Field de-rotators ???

[Stu Ward]

It's times like these with endless cloud cover that the mind starts to work and makes my wallet cringe.
I've been playing with my dob for some time now taking DSO photos.
Exposure time never more than 30 secs, is there a de-rotator for skywatcher dobs, and would it make that much difference ?

Thanks

Stu

[DavidTrap (David)]

A field derotator needs to spin at precisely the right speed to cancel out field rotation caused by the alt-az mounting of your dob. It would need some means of calculating where in the sky it is looking to know how fast to turn, ie encoders on both axes.

You would also need to track the dob in both altitude & azimuth. This requires fancy electronics to coordinate the slow, smooth movement of three things at constantly varying rates to achieve a static field. Technically thus is possible - most modern professional observatories use this technique, but it's not a viable solution for consumer equipment. Meade do have a derotator for the LX-200 scopes, but I'm not sure if they are still produced and I've never seen an image taken with one posted on the web.

DT

[Stu Ward]

Originally Posted by DavidTrap

A field derotator needs to spin at precisely the right speed to cancel out field rotation caused by the alt-az mounting of your dob. It would need some means of calculating where in the sky it is looking to know how fast to turn, ie encoders on both axes.

You would also need to track the dob in both altitude & azimuth. This requires fancy electronics to coordinate the slow, smooth movement of three things at constantly varying rates to achieve a static field. Technically thus is possible - most modern professional observatories use this technique, but it's not a viable solution for consumer equipment. Meade do have a derotator for the LX-200 scopes, but I'm not sure if they are still produced and I've never seen an image taken with one posted on the web.

DT

Well the dob is Goto, so tracks really well, just need something to cancel out the rotation

Stu

[Merlin66 (Ken)]

On another thread there was similar discussions re the Pixis de-rotator, about $1400........
The Meade only works with an Lx200.

[Stu Ward]

$1400 I might as well buy another scope for AP !!

Suprised that Skywatcher haven't come out with one

[Poita (Peter)]

There is the Pyxis for $1500 or the combined adaptive optics/derotator for $1999. Johannes gets good results with software derotation here http://homepages.uni-tuebingen.de/jo....brachtendorf/
It may be possible to use bartels system and build your own if you are more clever than me, and save some $$
http://www.bbastrodesigns.com/BBAstr...RotatorFocuser

[Stu Ward]

Wonder which software de-rotator he used ?

[Poita (Peter)]

Pretty sure it was astroart