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MTA61
journeyman
Reged: 02/28/06
Posts: 8
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I am getting rid of my Celestron C4-R I bought on ebay about a year ago as I just can't take the shaky mount and lousy focuser any more!I've tweeked the focuser and changed the grease and it's still terrible. I don't want to spend any money upgrading it either.
I had an old Coulter Optical 8" Dob back in the mid 80's and remember how much easier it was to set up and just enjoy viewing! I could sit in a chair most of the time and never had to get down almost on my belly to view objects overhead.I should never have sold it!
My question is; I have decided on getting a Zhumell Dob but can't decide between the 8" or 10". I know the 10" is going to give brighter views, but won't the 8" at f5.9 give a lttle bit sharper views? My daughter likes to view the moon and planets with me. She's not as into the fainter stuff as I am. Has anyone owned both an 8" and 10" Dob who can give me a comparison between the two? I guess I'd like to know if there is a discernable difference in contrast between the two scopes different focal lengths?
I am also concerned about portability. The weight is not a problem, but fitting it my Hyundai Elantra may be. It has a fold down back seet so I think even the 10" should fit. Does anyone transport one in a car with foldown back seat?
Thanks for any help you can provide!
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Luigi
Postmaster
Reged: 07/03/07
Posts: 5272
Loc: MA
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Both have nearly the same focal length. The 10" simply adds more aperture, and with it, a bit more coma. On axis views should be a very slightly sharper and appear a little brigther in the 10", other things being equal. The biggest reason to get the 10" is to avoid regretting not having gone for it if you get the 8.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Darren Drake
Pooh-Bah
Reged: 10/09/02
Posts: 1457
Loc: Illinois
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The 10 inch views aren't just a little brighter they are 56% brighter which is significant. It's also not that much longer just fatter. It will definately show more on deep sky and a little more on lunar planetary given favorable conditions so I would recommend the 10.
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Astronomy educator/Sidewalk astronomer
Owner of Astronomy Delight franchise
18 inch f4.42 Dob on eq platform w ST120 f/5 finder
12 inch Zhumell Dob modified by Brian Reed on eq platform
8 inch f/8 eq planetkiller
William Optics red 10th Anniversary 80mm FD
PST
24lb eyepiece box
Cernan Space Center astronomer
Member of Northwest Suburban Astronomers
Edited by Darren Drake (11/17/09 07:51 PM)
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cdndob
professor emeritus
Reged: 07/28/06
Posts: 710
Loc: The Great White North
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I have 6, 8, 10 and 12 inch reflectors and I find the views get better, planets and DSOs, each time I go up in size.
Probably the best balance of views and portability is a 10 inch being the best views that still fit across the backseat of almost any car.
Steve
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BSeward
professor emeritus
Reged: 09/19/06
Posts: 723
Loc: 15 miles north of Snow Plop.
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Got a Z8. Love it! GREAT telescope!!
That being said,
Shoulda bought a Z10.....
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Z8 (Freshly Flocked - thanks Steve!))
Telrad with Romisen L-B030 GLP attached to finder mount
1.8X Barlow and a bunch of inexpensive eyepieces.
Bob's Knobs! (Thanks, Bob!)
The "B" stands for Bill, (and, sorry to say, Bald!)
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PJ Anway
Pooh-Bah
Reged: 06/04/03
Posts: 1295
Loc: Michigan's U.P.
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The views through an 8" and 10" are not all that different. The 10" will have 1-1/2 times the light grasp of the 8" and you really need about 2 times ( a 12" ) before the difference is striking. The 8" will have some advantages - smaller size/portability, less weight, shorter cool-down time, less coma, etc. that may outweigh the small gain in resolution and limiting magnitude. Only you can weigh the factors and decide which is best for your situation.
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Clear Skies,
PJ
Lookum Observatory
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MTA61
journeyman
Reged: 02/28/06
Posts: 8
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Thanks for everyones help so far. It looks like the most votes go to the 10" for more aperture and no regrets for not getting the larger scope.
PJ, you bring up some good points about the 8" though. I would like to bring the new scope up to my brothers house which is a few hours away, so with my wife and daughter in the car the 8" might be a better fit. We usually stay over so we pack some clothes and stuff too.The refractor was never a problem to transport up there.
Also PJ brings up the point of less coma. It's been many years since I've looked through my 8" Coulter, but I do remember at f4.5, it had a bit of coma at the edge of the field of view. Is the coma much different between the two scopes for people who have looked through both? Also I do have some cheaper Celestron eyepieces where the longer focal length 8" might be better.
Decisions, decisions!
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12951
Loc: Rockford Illinois
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The only thing larger (Bulk) between them is the base and the tube diameter... The tube length is about the same (within inches). So you're looking at taking up the same space in the car with either scope.
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Neo... (Jeff)
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10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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lymorkiew45
scholastic sledgehammer
Reged: 12/30/07
Posts: 894
Loc: Surfing the galaxy...
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Why upgrade to a 10", when an 8" will give you virtually the same views, I would go for portability in my opinion. If you want a real improvement, you need to double the light gathering power, and even though a 10" gathers around 56% more light then the 8", this is hardly impressive at all, and everyone's opinions will differ, because the eye works logarythmically, the gain in brightness would be like 5-10%, not 56%, however I think the 10" is the goldilocks of the large apertures, but if portability is more your speed, I would get the 8", and as a result you won't be losing much over the 10", but the 10" might give you a marginally slight improvement in resolution, but it will be subtle...clear skies... 
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saxmaneagle
sage
Reged: 08/21/07
Posts: 244
Loc: Saint Francis, MN
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Repeat after me..."Bigger is better...bigger is better!"
As far as coma goes, get a TeleVue Paracorr. They are an expense, but when I plopped one into my F 4.5 scope, the 'warp drive effect' disappeared, and hello flat pinpoint views edge to edge. Well worth the money. Many people don't think that coma (warp drive effect when moving the scope - plus seagull shaped stars at the view edges) is that big of a deal - but I've found once I started using the parabolic corrector, I almost never have it out of my focuser. Just my humble 2 cents. You also gain 15% magnification with it.
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Meade 16" Lightbridge
TV Paracorr
Howie 2" laser & BLUG
Many Many EP's
Dual axis Round Table Platform
20x80 standard Oberwerk binoculars
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"Inside us all are such Wonders. Search yourself, find them...share them...and Dream, of a better tomorrow"
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