[Stonius (Markus)]

Just a note; for photographic purposes, the eye 7cm separation is not the standard separation between the optical axes for various reasons, mostly to do with the fact that sterescopic 3D is an illusion and not actually how we see the world in real life. There are fixed lens hobby 3D cameras with this separation, but they typically deliver terrible, unwatchable 3D. All professional cameras have a mirror rig that allows them to vary the interaxial distance. Most shots in the movies you see are between say, 5 and 50mm interaxial, often moving during the take as the scene changes.

However, for extracting data (photogrammetry), much greater interaxials are often used.

As far as your problem goes it's about angles. Typically a 3D image (for visual use) is limited by the degree of difference between the two views once the convergence point has been set (the moon). If that didn't make sense, look at your finger in front of your face. Your eyes turn in (converge) on it. Notice how the background is different between each view? The percentage of the screen that is different is the key in any stereoscopic image. The maximum is usually 3-5% of screen width before your eyes start to bleed. In your case, because the background will be black, you can probably get away with a bit more - all that will happen is the moon will become rounder (up to a point). But given that the same side of the moon always faces us (more or less) the question is will there be enough parallax to get 3D?

Scaling it down to terrestrial measurements, it's like having a 12.7mm interaxial on an object that is 35.7cm away from the camera. So yes, yu should be able to 'see around' the edge of the moon enough to get a stereo shot. The answer suprised me, but yes, it should be possible. Keep in mind that the thing you are hoping to capture, ie the 'roundness of the moon', will be somewhat flattened by the use of very long lenses.

You could try a baseline that involves taking an image just after sunset and just before dawn and allow the rotation of the earth to give you the required distance. (slight distance in phase shouldn't be an issue over that period of time.

Or possibly you may want to try using the natural lunar librations as a means of 'seeing around the edge' of the moon (as this is what creates the 3D effect. Hope that helps.

The best effect overall will be if you can set the moon against a field of stars (best photographed separately - the real stars won't cut it in this case) because its the parallax between moon in the mid ground and the background that really brings out the 3D. Maybe throw the ISS in the foreground for more depth! :-)

Cheers and good luck!

Markus

source; Me! (I used to work as a stereographer).