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Most SCT users doing webcam planetary work will use a 2x or 2.5x barlow or powermate, taking your effective focal ratio to f/20 or f/25, which is pretty much ideal. With 5x your light drop off will require a glacially slow frame rate, longer exposures that won't freeze the seeing well, or a very much underexposed histogram. The 2.5x powermate works well but this particular powermate has an unusual characteristic you need to watch out for. All barlows and most powermates will have an increased image scale (beyond the 2x) if you insert extra space between the barlow and the webcam with an extension tube. However the 2.5x powermate actually has a decreasing image scale with further distance. Somewhere on the Televue website there's a graph of the effective magnifying power of each with increasing distance.
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