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Afocal Cell Phone Adapter for Solar System Objects
Afocal Cell Phone Adapter for Solar System Objects
At a public viewing session out at Broemmelsiek Park in late March or early April 2011 something interesting happened. We frequently get local college students taking an Astronomy class and that night was no exception. Three students and their teacher from St. Louis Community College in Wildwood were present. By 10 p.m. things had thinned out a bit and the four were pretty much the only visitors left. Unlike some of the students who come because they were required to attend, these were really interested. They were looking at what I guess was Saturn through the 16" Jones-Bird and one of the guys asked if he could take a picture of it with his cell phone. Grant Martin, who was running the 16", said sure and the guy started snapping pictures with his Iphone. It wasn't exactly the easiest thing to do. It was hard to hold square with consistent spacing to the optical axis, hard to focus, and tripping the shutter did cause blurs. Still he persisted, the pictures were pretty good and the student was really excited about the results. So excited in fact that he posted them to his Facebook page and emailed copies to his friends. I regret to say that I don't have any of his images.
Saturn taken with Android Eris cellphone and described adapter
As I watched him making the exposures I wondered if there would be any way to make the process any easier. I though that if everything worked out it would make a wonderful tool for public viewing sessions. Imagine the interest level at a public session if someone would say "If you have a cell phone with a camera you can take a picture of that now." Within two days I'd thrown together an adapter out of scrap wood and glue that easily mounted to the club's C14 or any other 1 1/4" scope, allowed framing/centering and zooming, held the cell phone steady, and if nothing else gave a nice view of Saturn on the cell phone's display. I tried to take about 20 pictures on the C14 but I was a bit disappointed with the actual results. It seems that anytime I pressed the exposure button, the whole system would shake and I'd get blur. Jim Roe was impressed enough to ask me to make me one and I gave him the original and cranked out another the next day. It is very possible to make an adapter that "fits" a specific cell phone. I opted for a generic adapter so that I could mount a wide variety of phones so others could take pictures with it.
Cell phone mounted on adapter with rubber bands
I played with the adapter for a few nights but couldn't figure an easy way to remove the shake without making some cable release thing so I put the project on the back burner for a while. About a month later ( June) Jim mentioned the idea at a DigitalSIG meeting and I thought about the problem again on the way home. About the Daniel Boone Bridge I wondered if my cell phone had an App with provisions for a delayed release. Twenty minutes later and I'd downloaded two different possibilities. An hour later I'd even found a delayed timer on my phone's native app.
The key to the adapter is an old (1980s) Meade 20mm Erfle eyepiece that lacks a rubber eye ring. The only thing special about the eyepiece is that it's outside is pretty much 1 1/4" cylindrical. That allowed me to do drill a 1.25" hole through a block of wood (3"x5"x2") and slide the block over the eyepiece with a tight fit. Most cell phones have a lens that is closer to the top so the hole should be located appropriately. I suspect that most eyepieces could be adapted, but a cylindrical eyepiece is much easier to use. The cell phone is rubber banded to the block with the camera lens centered over the hole. The focal length of the C14 is pretty long. On other telescopes I do use a barlow.
Meade cylindrical eyepiece
In practice, first find the object with the telescope and 20mm eyepiece and try to get the best focus possible. Once the object is centered and focused, rubber band the cell phone to the block. At this point it is a good idea to shine a red light down the optical tube to center the camera over the eyepiece. Move the cell phone back/forth, up/down until the red light is maximized. If the cell phone has a zoom feature use it to get the best possible image, refocusing or recentering as necessary. You will probably need to experiment with the brightness/darkness to get the best detail otherwise the autoexposure will massively overexpose the object. Lastly, set the shutter delay to at least 5 seconds. If your cell phone has a burst mode you may wish to take multiple pictures with one press. Once you get used to doing it the entire process can be done in 2-3 minutes.
Adapter and eyepiece showing 1 1/4" hole
Sample video taken with cell phone and adapter.
Adapter with inserted eyepiece
rear view
Adapter with inserted eyepiece
front view
The hole on this end is 1 1/8"
While it would be nice to believe that deep sky objects could be captured with this combination, the cell phone's camera isn't sensitive enough to the low levels of light.
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