Prototype iPhone afocal adapter
Based on my experiments with using the iPhone for afocal astrophotography, both the original model (for stills) and the iPhone 3GS (stills and video), I decided that some sort of fixed mounting for the phone would be preferable to handholding the phone's camera lens over the eyepiece. Handholding works but it is difficult to keep the object within the camera lens field-of-view. I searched the web for an existing iPhone afocal mounting but none apparently exists. I considered purchasing an iPhone photographic tripod attachment which would allow me to mount the phone on my old (and no longer used) Scopetronix "Digital Camera Adapter". I also thought about the Gorillamobile but didn't know if its legs were long enough to reach around the phone and encircle an eyepiece. So, I decided to look at what I had in my closet that could be used to hold the phone. I discovered some tips online that mentioned using the plastic packaging from the iPhone box as a holder for a photographic tripod attachment. And then I remembered that I had made an iPhone Easel (http://web.mac.com/jhearne/iWeb/Site/Easel.html), which works great when I use the iPhone as a timer for my D70 DSLR astrophotography. Could I do something similar that would hold the iPhone over the eyepiece? One thought was to just wrap the wire around the phone and the eyepiece, but I didn't think that would be secure enough. Since I already had the Digital Camera Adapter, could it be used to hold the phone with the wire? Ah ha, the beginnings of a concept. My initial prototype is shown above. What follows is how I made the prototype.
Here’s the camera adapter piece that I used:
I did some tests by holding the iPhone over the adapter. Hum, it looked like a possible solution. However, I didn't have any 10-gage rubber-coated wire available, so it was time to drive to a hardware store and get a short length. I purchased 48" (for less than $2), which was more than enough to prototype my concept and allow for future projects. I then cut two lengths of 9" and 12" to securely hold the iPhone in two directions on the camera adapter rod. It seemed like my concept should work. The next step was to assemble the prototype and test it at the telescope.
I opened the observatory at 1815 MST, on Wednesday, 1 September. Temperature was 102°F, under clear skies. At 1824 MST, viewed Venus. The view was good at 619X (9.7mm eyepiece + 3X TeleXtender), as the planet was still well up in the sky 20 minutes before sunset. I then took a video with the iPhone by handholding it over the eyepiece (afocal 619X). Here is one frame (unedited) from that video:
The phase of Venus clearly shows.
I then began assembling my iPhone afocal adapter prototype. I first tried out all my 1.25” eyepieces with the Digital Camera Adapter. These eyepieces fit: Meade Series 4000 26mm, Meade Series 4000 9.7mm, Meade Series 5000 5.5mm (barely), PST 12.5mm Kellner, OPT 15mm, and Scopetronix 40mm. The adapter would not work with the Meade 5000 26mm eyepiece, nor with my 2” eyepieces.
I then began playing with the wires to determine what positions and orientations would work best to securely hold the iPhone. The wire was wrapped around the rod and the locking rings were tightened. Next, the wire was bent to hold the iPhone in place over the eyepiece. Here’s how the prototype looked at this stage:
I attached the adapter to the 9.7mm eyepiece (plus 3X TeleXtender) and inserted the iPhone (seen in the photo at the top of the page). Once the iPhone camera lens was lined up over the eyepiece, I captured a video of Venus; here’s one unedited frame (overexposed):
Some things I noticed from this first test:
1.The prototype worked. There was no image blurring or movement from trying to handhold the phone camera lens over the eyepiece.
2.As obvious in the photo above, the camera lens needed to be much closer to the eyepiece to avoid serious vignetting.
3.The wires holding the phone need to be more tightly attached to the adapter rod and to the iPhone. The coated wires are slick and allow the phone to slide around too much, with a risk that the phone could slide out and drop to the floor.
4.Focusing the eyepiece with the eye (without the phone attached) is difficult with the wires sticking up.
I repositioned the phone to be closer to the eyepiece and took another video of Venus. Here’s an unedited frame from that video:
I will continue to work on the prototype, but during the daytime instead of inside the observatory at night under red light illumination.
At 1945 MST, I began doing some DSO observing with the 8” telescope. During the next 90 minutes I observed the following in various eyepieces: M13, M92, M51, M82, M22, M4, M8, M15, M27, M2, M20, M17, M5, M16, and the Double Cluster.
At 2120 MST, slewed to Jupiter, low in the east and still behind a tree. 2145 MST, it cleared the tree. I attached the iPhone afocal adapter prototype to the 9.7mm eyepiece (plus 3X TeleXtender) and captured a video. It was way overexposed. I attached a moon filter to the eyepiece and did another video. This is one frame, unedited, from that video:
Once I get the prototype design finalized, it looks it should be a good accessory to have for planetary and lunar astrophotography.
I then did some Jupiter viewing. It was still too low in the sky for good viewing at 619X, or even at 364X (5.5mm eyepiece). But the view at 206X (9.7mm) was good. And at 133X (15mm), several cloud bands were easily seen. The four Galilean Moons were also visible.
It had been a long day of errands and working on the prototype concept, and I was tired. Closed the observatory at 2225 MST, 75°F.
Thursday, September 2, 2010