all the bells and whistles a photographer could want, including a 5.5-inch screen and an 8-megapixel color image sensor to print 8” x 10” photos at 300 dpi.

The first photo I took was of the full Moon through a pair of binoculars. I guessed that the iPhone camera lens would approximate my eye and, if placed correctly behind the eyepiece, would refocus the magnified image onto the focal plane of the camera. This idea is called afocal imaging or eyepiece projection. The alignment and interface hardware needed a little work but I had the background from my career as an optics technician at the Canada France Hawaii Telescope and Subaru telescopes at Mauna Kea, to work out a robust optical interface design.

Unlike Steve Jobs, who reportedly invested $150 million to develop the iPhone, I had, well, considerably less. But that’s okay, because I made a device that virtually anyone can make in a garage or workshop. Here are three different ways to photograph the night sky using an iPhone and some software and hardware hacks. And don’t forget to enable airplane mode so an incoming message doesn’t vibrate your phone!

First configuration: iPhone on a stationary tripod

In essence all you need to take a picture like this is manual control of the focus, a 15-second time exposure, and a RAW file output. Can the native iPhone camera do any of these? No! I downloaded an app called ProCam to do this. It currently costs $5.99.

ProCam gives you manual control over your phone’s settings. It will let you shoot in TIF files, which is important because the bit depth is much greater, giving you more editing headroom. (Also, TIF files are an order of magnitude larger than JPGs.)

I use a standard camera tripod and attach the phone using a cheap adapter that you can buy for about $10. Positioning the touch screen at head height, pointing horizontally, simplifies the learning curve. I shot a star field that includes Orion and Canis Major, since they rise above the eastern horizon in January. Imaging objects directly overhead is considerably more difficult.

iPhone on a stationary tripod

Barney Magrath

iPhone on a stationary tripod
On the bottom edge are lights from a faraway house. Above that are some bright stars of the winter circle: Procyon, Sirius and Rigel. The goal here is to make an image that looks exactly like what you can see with the naked eye.

Technical Details: Camera control app ProCam, no auxiliary optics, 15-second exposure in TIF, no zoom, processed Photoshop CS2, aspect ratio 3:2 (7.1 megapixels), no image stabilization, plate scale 61 arcseconds per pixel. Location: Santa FE, NM

Second configuration: iPhone behind a pair of binoculars

The key element in this setup is the optical bench, a piece of ¾-inch plywood. As you can see in the following picture, the binoculars are mounted so that the optical axis is parallel to the optical bench. The iPhone is then put into position as you would position your eye. As you look at your camera screen, you move the iPhone into the sweet spot’ behind the eyepiece. There is no mechanical connection between the camera and the binoculars.

iPhone behind a pair of binoculars

Barney Magrath

iPhone behind a pair of binoculars
This optical bench can be mounted on a stationary tripod or on a tracking mount. Notice the red-dot reflex finder to help you aim the binoculars as you would with a telescope.
Compact digital camera behind a pair of binoculars

Barney Magrath

Compact digital camera behind a pair of binoculars
Another shot of the optical bench, using a compact digital camera instead of a smartphone.

The bench is an “x-y-z table” that lets you move the iPhone in 3 directions:

x motion (left and right): The x-plate is a custom-machined aluminum plate with a long slotted hole. Loosen the black cap screw, slide the plate, and lock it down.

y motion (up and down): Edmund Scientific sells a low-priced lab jack, around $180. I modify it slightly by tapping some M4 holes in the top plate. The jack provides an up and down motion with a large rubber-coated knurled knob.

z motion (back and forth): The z motion is along the optical axis. It positions the camera to fill up an unvignetted field of view. This custom-made aluminum plate also uses long slotted holes, and black cap screws, to lock it down.

The key to the x motion and z motion working smoothly together is a couple of channels that are precisely milled in the aluminum plates.

Don't forget the other camera modes on the iPhone, especially the time-lapse mode, because moonrises and sunsets make spectacular subjects

Moon through iPhone behind a pair of binoculars

Barney Magrath

Moon through iPhone behind a pair of binoculars
This scene is low-resolution by design. To get maximum magnification I aligned, and focused, the iPhone camera lens to one side of the 8X binocular and then used the digital zoom in the camera (total magnification is about 48X).

Third configuration: iPhone behind a telescope

For this configuration, I placed the iPhone behind the eyepiece of a 70mm Celestron refractor picked up at the local thrift store for peanuts. Notice that the camera mount is an exact copy of the mount used with binoculars.

iPhone behind a telescope

Barney Magrath

iPhone behind a telescope
The optical bench is mounted on a battery-powered, equatorial tracking mount. Again you see the red-dot finder which is co-aligned with the center of the camera field of view. The ProCam interface is displayed on the iPhone screen.
Lunar eclipse via iPhone behind a telescope

Barney Magrath

Lunar eclipse via iPhone behind a telescope
The sky conditions for this total lunar eclipse on 21 January 2019 were terrible, with clouds and high humidity preventing precise focusing. However, it was good practice for low-light imaging and optical alignment using a short focal length eyepiece.

Technical Details: Camera control app ProCam, telescope optics 70mm f/10 refractor with 10.5 mm orthoscopic eyepiece and no filter. Location: Santa FE, NM

Read more: amateur image processing, amateur astrophotos

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