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5" Refractor or 8" Newtonian for Lunar/Planetary Observing

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#26 Rick Woods

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Posted 03 October 2015 - 04:57 PM

I would take a high-quality 8" f/6 on a GEM over a 5" refractor. The GEM will negate all the disadvantages of the Dob.

My old Meade 826 easily gives me a sharp, detailed Mars at 400x (conditions willing). I wouldn't trade it for any 5" scope ever made.

#27 Markab


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Posted 22 October 2015 - 07:43 AM

I may be too late to add my .02, but it should be valuable.


I have owned a AP130EDF and the GT model. I now own an 8" f/5.5 Portaball.


My conclusion: The Portaball rips the APs to shreds. A perfect 8" mirror over a perfect 5" lens...no comparison, obviously assuming collimation and thermal equilibrium. Especially since the Portaballs are constructed with fans and other ergonomics to help with the thermal adjustment.  And I'm solely talking about visual planetary, since that is almost exclusively what I do.

#28 Starman81



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Posted 22 October 2015 - 03:06 PM

Some thoughts on the topic...


I had my best view ever of Saturn through my modest SW 120ED refractor earlier this year. I've also had a best ever view of Jupiter this year with 8" dob with Zambuto primary. In both cases, each scope was the only one set up that night and rare excellent seeing conditions on both nights. I don't think that there would be any regrets with either of your choices, optically speaking. 


Easy setup? That is probably going to go out the window since you will want tracking--this is high-power lunar/planetary after all. That means a GEM for the refractor or an EQ platform for the dob...


Quick cool down? A 1"-thick quartz mirror with a fan blowing on it is probably not too far behind a 5" triplet but I could be wrong here. 

#29 Scott99


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Posted 22 October 2015 - 05:42 PM

I love apos but Portaballs are legendary planetary instruments too!   CO is only 20%.  Unless seeing is bad the 8-inch should win.   I know you guys have much better seeing in Central coast CA that around here.    Seeing around here is usually poor and it's cold at night, apos rule in those conditions.  But you guys have the laminar flow off the ocean.


I second the motion for a Teeter solid-tube Newt.  I've got an AP160 refractor and I'm tempted to try a Teeter STS 10-inch.  The tube weight is about the same as the 160, although much wider in diameter. 


I'm thinking it'd be fun to mount the Newt on my equatorial.  I guess I'd need rotating rings and a lower tripod.  But a premium 10-inch Newt on a real equatorial mount would be cool! 


another thought - if planetary views are what you're after why not try an older AP 130 f/8. You'll need a barlow with the f/6 to get high power.  Or maybe even a TEC140.  The 130 f/6 would have the advantage of transporting and setting up quickly - the OTA is only 15 pounds.  The small size and weight allow you to use it on alt-az mounts too.   That would be the absolute fastest way to get viewing - no collimation or fans, just attach to a DM6 or something similar.


The scope I use the most is an 120mm Star 12 ED on a Tak Teegul.  It's ready to go fast and always gives a very sharp image.  You know whether seeing is bad or not right away, you're never wondering about collimation or cooling.   Many of us sacrifice aperture to get the razor-sharp views and contrast that only an unobstructed apo can provide.

#30 GeneT


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Posted 24 October 2015 - 02:48 PM

I have thought a lot about your telescope scenario, but with one difference. A 5 inch refractor to go along with my 12.5 inch Portaball. The Portaball is a well designed, very portable instrument. A question like the one you posted brings me to the thought that sometimes we need to have more than one telescope in our stable. 

#31 azure1961p


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Posted 26 October 2015 - 08:13 PM

I ve   had the 8" side by side on two occasions anyway with a 5" apo one being an AP and the view wasn't bad but it was kind of a shrug.  I don't recall the other brand -  it was dark after all.  Both times the view was Saturn.  It was nice  but again I kind of shrugged and moved on.  A ten inch F7 newt -  now that was memorable.  The five inch views never left me envious.  They were nice but by comparison there was no want-factor.   The ten though... Yeah iIwanted those views through my 8!



Edited by azure1961p, 26 October 2015 - 08:15 PM.

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