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f/5 or f/8 newtonian?
I'm looking at an Antares 6" f/5 newtonian and an Orion 6" f/8
newtonian. Both have parabolic main mirrors, but the Antares is said to be 1/10 wave, while the Orion doesn't say anything like that. Can I assume the Orion will give better on and off-centre sharpness due to it's higher f/ratio? Or will the Antares, despite being much faster, be just as sharp on and off-centre because it's 1/10 wave? Thanks. |
#3
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f/5 or f/8 newtonian?
I don't know the quality of the Antares scope. I have used a Telescopics
6"f/5 Dob for many years and find it is a great scope, owing to its wide maximum field of view, a big advantage, and its ability to take high powers for the moon and planets. It is a very compact and easy to use scope, another big advantage. Owing to the large (almost 3 degree) maximum field with a low power eyepiece,, it is comparatively easy to find things, ar huge advantage. I consider this focal ratio to be a lot better than f/8 in the 6" size. I believe that the main reason the f/8 became a standard for 6" Newtonians is that it is a lot easier to for an amateur making his first scope, to grind, figure and polish than a shorter focal ratio would be. I got a good mirror in the scope I got from Telescopics, now unfortunately long defunct, and then I had it refigured to near perfection by Richard Wessling, of the Pines Optical Shop in Milford Ohio, which has proved to be a very good investment.. If you find you don't like the Antares mirror quality, you can always have it refigured to superb quality by someone very good, such as Wessling or R.F. Royce. My view is a minority view, however. Most people accept the 6"f/8 standard as being preferable. I feel this is largely tradition but they like the larger coma-free area in the (smaller maximum) field of view an f/8 provides. Hope this helps, Bill Meyers Patrick wrote: I'm looking at an Antares 6" f/5 newtonian and an Orion 6" f/8 newtonian. Both have parabolic main mirrors, but the Antares is said to be 1/10 wave, while the Orion doesn't say anything like that. Can I assume the Orion will give better on and off-centre sharpness due to it's higher f/ratio? Or will the Antares, despite being much faster, be just as sharp on and off-centre because it's 1/10 wave? Thanks. |
#4
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f/5 or f/8 newtonian?
You will be giving up some true field, but still have a respectable
amount. Only if you use the same eyepieces. Use longer FL's and still get a good field. Clear, Dark, Steady Skies! (And considerate neighbors!!!) |
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f/5 or f/8 newtonian?
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#6
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f/5 or f/8 newtonian?
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#7
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f/5 or f/8 newtonian?
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#8
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f/5 or f/8 newtonian?
Pat
Id go with the longer focal length scope. Its true that you can get a very nice mirror at f5 but at f8 your chances of getting a good mirror go way up. Plus if you do any planetary work the extra focal length is nice for magnifications sake. Rich On 19 Sep 2003 07:50:41 -0700, (Patrick) wrote: I'm looking at an Antares 6" f/5 newtonian and an Orion 6" f/8 newtonian. Both have parabolic main mirrors, but the Antares is said to be 1/10 wave, while the Orion doesn't say anything like that. Can I assume the Orion will give better on and off-centre sharpness due to it's higher f/ratio? Or will the Antares, despite being much faster, be just as sharp on and off-centre because it's 1/10 wave? Thanks. |
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f/5 or f/8 newtonian?
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#10
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f/5 or f/8 newtonian?
Thank you....that's pretty much what I thought. I like the idea of the
f/8 better too, but my problem is that my EQ3-2 mount isn't sturdy enough to hold it, so I might have to get the f/5. In the typical parabolic, 6", "1/10 wave" f/5, will coma and astigmatism be unacceptable, or not too bad? If it's not too bad, I won't mind. |
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