Astrophotography Tips And Tricks
Cosmology 101 Items',
Learn from these smart tips and hints from other amateur astronomers. These
tips are not guaranteed to work for you, but hopefully you'll learn a
thing or two.
Lunar/Planetary Photography With Short Focus Telescopes
Align Your Webcam
Long Exposure Photography
Celestron NexImage and Puppy Linux
Title: Lunar/Planetary Photography With Short Focus Telescopes
If you've attempted lunar and/or planetary photography with a short focus telescope, you've probably encountered the same problems I have encountered.
First, short focus telescopes need to have an increased effective focal length in order to give enough magnification for high resolution photography. The typical techniques are to use eyepiece projection or Barlow lens projection. I use Barlow lens projection with a homemade or Celestron NexImage web cam astrocamera. This provides a simple system that just slips into the focuser and gives me enough magnification for some very nice images.
Second, it's difficult to get critical focus with a short focus telescope, especially when trying to monitor focus when viewing an image on a computer screen. Short focus telescopes typically have very sensitive focusing because of the small depth of field. Recall how much more is in focus in a camera viewfinder when the aperture stop is f/22 vs f/2. The same holds for telescopes.
To help reduce that problem and achieve sharp focus, I use the following procedure. I get the best focus I can at full aperture. Then I slip a 5 inch diameter aperture mask over the end of the telescope, make any necessary camera gain adjustments, and finally take the picture. Stopping down from 6 inches to 5 inches changes the focal ratio from f/5 to f/6. This is enough of an increase in depth of field to assure sharp focus, even if I was a wee bit off when trying to achieve focus.
Yes, I've reduced the theoretical resolution by going from 6 inches to 5 inches, but a sharply focused image through 5 inches of aperture trumps a poorly focused image through 6 inches of aperture.
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Title: Align Your Webcam
If you've tried astrophotography with either a web cam conversion astro-camera or a commercial web cam astro-camera such as the Celestron NexImage, then no doubt you've occasionally had trouble getting your target to show up on the computer screen. The moon is pretty easy, but getting a planet in the narrow field of view of a web cam astro-camera can be a challenge. In additional to the narrow field of view of a web cam, a badly out of focus planet may not be easy to notice on the computer screen even if you happen to pass over it.
Here's a couple of techniques I use to make the task easier.
If the moon is up as well as the planet I want to photography, I first get the moon in the web cam field of view. That is, get it to show up on the computer web cam application. That's pretty easy, in that even if the moon is quite out of focus, I can tell I've gotten it into the field of view. Then I focus the telescope on the moon, and take note of
where the moon area on the computer screen shows up in the finder telescope. If I'm using a telescope that has an easy to adjust finder, I tweak the finder alignment to put the cross-hair or dot on the moon region that's showing up in the web cam.
If the moon isn't up, I point the telescope at a streetlight a few blocks away. I don't pick one too near because the focus difference between a close streetlight and the target distant planet may be so much that the planet wouldn't show up well on the computer screen when I go planet hunting. A streetlight is also a bright enough target that I can tell if I run across it by monitoring the computer screen. Then, as with the moon, I focus on the streetlight and tweak the finder, or take note of the area of the finder that's in agreement with the web cam.
Now I can usually find a planet. I know pretty accurately where in the finder to position the planet for it to show up on the computer screen, and the telescope is in focus well enough so that at least a blob of light will show up when I cross over the planet. Once I can get that blob, I can adjust the web cam gain and fine focus the telescope.
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Title: Long Exposure Photography
This long exposure hint is pretty simple, but some of you may not have tried it.
I occasionally do some piggyback photography with my modest astronomy equipment. I mount a 35mm camera onto my 6 inch Newtonian, which has a clock driven mount. But my mount doesn't have a drive on both axes of the equatorial mount, and has only a clutch mechanism on the RA axis with an adjustment knob. So, even though I try to be meticulous in aligning the telescope before I begin a photographic session, some guiding errors occur.
Since I can't make precise and smooth adjustments to the guiding, I simply slip the lens cover onto the camera lens, then do the manual adjustments to put the object of interest back into proper position. Then I let the telescope track for a few seconds to be sure all is well. Finally, I remove the lens cap and let the exposure continue. I've achieved very good results with this simple technique. So don't be put off if you can't afford an auto-tracking system, just try this simple technique.
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Title: Celestron NexImage and Puppy Linux
If you would like to use a web camera / astro camera conversion for doing some really neat astro imaging, but you are held off because you're a Linux user, here's some good news. Puppy Linux has a utility called guvcview (it's in the menu system) that can operate a wide variety of web cameras. It happens to work with one of the most popular web cam conversions around, the Celestron NexImage Solar System Imager.
If you don't happen to use Puppy Linux and can't find guvcview for your Linux system, consider just booting a recent version of Puppy Linux (like Lucid Puppy Linux 5.2.8) from CDROM, and running guvcview that way. From there you can operate and save data to a flash drive if nothing else, and be on your way to some great astrophotography.
You can read my Celestron NexImage Review my Puppy Linux Review to get more information.
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