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Focal length & focusers


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There are a lot of experienced Newtonian users here and the subject of collimation seems quite common.On a fast Newt say f4.5-4.7 with a production focuser(maybe not so tight or accurate) I can see where focuser slop may contribute to innacurate or unrepeatable collimation.Is it possible that visual image degradation will present itself because of this factor?And do most experienced fast Dob owners run premium focusers?

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Hi Gerry - I would agree collimation becomes more critical the faster the scope. A self centering adaptor is a must for aligning the mirrors to avoid any slop. A lot of folks change the standard focusers that come with their scopes for a higher grade focuser like a "Moonlight" - I see a lot of those on big fast dobs and fast imaging refractors. It's also important to ensure the collimator itself is collimated too. It's largely personal which collimator one uses - I have a "Hotech" premium collimator but there are other good ones and several different techniques. :)

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The self centering adapter like Glatters parallizer looks good so that I can run the 1.25" eyepieces "centered too,but as the focuser is moved the slop must contribute to image quality-lets say you're collimated but not excatly in the center of the sweet spot-I think fast ratio's s are just over 1mm or so-I'd have to look again-with the collimation piece centered alls well until the focuser is moved and then possibly everthing is in and around or out of the sweet spot at times.The need for a premium focuser becomes apparent for fast scope as you say.I have never collimated a scope but am slowly understanding the optical design of a Newtonian and also how the mechanical structure contributes to the real world operation of the scope.The Hotech looks good as it self centers as well.I'm limited in solid tube Dob choices to the mass produced units for now and wish that a f6 10" was available.With stock focuser I may opt for the 8" f6,more portable & if it takes a hit maybe everything will stay in the sweet spot.I love learning about how things work and then using them in the field.And so after using my frac I still am amazed at how faint some objects are.I wish Orion Optics U.K. were available here,they have a lot of great options.With your 300p flextube...how do you like it overall?

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