Afocal Cell Phone Adapter for Solar
Saturn taken with Android Eris cellphone and described
||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.
|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
Meade cylindrical eyepiece |
||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 ep 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 a barlow might help.
|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 with inserted eyepiece
Adapter with inserted eyepiece
Sample video taken with cell phone and adapter.
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.