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MOON MOSAIC PROJECT |
Abstract: The goal of this project is to
create a large, high resolution, digital image of the moon. By
connecting a high resolution digital camera to both a television monitor
and an LX200 12" telescope, and piecing together many overlapping
images using photoshop, a poster size, photo-quality image can be
created. The final image can then be professionally printed
onto poster board.
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| Digital Cameras and Astrophotography: Modern
digital cameras provide a new and easy way to generate very high quality
digital images of bright objects in the sky - particularly the Moon and
the planets. The first task is to mount a digital camera onto a
telescope, the second to achieve a good focus, and the third is to find
the right settings for the particular photographic task.
The camera we will be using is an Olympus 2000-series. To
connect it to a telescope requires several accessories. Because
digital cameras do not have removable barrels, all photography must be
done via afocal projection. This means that an eyepiece is used,
and the digital camera is placed in close proximity to the eyepiece,
behaving as your eye would. It is one thing to hold a digital
camera near an eyepiece and observe that this technique works, but it is
quite another to take successful pictures.
The first step is to buy an extender tube that can house an
eyepiece. I found a good one at Scopetronix.
You probably will need to use a 20-26mm eyepiece. Larger eyepieces
will not fit in the extender barrel, and smaller ones will lead to
vignetting problems - only a small circle of light entering the camera -
which means resulting pictures need to be heavily cropped. You
also will need to get a threaded adapter to mount the extender tube to
the camera. Using an Olympus 2000Z, I was able to connect the tube
using two adapters - one a converter from the camera barrel to T-mount,
and the second from T-mount to the extender tube.
Extender tube (left) and adapter rings (right)
Once you have the equipment, the eyepiece needs to be
inserted into the extender tube, and then locked into place. It is
very important the eyepiece is both centered and aligned parallel to
the tube.
Extender and eyepiece (left), fitted eyepiece (right)
Once the eyepiece is contained securely in the barrel,
connect the barrel to the camera using the adapter. The other end of the
barrel has a 1 1/4" cylinder, which fits perfectly into an eyepiece
holder on a telescope. We are now ready to focus the camera at the
moon.
Olympus 2000Z with extender attached
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| Focusing: At first, using the digital camera
was a great relief from trying to focus a CCD camera, where there was no
way to assess focus without taking pictures. But even the digital
camera can be challenging to focus. This is because the auto-focus
does not work for viewing through a telescope, or at least is very
inconsistent, and hence the focus must be determined by viewing the
LCD. This screen is very tiny, and what appears to be in focus when
small may be quite blurry when viewed on a large screen (or printed on
paper). Even the digital zoom capabilities of the camera were not
very helpful. The first observations/photographs made using this
setup yielded quite a few blurry pictures that seemed focused on the LCD.
Fortunately, this problem can be solved. Most digital cameras
have a "video out" which sends a streaming video to a 1/4"
cable (which converts to RCA). This signal can be sent directly to a
TV (if it has an RCA input, or an RCA/Coax converter box), or directly to
any RCA input on a VCR. Now, instead of a tiny view-screen, the
camera view can be seen on the TV. With this larger view, it is very
easy to assess good focus. It also allows for quick views of
pictures already taken to assess detailed focus using the digital zoom.
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Video output Cable
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Moon image on TV
(from camera)
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Moon image
(without digital zoom)
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Same image
(zoom reveals poor focus)
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Note: This also allows for the exciting possibility of recorded
observations. Simply connect a VCR to the TV and record the video
output from the camera. You can make magnificent video tours of the
moon's surface.
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| Taking Pictures: Once the camera is securely
mounted on the telescope, and good focus is achieved, you are ready to
take pictures. The first steps are to: disable the flash, manually
focus the camera to infinity, put the camera in shutter mode
("s"), and set the camera to "timer" mode (where it
delays a few seconds and then takes the picture). You can also
operate the camera by remote control. Now, the two variables are
shutter speed and magnification.
The best way to take good pictures is to take a lot of different ones. At first, try taking pictures without zooming in.
Work your way through all the shutter speeds until you find the one that
generates the nicest image. Carefully analyze each image on the TV screen
using the digital zoom. Then try zooming in, or inserting a Barlow
lens in the telescope, and repeating the process. Remember the best
settings for later observations. They at least will be a good starting
point if conditions are a little different.
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| Creating a Mosaic on PhotoShop: To make a moon
mosaic, you need to take enough pictures of the moon so that every part of
its surface is contained in at least one photograph. The safe way is
to start numbering from the bottom left, and to take photos that overlap
quite a bit as you work your way up the moon. (Clearly #3 is not necessary
:-)
Moon grid: Be sure that all
photos overlap.
VERY IMPORTANT!!! - Be sure that all photos are taken
with the same magnification and exposure settings!!
Once the images are taken, the rest of the task can be done
in the computer room. The first step is to process and crop each
picture. Below is an example of this:
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Raw Image
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Cropped Image
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Processed Image
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The first image shows the problem of vignetting that often
arises when images are taken using the zoom (the cone of light from the
telescope cannot accommodate high magnification without introducing the
effect). However, there is a good region that can be cropped out and
enhanced. It is vital that the cropped images overlap!!!!!
Once all the pictures are cropped and processed, they should be placed on a
blank Photoshop background. The background should probably be several
feet in length and width - it can always be cropped later. The photos
should be placed according to number, roughly laid out in the shape of the
moon. Now it is time to put the puzzle together.
Start with the first two pieces. Place the first
roughly where it should be in the larger background. Now zoom in and
drag the second piece over the first until they match up. (Note: you
can change the layering at anytime in Photoshop.) You can choose an
individual piece and further enhance it to make the brightness match up at
the edge.
Above are two overlapping pictures of the moon. The
first step is to layer them so that the image surfaces match up. Below
is the result of this initial layering.
Initial overlap
There are two problems with this picture. First, the
brightness doesn't match. Second, the overlap is not perfect. By
adjusting the brightness so the photos match, it becomes much easier to get
a more exact overlap. Below is the final result:
Final overlap - brightness is matched,
and vertical piece is shifted slightly
to the right.
If all pictures are taken using the same shutter speed and
magnification, you will never have such a vivid brightness disparity.
Sometimes the images will require no touching up, and will overlap
seamlessly.
The final process is to continue this overlapping until the
entire moon is revealed. This final picture should be placed in a
black background and sent to a professional printer. You should
determine the overall size of the poster by finding the largest size that
still prints at near photo-quality. A second poster can be made using
the original image enhanced with text - you can label all the craters and
surface features, and put in a nice title. |
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