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Old 15-06-2011, 12:59 PM
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First obs with 8" dob, 14/6/11

Finally, I got around to giving my 8" dob which I purhased from fellow IIS member Wren a while back, a quick obs session. The OTA was hand made by Astronomy Alive in Melbourne and features premium optics along with a fully flocked tube. Not sure who made the optics, but a couple of third party reports I heard of spoke highly of this scope. The scope is actually cleverly designed, both the secondary and primary mirrors are generously recessed into the tube to prevent them dewing over, and I found that after two hours in the heavy dew, both mirrors were bone dry.

The seeing was pretty poor once again, and dew was very heavy. I have made some mental comparisons to the 12" SDM, which I had out the previous night in essentially identical seeing conditions.

Only observed Saturn and the moon. After an hour or so of cooldown, Saturn was nice and crisp using the 8mm EP at 150x, and I'd say displayed slightly better contrast than with the 12" with the same EP (167x, keep in mind that the 12" mirror is due for a recoat ), conversely on this scope both mirrors are virtually pristine. The same focal length EPs yield similar magnification in both this 8" and the 12", as there is only about 130mm difference in focal length between the two. However, the Cassini Division was noticably harder to see than in the 12", but that is to be expected with the reduction in aperture.

At moments of ok seeing, using the 5mm EP at 240x was barely possible , with Saturn at times rendered fairly crisp with the Cassini Division more obvious and a nice hard edge to the globe and rings.

Now, the moon.
Seeing was blurring the contrasty areas between sunlit and shaded areas quite severely, but at 150x the view was indeed contrasty and pleasant with nice inky black shadows. Again, I suspect a slight increase in contrast over the 12". Looking at features along the terminator it was fascintating seeing mountain peaks cast jagged, triangular shadows off into the distance. In steadier moments, detail in the highlands and cratered areas was rich and crisp at 240x. If it had been a steady night, the view would've been amazing. You could just tell.

The four main craterlets in Plato (A, B, C, D) were plainly visible at 150x, but G and H only just barely, due to the seeing rather than anything else. At 240x, the big four were seen as pits intermittently, and G and H were just visible. The previous night with the 12" at 267x, the big four were distinct pits, G and H were quite straightforward to spot and also another two, E and F, were spotted without difficulty. (see attached image for David Knisley's Craterlets guide).

With these initial observations, this scope has left a sweet taste in my mouth Only gripe is the mount, not sure who made it, but for high magnification work it does wobble a bit when you focus, however for lower power it's quite adequate. I found myself missing the feathertouch and rock solid mechanics of the SDM!

The sexy black Sonotube is quite lightweight, and coupled with what I think is going to be a great set of optics, this scope will make an excellent grab n go of sorts, for planetary/lunar viewing or shorter sessions when hauling out and assembling / dismantling the 12" is too much work.

Eventually I plan to replace the mount, probably put on a 2-speed focuser and while we're at maybe some dew heaters etc. Hmmm wonder if SDM do the odd pimp-my-scope job on the side? That would make a sweet as planet killer!


couple of pics of the beast....
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  #2  
Old 15-06-2011, 04:04 PM
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Paddy (Patrick)
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Sounds a lovely acquisition Sab.
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Old 15-06-2011, 04:46 PM
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DavidU (Dave)
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Nice one Sab. It probably has Parks optics in it. Is it an f/6?
Also, my mate who bought the 10" from you loves it..Thanks
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Old 15-06-2011, 05:48 PM
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Quote:
Originally Posted by DavidU View Post
Nice one Sab. It probably has Parks optics in it. Is it an f/6?
Also, my mate who bought the 10" from you loves it..Thanks
Great news about your mate. Glad he enjoys the scope

Yeah the scope is an F/6. Hanging out for some decent seeing one of these days to really see what it's capable of.
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Old 16-06-2011, 11:31 AM
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barx1963 (Malcolm)
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Nice going Sab. Just on question, do you have enough scopes? I count 4 in the picture plus the SDM makes 5. My SWMBO complains about me having 2!
The mount looks a little like the ones Orions Optics in the UK do for their dobs.

Malcolm
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Old 16-06-2011, 12:00 PM
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Quote:
Originally Posted by barx1963 View Post
Nice going Sab. Just on question, do you have enough scopes? I count 4 in the picture plus the SDM makes 5. My SWMBO complains about me having 2!
The mount looks a little like the ones Orions Optics in the UK do for their dobs.

Malcolm
lol too many scopes mate! Trying to trim the collection so I end up with the SDM for deepsky stuff, the 8 inch for solar system and quicker sessions which don't justify 15 return trips to and fro the backyard, the 120ST for widefield and 4.5" newt which I'll keep for quick look planetary, it's actually very nice in that regard IMO I remember getting lovely crisp views of the moon with it at 200x. The mount on that is broken and probably won't get more than 50 bucks for the OTA so it'll just share that ALt Az mount with the 120ST.

The mount I'm going to replace sometime, it's just too shaky at high power. Smooth motions though.

Last edited by pgc hunter; 16-06-2011 at 02:43 PM.
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