[Astro_Bot]

Originally Posted by Rodstar

BOTTOM LINE - The views through the SCTs I used were quite obviously inferior to the views through the same or similar sized dob. Some nights I ended up pretty upset, wondering why the f..k I had spent $5.2K for my LX200 when Mike had spent only $900 for his, and the views through his scope were quite obviously superior. Galaxies that were a mere blob in my scope were more clearly defined in his scope. Doubles were more clearly split in his scope etc. etc.

And yet my experience, and that of many others, is quite different.

An SCT has a longer focal length than a dob of similar aperture. This will result in the SCT showing a higher power view (smaller portion of sky) than a dob with the same eyepiece. The problem is that the quality of that higher power view is inferior.

Who said you had to use the same eyepiece?! I can comfortably get 1.1 deg TFOV with, say, a 41mm Panoptic and there's not much to see that's wider than that. At the other end of the scale, high power views are more difficult on a Dob - try looking at Jupiter on a good night at 300x in a 12" Dob and see how often you have to "chase it" by moving the Dob or suffer the "step stair" tracking at that power. It's not a comfortable viewing experience! The smoothness of tracking of an SCT on say an EQ6 is outstanding (but pretty good even on a fork mount) allowing a comfortable and lengthy study of any target at high power (seeing permitting). The high-power view is not, in my experience, inferior in any way. In fact, in my experience, it's superior, especially since you can focus on it for such a long time. That's not to say that there aren't better-than-average Dobs out there that can't give a good high-power view, but it's not, typically, going to be easy or comfortable.

SCT's suffer badly from dew, as their design involves glass against the open air. This can be reduced with a dew shield, but even still, this is far more vulnerable than having the primary mirror at the base of a dob.

At a noteably dewey star party last year, where no-one had dew heaters, only home-made dew shields, my SCT was the "last scope standing" with all others, including ALL of the Dobs, being dewed up well before mine. You simply can't make that generalisation and I think it's a little disingenious to claim that dew affects SCTs more than Dobs when a $10 DIY dew shield is all that's needed to turn the tables. Why do so many people add fans if Dobs are so good with dew? My experience (and not just based on that night) is that typical Dobs have no advantage at all when it comes to dew. Then there's the chipboard base's susceptibility to moisture ...

I found the mirror shift from using the focuser very irritating, requiring constant refocusing.

Mirror locks, microfocusers, zero-image shift focusers, crayfords, etc., have well and truly addressed that problem. On the other hand, there are plenty of shaky Newtonian focusers (on mass-produced Dobs) out there. I don't think you can claim a typical Newtonian's focuser as any kind of advantage. And there's no shortage of people who want to upgrade the focuser on their stock-standard Dob.

If you really want to talk about irritating, how about having to much more frequently re-centre your target or hunt for it in the first place (though, truth be told, some people enjoy that challenge)? And what about people bumping the Dob at a star party? That's not a problem you'll ever have with a sturdily-mounted SCT.

If I was looking to purchase a 10" for visual use again, and was planning to keep the scope I purchase for more than a year or two, I would (without hesitation) go for a dob over an SCT.

You're welcome to your choice of course. But people who've grown used to SDMs, especially an amazing scope like the Mary Rose, might not be in the best position to accurately recount how a typical GSO/Bintel or Skywatcher performs. Again, I'm not saying they're bad, but is it possible there's a little cognitive bias going on? You and John love your SDMs (and quite rightly so). Perhaps that's colouring your memory of cheaper, mass-produced Dobs? Just a suggestion.

I'm seriously not making it up when I say that my SCT is frequently regarded as "best on the field" against GSO/Bintel and Skywatcher Dobs. I have no doubt it wouldn't hold a candle (visually) to any SDM, but then that's not what Richard was asking about.

This is quicky devolving into tit-for-tat and a preference argument. I think there's little value to be gained in arguing further.

Poor Richard is probably wondering what he's let himself in for! We're much nicer in person. Really!