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Thanks Mark, but no Barlow used - on the contrary, I used a focal reducer as this was my 16" planetary Dall-Kirkham that has a prime focus of 6.5m. The Dall-Kirkham configuration has quite bad coma - which is not a problem for planetary imaging - so I designed a focal reducer that also corrects the coma but only has a useful field of about 10mm diameter and gives a focal length of 4m.
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