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F/4 Collimation

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Posted by Dean Warlin on October 30, 2003 00:56:55 UTC

At this fast of f-ratio the collimation becomes extremely important (I have a 13.1" f/4.5 Dob and I've learned this in a hurry) for planetary viewing. Also, a fast reflector tends to develop "coma" where the stars toward the edge of the field of view become elongated, especially in wide field eyepieces - this is a problem that has to do with the nature of parabolic mirrors. Televue makes "Paracorr" which corrects this parabolic abberation, for just under $300. As far as eyepieces, if you have a drive on your mount, you might want to look at orthoscopics for a smaller field of view on planets, the Monocentrics reviews are good but they are pricey eyepieces. I use a 4mm Radian or a 7mm Siebert/Barlow combination for planetary viewing, they don't give as good a view of Mars as my 8" f/6 Dob did or my 70mm Orion refractor does, I'm still working on perfecting my collimating technique on the 13.1". For DSO and star viewing I use wide angle eyepieces and notice the coma, but I can live with it for now as the views are so spetacular.

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