Optec Alt-Azimuth Derotation Server
Camera Field Derotation Software with ASCOM Local Server
What is De-Rotation and Why is it Needed?
While
alt-azimuth mounted telescopes are wonderful for visual observing, they
present a unique challenge for astrophotographers. In order to capture images
longer than several hundred seconds the camera must be de-rotated during
the exposure to compensate for the rotation of the image plane. This rotation
rate is not constant over time but can be calculated based on the right-ascension
and declination of the object, the longitude and latitude of the observer,
and local sidereal time. With the use an alt-azimuth mount, an Optec camera
field rotator, and the Optec Alt-Azimuth Derotation Server, anyone from
the amateur level to the professional astrophotographer can easily capture
high quality images using an alt-azimuth mounted telescope.
The graphic to the right represents the structure of Optec Alt-Azimuth Derotation Server and how it interacts with the ASCOM client application and physical devices. The Optec Alt-Azimuth requires an ASCOM client application. The client app connects up to the rotator shim which in turn connects up to the actual rotator driver. We call it a shim because it does not actually control the physical rotator as a normal driver would. The rotator shim has two functions: it passes commands and data between the client app and the actual rotator driver, and it makes de-rotation move requests to the actual rotator driver. The telescope shim functions in a similar way as the rotator shim. The client app connects up to the telescope shim, which in turn connects to the actual telescope driver; any ASCOM telescope driver can be used. The most important part of the Optec Alt-Azimuth Derotation Server is the arrow that points from the telescope shim to the rotator shim. This arrow represents the passing of the current altitude and azimuth data from the telescope to the rotator shim. The rotator shim uses this data when performing the de-rotation rate calculations.
The Alt-Az Server Status window will always be open when the server
is running and can be used to monitor the progress of
derotation. The windows displays the drivers currently selected, the current
Altitude and Azimuth of the telescope, Position Angle of the rotator and
current derotation rate. The Status window also allows one configuration
value called “Steps per Adjustment”. In some cases the communication latency
between the PC and the connected devices is too great for the derotation
server to run at it’s optimal speed. If this is the case you will see the
Missed Steps number increase. If this occurs regularly, increase the Steps
per Adjustment property by one. This means that the derotation server will
wait longer to make a derotation move but that the move will be larger.
The net rotation over time will be the same but with less frequent adjustments.
If you change the Steps Per Adjustment
property value you must press the
Store Value button for the change to take effect.
Alt-Az Derotation Server Software Installer:
Quick Start Guide:
View the Optec AltAz Server Quick Start Guide. |
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Special Notes:
View the Optec Alt-Az Version Note for Version 2.xx updates |
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