Is Parabolic better than a classic telescope?

[Event_Horizon]

Hi, I've been looking at a new telescope (SkyWatcher Skyliner-200p) and it is available in either parabolic or classic. I read that parabolic reduces the blur on objects being viewed through it, which sounded to me like the parabolic is better. Only the classic is more expensive, so is the classic better or is the parabolic?

Many thanks

[sbooder]

I have never heard of just a classic, thye are often called Sky-Watcher Skyliner-200P Classic 203mm Parabolic Dobsonian Telescope?

[ScottS]

As far as I know, that scope only comes with a parabolic mirror to eliminate spherical aberration. In other words, bring all the light to a common focal point which a spherical mirror will not.

[Event_Horizon]

Oh, ok. I think what has happened is that they're selling the same telescope for two different prices. Thanks for the help!

[NGC 1502]

If the choice is between a parabolic or spherical mirror, it depends on the focal ratio as to which is 'best'.

At F4 to F6 parabolic is needed to be satisfactory.  

At somewhere around F7 to 8 or more, spherical works well because the difference in the optical figure between spherical and parabolic is small enough to ignore.

There's loads more optical theory out there, much of it beyond me, but the above is a reasonable enough explanation without getting too technical.

Regards, Ed.

[michael.h.f.wilkinson]

The exact focal ratio at which spherical is as good as parabolic depends on aperture, and on your required optical figure (lambda/10 is stricter than lambda/4, obviously). In 6" scopes (at some lambda/N, with N a small integer which escapes me at the moment) parabolic was still considered better at F/8, but at F/11 spherical would do (essentially a parabolic and spherical surface would differ by less than lambda/N, I was told). In smaller scopes, faster mirrors could still be spherical