Originally Posted by Gem
Does anyone here use a field derotator to do casual imaging with a dob? Does it work ok? Is it a viable option for the casual imager?
Gary Kopff here from Wildcard Innovations.
We get to correspond with a very large number of scope owners from around
the world so have a good feel for what is out there.
Field de-rotators on Dobs are very rare and those we hear about tend to be
installed on larger, premium Dobs. On Dobs in the 10" to 12" range, they
are rarer still to the point I have never corresponded with an owner that has
mentioned owning one.
Taking a step back, even before one uses a field de-rotator, one still needs to
drive the scope in Alt/Az as well.
Tracking Dobs are now commonplace. For example, for scopes in the 14" to 30"
class, servo controllers such as the ServoCAT and Sitech units used in
conjunction with our own Argo Navis Telescope Computer are commonplace.
One IIS member recently installed a ServoCAT/Argo Navis on a LightBridge 12".
Generic tracking Dobs in the 12" and 14" class are also shipping out of the Far East.
However, as mentioned, it is rare to hear of owners adding field derotators
As I posted here on IIS some time back, despite the limitations of field rotation,
there are plenty of enthusiasts out there achieving stunning results with
autoguiding on Alt/Az mounts using short exposures and software derotation.
For example, check out these images by Johannes Brachtendorf
using an 18" Obsession, Argo Navis, ServoCAT, SBIG ST 9E and software
derotation. As Johannes says, "no platform, no derotator, no adaptive optics".
Also be sure to read Johannes notes on the subject -
So you wouldn't be breaking any new ground if you were to use short
exposures and software field derotation. However, on smaller apertures scopes with
long focal lengths, deep sky objects would still be challenging and so a Dob
in the 12" to 14" class may be restricted to brighter DSO's and the planets for
A key phrase you used is "casual imager". The results using the above prescription
may not be of a caliber to put one in the running for a David Malin astrophotography
competition prize, but they can be immensely personally satisfying.
Equatorial platforms are another solution but have become less common
in recent years.
Hope the above might be helpful.
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia