這類簡易 goto mount 雖有 polar/ eq mode
BUT 看拍得圖還是不好
http://www.cloudynights.com/item.php?item_id=2740DETAILED ASTROPHOTOGRAPHY TESTING
. The goal is to have a highly portable drive that is accurate enough to take 2 minute exposures with my Canon 20Da and 200mm lens (plus the wider angle lenses which require a LOT less tracking accuracy).
So one night I set up the mount in �equatorial� mode by simply tilting the mount and locking it in place. Polar alignment is not quick, but quite effective.
=> Meade EXT 90 和 celestron next4SE 也是都有 eq mode
You roughly point the mount to Polaris, point the camera toward Polaris, align on one bright star, align on another bright star in another part of the sky, then press �enter.� The display tells you how far off of the true north celestial pole both in altitude and azimuth (albeit using confusing terms like �Altitude: 82mins higher� � does that mean too high or that I need to go higher?). Adjusting altitude is easy, just a few turns of the tilt screws. Azimuth changes are tough, as you have to carefully pick up the tripod and rotate either easterly or westerly by a tiny bit. This iterative operation became easier for me once I found out that my 200mm lens gives a 4� altitude x 6� azimuth view of Polaris. So after the 3rd iteration, when the mount told me I was a degree too high and two degrees too west, I could look through the camera to monitor my adjustments. It might have been funny watching me crane my neck to peer through the viewfinder as I hunched over the tripod, attempting to carefully rotate it. I stopped the process once I was aligned within a degree of the pole. The polar alignment took a half hour.
I took a variety of 30 second exposures with the camera, and the results were pretty good. Most shots had very good tracking, with pinpoint stars (see Betelgeuse below).
However, when the camera was pointed near the zenith 天頂 (the Pleiades),
there was a large tracking error in the R.A. I conclude that this is simply a counterbalance error
� the drive is slipping. So I have ordered the optional iOptron counterweight which should fix the problem.
=> 200mm 靠天頂會有 tracking 問題 ..有一說這類GOTO
或者如 mead ext 都要重槌來平衡
不過 smartstar_A 另頭如果改成可接相機不是更方便 => 好像 mini tower 就是
smartstar-A ebay 特價 U$399.. 萬一EQ MODE fail ..當一般 goto 應該也OK 吧..
List Price: $756.00
Price: $399.00
You Save: $357.00 (47%)
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