afocal – A Darker View

A Universal Afocal Adapter

A couple weeks ago at the volcano I let quite a few folks take imagery of the lava using the afocal technique, simply holding the phone up to the eyepiece. This works rather well as the phone uses a lens much like the human eye, about the same aperture.

Shooting afocal with an iPhone and the TV-76mm 'scope — Shooting afocal with an iPhone and the TV-76mm ‘scope

The only real issue is holding a phone in just the right spot. Folks wanted video, but holding the phone steady is a real challenge. I had thought of making something to do this many times, last weekend I did it.

A session of playing around in 3D CAD resulting in a couple bits of clever plastic printed with the 3D printer… Done.

There are commercial solutions for this available, quite a few actually. But most of these are intended to adapt to a single phone, using some sort of clamping arrangement that you have to setup for a particular phone. I envisioned something that was more universal, quickly adapting to any phone.

The method I chose was a sliding magnetic platform that holds the phone. Just a simple shelf actually, set the phone on it and slide until you get it lined up. The base piece is printed with a recess into which a steel plate is set. The slider has three 8mm x 2mm neodymium magnets to securely grab the steel plate.

It took a bit of work to cut and file the steel plate to neatly fit the base, a bit of inlay work. Otherwise making the piece is quite easy. The only design issue is that this adapter is setup to fit a single eyepiece, a Televue Panoptic 27mm, and cannot be easily adapted to others.

The 3D CAD files are linked below. I have included the SCAD source file to allow tinkering with the design, possibly adapting to a different eyepiece. Both parts should be printed with support on, the pockets for the glued bits will have to be cleaned out, the resulting rough surfaces just right to recieve epoxy.

Afocal adapter 3D CAD files

At the Keanakakoʻi Overlook I was able to test the adapter with a variety of different phones, both iPhone and Android, graciously lent to me for my experimentation. OK, the owners may have wanted a few lava photos. There was no difficulty using the adapter other than a moment or two needed to line up the camera with the exit pupil of the eyepiece. The result was more than a few smiles.

Luna

Afocal Luna

With a few public outreach events this last week I had a few opportunities to hold my phone up to the eyepiece and shoot a few shots of a waxing Moon. The iPhone 5S does have a notably better camera than my old 3S. The afocal method does provide some nice snapshots of the Moon.

As usual I demonstrated the technique to our viewers, showing them how to use their phone to shoot the Moon. The result? Big smiles and happy folks, thrilled to have some great Moon photos of their own.

Luna

iPhone 5S photo of the Moon through a NexStar 11", afocal method with a 35mm eyepiece — iPhone 5S photo of the Moon through a NexStar 11″, afocal method with a 35mm eyepiece

First Quarter

Quarter Moon — A 53% illuminated waxing Moon, afocal w/Canon G11, TV-102 & 32mm Plössl

iPhone Moon

Despite numerous attempts, I had never managed a decent shot of the Moon using an iPhone. When showing people how to do afocal photography, I have leaned how to make just about any compact camera perform nicely, but routinely seen nothing but trouble with cell phone cameras.

Lunar photography is incredibly popular with folks using the telescope, a great activity for a night with a bright moon. Long ago I found that an inexpensive 20-25mm Plössl is a good match for the lens of most compact cameras. On a 1-2m focal length telescope this combination can produce very nice lunar photos. The setup does not work with cell phone cameras. Though people do try, the results have been routinely disappointing.

Working a resort star party recently, I discovered a combination of telescope and eyepieces that works very well. A C11 telescope, an f/6.3 focal reducer, and a 20mm Nagler type 2 eyepiece produced very nice photographs with several different cell phone cameras. The result was a very happy audience and a lot of great lunar photos. As people walked away from the telescope they were rapidly replaced by a crowd holding glowing screens, all wanting to get a nice lunar shot for themselves. I will have to explore other telescope/eyepiece combinations to find another solution that does not involve a $500 eyepiece.

iPhone Moon — An eleven day old Moon, taken with an iPhone 3GS, a C11 and a 20mm Nagler 2 eyepiece

Afocal Photography

When doing any sort of public astronomy, showing folks the beautiful sights available to a telescope, I often hear the question “Can I take a photo of that?” The person asking the question is usually holding the ubiquitous compact digital camera. They are often surprised when my answer is “Yes”.

It is indeed possible to manage hand held shots of bright astronomical objects by simply holding the camera up to the eyepiece. There are a few tricks to making it work, but nothing that can not be demonstrated in a minute or two. The resulting photographs can be quite pleasing, definitely worth showing to friends and family along with the rest of the Hawai’i vacation shots.

The method of positioning a camera with a lens in front of an eyepiece is called afocal photography, or sometimes digiscoping. Afocal has been around for a while, but was not considered a practical photographic method by most. The advent of common digital cameras without removable lenses has changed this.

Enjoying the Moonlight

Deb and I did a volunteer evening at the VIS last night. A great night with a great crowd, the sort of evening that defines the reason we continue to volunteer at the Mauna Kea VIS. Lots of great questions, great conversations and a little learning about the sky and Mauna Kea. As the southern cross hung above the slopes of Mauna Loa my green laser was busy pointing out constellations and bright stars.

The only real problem with the evening was the nearly full Moon hanging in the sky. The bright moonlight drowning out many of the deep sky objects we would normally view. Even bright objects like M13 were merely dim smudged in the eyepiece in place of the beautiful sights they offer under darker skies. With these conditions much of the telescope viewing was concentrated on the Moon and a beautiful planet Saturn.

One activity that is always a hit with a bright Moon partly makes up for the loss of dark sky viewing. I hold and quick course in introductory lunar photography using the afocal method. Show a few people how to take lunar photos and there is soon a line of people waiting at the refractor for their turn to try a few frames. A few hints and people are quickly taking great lunar shots, a photo and a memory to take home from the mountain.

The evening sped by quickly, spent in conversation with guests from the islands and from across the US. People ask about the sky as seen from different latitudes and locations. A few visitors from other countries add their perspective. It is often interesting to hear about other names for constellations or to learn bits of folklore from many other cultures.

So often the crowd disappears an hour after dark, driven off by the cold and wind. This night many didn’t go until it was time to shut down the telescopes. I guess they were not ready to end an enjoyable evening under moonlight.