Dithering and Guiding

 

APT can communicate with various guiding programs and devices in order to monitor and control the guiding. Important purpose of this communication is to provide dithering.

 

Dithering are gentle random changes of the telescope position between the exposures. By this the celestial objects are placed on slightly different positions on every image while the sensor defects like hot/cold pixels, dust signs or banding noise remains on constant or almost constant places. During the images stacking the stars are detected and all frames are aligned by the found star positions - this means that the objects become constant and while defects become random. All major stacking applications for image post-processing provide methods based on "sigma clipping" / "kappa-sigma clipping" pixel rejection. These methods exclude the random data and preserve the constant signal. As a result in the stacked image there will be much less defects and noise. More images you use in the stack more noise and defects will be removed. In order the sigma clipping to be effective there is need to use at least 6 light frames.

 

The author's personal opinion is that good amount of images (10 or more) makes dark frames unnecessary. Making darks is quite time consuming and very tricky process, especially for DSLRs where the imaging sensor temperature is not accurately controlled. Also (again personal opinion) darks applying results in loosing the very faint details in the final image.

 

No matter if you are applying darks or not, dithering is powerful technology is it is highly recommended to use it. The time needed to make dithering depends on the mount and the desired distance, but in most cases it takes less than a minute - quite small price for the benefits it gives.

 

Usually the dithering is made by your guiding program/device and there is no need to make dedicated connection to the telescope in APT if you don't want to use other features that require mount control.

 

APT Dithering is special feature made to provide dithering when there is no guiding because your mount is high-end (ASA, 10Micron and etc.) or when you are using short focal length lens or telescope. APT Dithering uses a mount connection to make the needed random position changes between the exposures.

 

APT Pulse Dithering is other special feature made to provide dithering using pulse guiding commands for self guided mounts like Meade StarLock, self guiding solutions or mounts like SkyWatcher StarAdventure, AstroTrac and etc. In this case the Dithering Distance defines the maximum pulse duration in milliseconds. The value is multiplied by 100. For example Dithering Distance = 5 means up to 500ms pulse.

 

APT has powerful Dithering System that is able to synchronize exposures and dithering even in multi-camera imaging setups. See Multi-camera Dithering / Synchronization section.

 

Supported are the following guiding solutions:

 

 

When MGen3 connection is made, APT acts like server which can be used by other applications (like virtual handset) to connect to the device in same time.

 

There are several requirements for the MGen2 usage with APT: