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Hi Tardis & welcome,
I don't pretend to be the font of all knowledge on telescopes, but here goes.
A 16" 'scope theoretically has much better resolving power and will be capable of resolving more detail more easily than your current 8" -- of that there is no doubt.
You will also get a brighter image of planets and much else. So from that point of view, stepping up in aperture to see more detail _on planets_ at least seems like reasonable advice.
With a really well made dob, it is certainly possible to hand track and enjoy a frustration-free view at powers up to about x250. Commercial drive systems are available for dobsonians but are in truth complex and expensive. For example, on my 18" Obsession clone I have an Argonavis and a Servocat which work together flawlessly and produce excellent "visual grade" tracking. With a bit more tweaking and a field de-rotator, I could do imaging as well. However for that level of performance you will have to outlay about $2,600 on top of the cost of the 16" lightbridge bringing the total cost to $5,500- or thereabouts plus eyepieces.
As an alternative, the Mel Bartels telescope-making site has instructions and what-not for a dob drive for somewhat less outlay, but it is very do-it-yourself. Another alternative is a Poncet platform which provides quite nice tracking and these can be home made for a few hundred dollars but some think they are a bit fiddly. Others love 'em.
Having said that, in practical terms, the increase in aperture and thereby the ability to see increasingly fine detail on planets and the moon is very much limited by our turbulent atmosphere (seeing). Assuming the planet is reasonably high in the sky, on a really good night the 16" will show somewhat more detail on Mars. However, during this coming apparition, Mars be close to aphelion (the furthest point from the Sun in it's orbit) meaning it will be pretty small (as viewed from Earth) even at it's best. And, it will also be quite low (comparatively) in the sky. During this apparition, the maximum altitude Mars will attain in the sky will be about 30 degrees -- that's pretty low and we downunder will all be looking through a lot of air (and consequently moving air) while observing Mars this time.
The combined effect of both these factors means any advantage the 16" might have over and 8" in pure theoretical resolving power, is likely to be much diminished unless the seeing is almost perfect -- rare if not very, very rare in Summer and that low down to the horizon. Sorry to say, but that is the truth _as I see it_. The next reasonably good apparition of Mars as seen from downunder is about 6-8 years away I'm afraid. It won't be impossible to see great detail this time -- just a lot harder and rarer than in say 2003 or 2005.
In summary, this time around, the 16" won't be a big (if any) advantage _on Mars_ over the 8". However, on Jupiter and Saturn next year which are both somewhat if not much higher in the sky, it would be somewhat better than the 8" -- and a lot brighter image.
And then of course there is the vast leap (no, not tempted to say "quantum leap") in performance on deep-sky stuff. A 16" has 4-times the light-gathering power of the 8" meaning everything deep-sky will be 4 times brighter and much, much better resolved. The difference between say 47 Tucanae (NGC 104) in an 8" and a 16" has to be seen to be believed!
The switch to a _truss-tube_ Newtonian over commercial Schmidt Cassegrainian also means you will have to learn to collimate the telescope well (every time you assemble it) to get a really good image (it's not that hard!) and be prepared to do a bit of maintenance from time to time in giving the mirrors a wash to remove dust etc.
I've had experience with two different 16" lightbridges and for the money, they are very nice 'scopes -- not perfect in every way but really very good for the price.
That's my two-bob's worth!
What do others reckon?
Best,
Les D
Contributing Editor
AS&T
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