How to Make a 3D Image Of Moon Features
After my first effort to take moon photographs with my NexStar 5SE
telescope using the Celestron
NexImage astro-camera, I proceeded with the tedium of processing a good
nights' images. I run a stacker program written in Yorick, which while crude
in many ways, has the particular features I desire. I was pretty pleased
with the results, as the following image of the Lunar Apennine mountains
Lunar Apennines with NexStar 5SE
In evaluating the
effort, I compared the images with similar ones taken some years ago with my
handy Meade ETX 90.
I was critically comparing the details to see how well the NexStar
performed, as I know from previous research that the ETX 90 does an
excellent job for its size. I found the NexStar 5SE did indeed do a fine
job, as is illustrated at the
NexStar 5SE Images web page.
As I worked through my image processing and comparisons, it occurred to me
that some of the images gathered by the two telescopes were of quite similar
areas, but yet looked a bit different in perspective. I realized that the
differences were likely due to the moon's libration.
Libration, if you're not familiar with the term, is the perceived
apparent wobbling of the moon over long periods of time. It occurs because
the moon is in a slightly elliptical orbit around earth, and thus at times
we can see a bit more of one side or the other due to this orbit. If the
moon were in a perfectly circular orbit, locked in phase as it is in its
orbit, we'd be able to see precisely 50% of its surface. But with libration,
we can actually see more like 60% over time.
I've read before, years ago, that one can make use of this to create
stereo pairs of photographs. The libration variation of the moon's
relationship to earth is kind of like looking at the moon with a super
wide 3d camera. All I had to do was crop, rotate, and adjust contrast
on images to match them up, and place the ETX 90 photos next to the
NexStar images to get stereo pairs.
So below are presented some selected pairs. If you've not looked at
stereo pairs before, it can be a bit tricky. It works best if you view from
around 14 inches or so from the terminal, and try to relax your eyes. Soon
you should see what appears to be a pair of images just a bit out of
alignment in a superposition. Concentrating on that image will usually cause
the apparent superpositioned images to snap into alignment. It helps
sometimes to close one eye at a time to help notice both images.
When the magic happens, the 3D effects will suddenly become apparent.
Mountains and other raised areas will show depth instead of just
If you can't get the effect, try holding a sheet of paper between
your eyes, letting it extend from your nose toward the screen. The
idea is to limit the vision of each eye to see only one image, and the
brain will thus combine them into the 3D image.
The images are designed to work when the separation between images is
about what your eye separation is. You might try increasing or decreasing
the size of the image to achieve that goal.
Don't try too hard or too long, as you'll likely get some eye discomfort.
old days, there were viewers made for this purpose. You've
probably seen them. They had a pair of eye cups on one end to hold up to
your eyes, and a bar that held the stereo images about a foot away from the
More recently was made a device called a
made to view pairs of images as a single stereo image.
Lunar Apennine Mountains in 3D
Ready? Let's start with the mountains shown in the previous image,
the Apennine Mountains:
Albategnius Crater Region in 3D
Were you able to see the 3D effect? Try the following of the
Albategnius region. What I seem to see here is that the floor of
Ptolemaeus seems to sit at a lower elevation than that of Albategnius.
Just from viewing single images I'd never noticed this. Also, the separating
region between Albategnius on the left and Ptolemaeus on the right
shows an almost pyramidal rise in 3D.
Tycho Crater in 3D
Tycho crater is next, lying on the a very rugged region of the moon. With
2D, there's clearly a lot of jumble, but in 3D, the jumble and Tycho's rim
take on more character. In the 3D image, it is more clear that Tycho's walls
rise considerably above the surrounding rough terrain.
Hyginus Rille Region in 3D
And last but not least is the Hyginus Rille area. This image suffers a
bit because the older ETX 90 images wasn't quite as sharp, but still the
raised area below the rille takes on more character in the 3D image. The
dark spot near the bottom of the right image isn't an actual lunar feature,
but was a piece of dirt on the CCD.
Had enough? Were you able to see the 3D effect? Hopefully you don't
now have a headache.
If you're ready for another go, notice that in the 3D images, more
subtle undulations in the terrain are visible, especially in the
Hyginus Rille image. In any event, I hope you had some fun, and maybe
got some ideas for your own astro-photos.