NavList:

Bill,

You wrote:

"I have seen various arrangements whereby a smart phone can be attached to a monocular as an enhanced zoom. So my thought is if I want to film the taking of a (eg sun) sight with my smart phone camera could I use the same type of mounting. One thing I don't understand is how a phone camera manages to make a focused image from an eye-piece.  I thought one needed to add or remove some optics. Does it only work on some telescopes and monoculars or is it because the phone camera is so small?"

I see no reason why you couldn't do that. Celestron has a some nice mounts for attaching your phone to any kind of scope. I used something similar with my telescope to take this video and this one. And for this video, I was simply holding my phone up to the eyepiece.

You don't need to add or remove any optics, because the phone's camera lens is positioned at the focal point of the eyepiece - where your eye would normally be. And I do think the fact that the sensor is near enough in size to a human pupil probably helps. You may have to adjust the exposure, brightness, etc. on your phone. Although you may also be able to use the sextant shades alone to get a good shot. As you mentioned, you can even use the camera's zoom as you would normally.

In the videos I linked above, you can see my phone adjusting the focus on the fly - trying to get the sharpest image. Most smartphones have the ability to lock the focus so you don't get that periodic blurring and/or changing image size. I just didn't think of enabling that when I was recording. IIRC, I wasn't using any of my eyepiece filters (e.g.: neutral density) for those shots. The phone simply compensated for the dynamic range on its own.

Anyway, I think this is a great idea. And I'm kind of embarrassed that I didn't think of it before you mentioned it. Not only could you record sights for instructional purposes, but if you timed the recording just right, you could analyze it later at your leisure to see exactly when 'contact' occurred. All you would need to do is set the sextant at any convenient angle and wait for the body to pass through it. And you get the added benefit of looking at a large screen during the sight, as opposed to squinting through a telescope. In a way, it's like turning your smartphone into a sextant. Brilliant, really.

Cheers,

Sean C.