Moon Mosaic using a Focal Reducer - almost!

Posted by XTSee on 22nd March , 2009

Quite a while ago I bought a 0.8x Focal Reducer for my XT10i telescope in the hope that I would be able to obtain a wider field of view when taking astronomy pictures with my SPC900NC webcam.

Unfortunately I couldn’t get the damn thing to focus, even with my Low-Profile Crayford Focuser. It may be just that I need to get an extension tube to increase the focal length, or it might be that the focus is actually shorter than the crayford can go even at its minimum. Not sure really.

So for a while the reducer went unused.

However now that I’ve got a C6 SGT XLT as my second telescope I’ve been waiting for a decent night for viewing, and one evening when there was an almost full Moon I thought it would be an ideal easy target for understanding how to use the focal reducer.

Obviously the first thing to do was get the scope setup, and focus in the normal way with the webcam. With this achieved, next I added the focal reducer to the equation, and then tried focusing.

I was amazed at how many anti-clockwise rotations of the focus knob I had to turn! It needed about 5 full turns before it eventually came to focus, and then I was able to see how much more of the moon the view now covered using the reducer.

Since everything was now setup, it made perfect sense to attempt my very first moon mosaic, so I got the best focus I could, made the best adjustment with the webcam for its various settings; gain, white balance, brightness, gamma, FPS and shutter speed, and then went about making a number of 10 second video captures, repositioning the scope target to take the whole surface of the Moon, allowing some overlap from one image to the next.

Or so I thought!

Moon Mosaic Mistake

Moon Mosaic Mistake

Back indoors I processed each individual capture using K3CCDTools, being careful to try and use the same settings and enhancements for each AVI movie, and then using Photoshop I set about importing each image and overlaying and aligning them, making adjustments to the levels of each image to make them match up as best as I could.

Of course I didn’t realise until I had done this that some big moon mouse had taken a hefty bite out of the cheese. Bugger it, I really thought I had it covered, so to speak.

You live and learn. I’m quite pleased with the level of detail, but I think there’s a few things I need to improve for the next time. The white balance seems incorrect as the colours of the Moon don’t seem right, although this might have been me overcooking some hue/saturation settings in Photoshop. Also I could use some gaussian blur at the edges of each image to give a smoother transition from one to the next.

Click the image to see and zoom into the full size picture.

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