Meade #1220 Field De-rotater

[funoooo]

有没有兄弟用過此配件，好似用了佢就經緯 Goto 都可拍照。Work 唔 Work "嫁"？ [鬼點子] [鬼點子] [鬼點子]

[鄧登凳]

有没有兄弟用過此配件，好似用了佢就經緯 Goto 都可拍照。Work 唔 Work "嫁"？ [鬼點子] [鬼點子] [鬼點子]

會不會買個wedge變做赤道式好過

(意思是即使電腦控制, 一個馬達引致的誤差, 應比三個馬達的少)

[funoooo]

有没有兄弟用過此配件，好似用了佢就經緯 Goto 都可拍照。Work 唔 Work "嫁"？ [鬼點子] [鬼點子] [鬼點子]

會不會買個wedge變做赤道式好過

(意思是即使電腦控制, 一個馬達引致的誤差, 應比三個馬達的少)

wedge 對極軸好難.

[鄧登凳]

wedge 對極軸好難.

照Meade自己所述, 又不似是太難。
(見 http://www.meade.com/manuals/lx200/apxb.html )

不過我是紙上談兵, 有錯請指正。

[funoooo]

wedge 對極軸好難.

照Meade自己所述, 又不似是太難。
(見 http://www.meade.com/manuals/lx200/apxb.html )

不過我是紙上談兵, 有錯請指正。

因為我是超級懶人。 [萬年奸臣]

[funoooo]

找到一份由官方槍手(寫手)寫有關 De-rotator 報告。說到非常精彩，好似接近天下無敵。
http://www.meade4m.com/cgi-bin/article.cgi?ID=464

Conclusion: Wedges and polar alignment play an important role in astrophotography for fork-mounted telescopes. I have shown here that a de-rotator is a viable option for the amateur, and does in fact work very well when used properly with a little patience. With any new tool, it may take a few tries before one can effectively use a de-rotator for streak free, yet awesome, photographs.

[funoooo]

The advantages of a field derotator are that you have one less heavy piece of equipment to take out into the field and assemble (an equatorial wedge) and you eliminate the extra time and effort needed to polar align the scope and equatorial wedge. In addition, you can image near the north celestial pole and the southern horizon with the field derotator. If you have an electric focuser, flip mirror system, and camera stacked on the rear of your equatorially-mounted scope, the equipment stack might be long enough to hit the drive base of your scope before the scope reaches the area around the pole. Since the field derotator works in the altazimuth mode, where the fork arms point straight up at the zenith, aiming at the celestial pole 30° or 40° above the northern horizon is not a problem. Also, with an equatorially-mounted scope, the front end of optical tube can often hit the drive base of the scope before the optical tube can be tilted low enough to aim at the southern horizon. Again, the altazimuth orientation of the scope using a field derotator eliminates this possibility.

Some of the drawbacks of the field derotator involve these very advantages, however. If you have a long enough equipment stack on the back of your scope – electric focuser, flip mirror system, camera, and now also a field derotator – you may have problems aiming the optical tube at the zenith with the field derotator in use. Whether your camera hits your scope’s drive base depends on how much swing-through clearance your scope has and how much equipment you feel you need to stack on your scope’s rear cell.

A more significant drawback might be the loss of your scope’s PPEC (Permanent Periodic Error Correction) when the field derotator is used. PPEC only works when the scope is equatorially-mounted on a wedge. It does not work in the altazimuth mode. If your scope has a drive system with low periodic error in both drive chains, the field derotator will permit perfectly acceptable long exposure images. If, on the other hand, your drive has enough periodic error to show up as slightly streaked stars in images taken in the equatorial mode (even if the errors can be eliminated by training the drive using the PPEC system), those errors will also show up using the field derotator. If you have reservations concerning the accuracy of your scope’s drive system, consider using the appropriate equatorial wedge and training your scope’s PPEC system rather than investing in a field derotator.

In the end, neither field derotator nor equatorial wedge is the perfect solution. You have to weigh the advantages and disadvantages to you of a field derotator over an equatorial wedge – weight, setup time, equipment stack and PPEC issues, etc. – in order to decide which route to take to reach your astrophotography goals.

[sn-10]

For a perfectly aligned GEM, only the RA motor/gear is working; in the fork mount, both axis are moving at all time, thus higher error. Adding a derotator, you are adding a 3rd variable to the system, introducing more error.

After all, a fork mount is not significantly lighter anyway.

[PTS]

For a perfectly aligned GEM, only the RA motor/gear is working; in the fork mount, both axis are moving at all time, thus higher error. Adding a derotator, you are adding a 3rd variable to the system, introducing more error.

After all, a fork mount is not significantly lighter anyway.

Are you talking about altazimuth fork mount?
A fork mount can be equatorial.

PTS

[funoooo]

For a perfectly aligned GEM, only the RA motor/gear is working; in the fork mount, both axis are moving at all time, thus higher error. Adding a derotator, you are adding a 3rd variable to the system, introducing more error.

After all, a fork mount is not significantly lighter anyway.

Yes, Sn-10. You are right. There are 3 different motor moving will generate and build up the error. However, that will be the other option for those, who don't know how to make the folk arm polar aligment.

[funoooo]

The Iceinspace review.
http://www.iceinspace.com.au/index.php? ... 55,0,0,1,0