Capturing and Processing Mosaics

Part I
The Plan

Part II
Part III
Sub-Frame Processing

Part IV

Part V
Assembling the Mosaic in Photoshop

Part II - Acquisition

There are a couple of tools at your disposal that will make acquisition as simple as any other image.

First, remember the mosaic objects that TheSky created.  To align you telescope with each panel of the mosaic, you can simply issue a Go To each mosaic panel.  Click on, or search for "Mosaic A1" and issue a Go To operation.  Not only will TheSky slew to the target for you, but it will also mark this panel so you know you've been there before.

Try it out.  Slew to the "A1" frame.  You will see the "A1" text change to "(A1)".  TheSky updates this notation whenever you slew to one of the mosaic panels.  This can be especially useful if the acquisition of the mosaic spans more then one night.

If your mount is not very accurate, you should do something about it.  If you cannot Go To each frame with enough accuracy you can run into problems with the frames not overlapping enough.  This will result in gaps during your alignment phase.  In order to achieve better accuracy, you should perform a Plate Solve, or Image Link, of your image.  This function will give you the exact coordinates the telescope is pointing at.  A quick Sync operation on the coordinates and then a Go To the mosaic frame again should give you a high enough degree of accuracy for the mosaic.

It is not very difficult to completely automate the acquisition of a mosaic, including these subjects discussed so far, by using my CCD Commander software.  Below is a screen shot of CCD Commander showing a portion of my plan for the Virgo Cluster mosaic.

At the top of the list is a "Move to" function (the same as a Go To) that moves the telescope to a nearby bright star. 

Next is a function to execute a Plate Solve, mount Sync, and a ReSlew to the original coordinates.  This ensures a high degree of accuracy for each mosaic frame.

Then a Focus routine is initiated to ensure no focus shift occurred since the last frame.

The next item in the list calls for the telescope to move to the "Mosaic A2" location.

And finally, the frame is imaged 9 times at 300 seconds each exposure.  The exposures are auto-saved (AS), auto-guided (AG), and the autoguider is dithered after every exposure.

This process is repeated for the additional frames.

CCD Commander allowed me to image the 9 frames of the Virgo Cluster unattended.  I slept during the acquisition and had 81 images in the morning ready for reduction, alignment, and processing.

Previous: Part I - The Plan
Next: Part III - Sub-Frame Processing

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