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Originally Posted by ausastronomer
Pure physics determines that a SCT cannot equal the optical "visual" performance of an equivalent aperture newtonian, or refactor.
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Pure physics doesn't build affordable telescopes. Most people are limited by more practical concerns like size, weight and cost.
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The performance of Rod's scope was partly due to mediocre optics and partly due to the cooling issues of a closed tube design.
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Sure, an SCT takes longer to cool. I put mine out at sunset and by the time I've setup and finished alignment, it's had about 2 hours of cooling under a clear sky - quite enough. It's no impediment at all in a typical evening's viewing.
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My 10"/f5 GSO newt, which has a great mirror in it for an $800 scope will pull 500x on night of good seeing. My 10"/f5.3 SDM with Suchting primary will pull 675x (5mm Pentax XW + 2.5x TV Powermate) on a night of good seeing. How many mass produced SCT's can do that?
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In my 10" LX200-ACF, I've had 420x on a night of good seeing and could have gone higher if I had a shorter focal length eyepiece (the image was crystal clear and steady at that power). We all know that these magnification limits are primarily determined by the seeing, not the 'scope, in any largish aperture used near sea level.
I've looked through 10" and 12" dobs of GSO and Skywatcher origin at many a star party and really can't say I'm impressed, even with the larger 12" aperture - I'm not saying they're bad, but they're not as good as you claim them to be. On the other hand, at
every star party I've been to, I receive complements on the relative quality of the view through my SCT and frequently hear things like, "Wow, you've got the best view here". I don't call that "mediocre optics".
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That's not to say SCT's don't have their place. They make an excellent all rounder if you plan to do both visual and imaging with the one telescope and they offer a portable, transportable package.
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They do make an excellent all-rounder, but you don't need to do imaging to make that the case - they're a good all-rounder just for visual. And some people hate the diffraction spikes of a Newtonian with a vengeance.
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If storage and transport are not a concern ...
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There's the rub. Storage and transport are a concern for most people - not so much for many of the posters on this site, who can afford their own backyard or remote observatories, but for everyday amateurs who have, at best, a spare room or corner of a garage and an average car to get around. And heaven forbid if you have to negotiate stairs!
Horses for courses. A Dob is cheaper than an SCT (with mount) of the same aperture. If you can transport it (or don't need to); if that's all you want and you don't mind diffraction spikes, then fine. But don't talk down SCTs on some theory that they will be always be inferior - in mass-produced examples, they are not.