red dwalf Posted July 25, 2009 Share Posted July 25, 2009 hi all,can i ask, is it better to have a short focal length scope or a long focal scope for imaging planets.i have a skywatcher 5.1" 650 focal length f/5 newtonian and a 6" 1500 focal length f/10 celestron 6se.i asking which would be best to use with a webcam ? Link to comment Share on other sites More sharing options...
GazOC Posted July 25, 2009 Share Posted July 25, 2009 Long focal lengths are better for planets, the SCT is the one to use...) Link to comment Share on other sites More sharing options...
brianb Posted July 25, 2009 Share Posted July 25, 2009 Long focal lengths are better for planets, the SCT is the one to use...)And even then you'll probably need a barlow, at least once you get experience. You need to work at f/20+ to wring out all the detail that the objective can resolve though that does take good seeing, especially on lower surface brightness targets (Jupiter, Saturn). Many of the really great images taken in excellent seeing are at focal ratios around f/40. Link to comment Share on other sites More sharing options...
Doc Posted July 25, 2009 Share Posted July 25, 2009 You could do with a X4 powermate Rob. Link to comment Share on other sites More sharing options...
red dwalf Posted July 25, 2009 Author Share Posted July 25, 2009 Thanks chaps,I do have a 3x TAL barlow so will try this tonight if the clouds don`t roll in, would i also be better when imaging to not use the diagonal when attaching the barlow and webcam ? Link to comment Share on other sites More sharing options...
brianb Posted July 25, 2009 Share Posted July 25, 2009 would i also be better when imaging to not use the diagonal when attaching the barlow and webcam ?Yes, the less in the way the better. Link to comment Share on other sites More sharing options...
GazOC Posted July 25, 2009 Share Posted July 25, 2009 Thanks chaps,I do have a 3x TAL barlow so will try this tonight if the clouds don`t roll in, would i also be better when imaging to not use the diagonal when attaching the barlow and webcam ?Yes, but you may find you don't have enough focus travel without the diagonal as the barlow will push the point of focus "outwards".Its worth a try though, SCTs have a very good range of focus so you might well be OK. Link to comment Share on other sites More sharing options...
brianb Posted July 25, 2009 Share Posted July 25, 2009 Its worth a try though, SCTs have a very good range of focus so you might well be OK. I'd be amazed if you're not.For those scopes that do have "too much backfocus" issues, get an extender tube to use up the extra length. Link to comment Share on other sites More sharing options...
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