19/02/12: CCD Focussing

February 20, 2012  •  Leave a Comment

One of the reasons for using a Lakeside focuser is the ability to focus accurately automatically using computer software. I find that using the focuser with the @Focus functionality of CCDSoft works particularly well. Seeing as this evening was again thwarted by low level cloud, I decided to write off an imaging session and spend a little time assessing the abiliy of @Focus to focus accurately. I also wanted to establish the degree of focus shift between the LRGB filters. The Tak FS-102 is good for a doublet apochromatic refractor, but I have noticed a slight shift in the past with my LRGB imaging. I therefore ran a few @Focus routines for each filter and determined that the average shift from Red to Green and Blue was 23 units on the Lakeside Focuser. This corresponds to a focus shift of approx 138 microns. Knowing this, my intention is to try a little more LRGB imaging, moving the focus manually by this amount for the green and blue subs. I can still run an @Focus routine at the beginning of the evening to check my focus is good at the start. Obviously temperature changes come into it, but it's a start!

I've found that I've tended to concentrate more on the hydrogen alpha imaging lately due to the simplicity of monochrome imaging. Come galaxy season however I want to be LRGB imaging a lot more.


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