The Moon not only is a stepping stone for humankind's exploration of the universe. The Moon also is a good stepping stone for your astrophotography and often the first distant target people shoot.
Getting a tack-sharp, large-scale result like the above 2703x2231 pixel image isn't something that comes easy. Anyone, who has tried to get a close-up shot of the moon from a single shot with a dSLR will recognize that challenge.
Of course, focal length is one important factor to improve the resolution. But in this case, it is NOT the only deciding factor. Instead, the "secret" lies in the method of HOW TO get to this result. You can improve the final result by capturing many images and picking the best of them, or even just the best portions of all those images, to build a composite image.
To better understand the problem, you have to consider how the Earth's (turbulent) atmosphere can get in the way of (terrestrial) observation. You don't need a high- powered telescope to see that -- grab your SLR & 300mm zoom and you already can see the image of the moon being distorted and looking "wobbly" -- and it can look much worse than this : watch?v=PbGFN1rv2qw
One way of improving the quality is to collects just a whole lot more data -- and you can use simple algorithms to average out the results or you can use more sophisticated pattern-matching algorithms to correct distortions and align images. Furthermore, these algorithm break the image into many small pieces and measure the quality (sharpness) of each piece, match the various pieces from all the (hundreds) of frames you captured and later blend all that into a singlle high-res still image.
That sounds like an awesome and fairly expensive piece of software, doesn't it ?
Awesome - YES. Expensive -- NO !! The software I am using is AVISTACK and it is FREEWARE. (small nagging screen) -- there is the small issue of acquiring the hardware -- that usually isn't free.
The setup I use
- you can use any telescope, use prime-focus or par-focal and attach the camera to an eye-piece. The larger the magnification, the more time it takes to cover the moon. Of course you gain more details
- you want a real VIDEO camera, not a SLR or phone -- important is the ability to record UNCOMPREESED (AVI)-data. Since the moon is bright, you can achieve 10....50FPS sampling rate, depending on your computer HW, the camera and the resolution. My setup uses 15FPS (1280x1024, 8bit B&W) UNCOMPRESSED AVI. And I emphasize UNCOMPRESSED. MPG and others eliminate the tiny dots and include compression artifacts because they think stars are noise. You don't want to use a LOSSY compressions for this.
Recording uncompressed AVI generates ~ 1GB / minute ==> you better have a large (and fast) TEMPORARY storage. An external USB-drive make file transfer easier and avoids long wait times to copy the files from your out-door laptop to the PC for actual processing
- To capture all those sequences, you need a program to control the camera, perform pre-programmed exposure sequences, etc, ... and most cameras come with some SW to do that.
SHARPCAP is a Freeware tool, similar or better than the tools I have seen in the camera bundles
- With a sufficiently large HD, you can capture a single 30-minute stream of AVI video. Or you can capture 30 x 1-minute streams. Or 60 x 30sec streams. What is the difference ?
For once, the 30min file will be 30GB but the SD-card you use to transfer files only supports files < 2 GB (FAT32 limitation)
If anything goes wrong, you may loose 100% but only 1/30 or 1/60 if you "Divide & Conquer" : processing more but smaller files is more efficient
- The 2GB file limitation was the first big surprise I encountered
Transfer times from the outdoor laptop onto SD-card and from ther onto the desktop PC were as long, or longer, than actual image capture. Having USB3 sure made a difference.
- AVISTACK turns one video stream into one high-res TIFF or JPG. And it does align & merge the images within the same stream, it doesn't do anything beyond that.
- After AVISTACK generate 30...60 still images, I use AUTOPANO PRO (you may choose free PTgui) to align & stitch together the final result.
Sometimes it is "good" to have a telescope mount that's not accurately aligned because the drift provides a "natural" & slow-moving motion you can use to scan stripes of the lunar surface. Oncee that slow drift is complete, you still need to slew to a new start position for the next pass.
While I have seen good tools to position the mount among the stars, I haven't yet seen (or searched for) a tool to analyze the moon's map and assist in navigating the lunar surface.
The technique I described here also can be applied to capturing (color) images of Jupiter & Saturn. The moon is a lot bigger & brighter, making it a good starting point to learn the technique. And once you mastered mapping the lunar surface you can go on and scout the outer planets ...
As you increase magnification -- for example by shooting through the eye-piece -- the benefits of the stacking approach become even more important.
LINKS to dowloads :
SharpCap2 : www.sharpcap.co.uk/sharpcap/downloads
FireCapture : firecapture.wonderplanets.de
AVIstack : www.avistack.de/download.html
VirtualDub : www.virtualdub.org
Handbrake : handbrake.fr
TEncoder : sourceforge.net/projects/tencoder
VLC player : www.videolan.org/vlc/index.html
DEEPSKYSTACKER : deepskystacker.free.fr/english/index.html
REGISTAX6 : www.astronomie.be/registax/download.html
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