davinci..
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Reged: 01/29/07
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Is a big dob worth it, in light polluted skies?
#2430300 - 05/30/08 09:22 PM
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Ive been saving every penny I can(and i mean every penny), and am ready to purchase a good scope. I started off small with a 4.5in skywatcher, to learn the hobby, and now after a year and a half its time to move up. However I live in a fairly large city, and light pollution is obviously pretty bad.
Im struggling with the choice between getting the next "good" step up, an 8 inch dob, or going all out, and getting a 12 inch dob. My concern is whether or not the 12 inch is worth it, givin my light pollution situation. Now obviously a 12 inch would let me see more, as it will collect more light, but wont it also collect more "unwanted" light? Could light pollution essentially "cap" how much I can see? or hamper how much more I could see over an 8 inch? Would it be worth over double the cost of the 8 inch?
For reference regarding my light pollution.
My little 4.5in f4.4 sky watcher on a "really good clear night" seems to cap out at about magnitude 10.30 for point light sources(ie, i can see Rhea, on most nights though just titan), and other 10.25-10.30 mag stars seems to be my limit. However i cannot for the life of me even glimpes m101 at mag 7.9. Though the ring nebula in vega is detected easily. Strange as it is.
Also for reference my scope choices.
8" Sky watcher dob, likely a r&p focuser, and a straigh through finder. $389 with tax $440.
or
12" skywatcher collapsible.
2 speed crayford, and right angle finder, and the ability to collapse down to about meter(3.3 feet) which should fit in the back of a car nicely. cost $949, $1072 after tax.
Either one would likely be my scope from here on out.
thoughts?
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phanfave
Carpal Tunnel
Reged: 08/21/06
Loc: Pioneer Valley
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Re: Is a big dob worth it, in light polluted skies
[Re: davinci..]
#2430323 - 05/30/08 09:33 PM
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12" will show you more and deal with the light pollution better than the 8" scope hands down. Now the question is can you use this scope at home or do you have to travel to use it? I ask because the 8" scope will be much easier to travel with, even if the 12" is a truss scope. I'd go for the 12" unless you really don't want to lug a scope of that size around. For me living on the second floor, 12" was too much but 10" is my sweet spot. When I move I hope to get a 15-18" scope.
Sean
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tlogan6680
super member
Reged: 01/31/05
Loc: Monterey, CA
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Re: Is a big dob worth it, in light polluted skies
[Re: phanfave]
#2430358 - 05/30/08 09:47 PM
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I have a 10in dob (f6) and live in a town with a neighbor with bright nite lights. I have strung some cords and place sheets on them when i view to cut down on the light. Yet, monday nite i saw structure in M51 (spirals faint but there). So you CAN see faint fuzzies with a little prep.
I do not have to move my dob, it is on the porch, so wieght is not a problem. If you have to move it then get an 8in. If you are not real familiar with star-hopping, then look at Orion's Inteliscopes.
Tom in cloudy CA
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Bill Jensen
sage
Reged: 10/23/04
Loc: Springfield VA
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Re: Is a big dob worth it, in light polluted skies
[Re: tlogan6680]
#2430449 - 05/30/08 10:32 PM
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One way to check this is to ask fellow club members in your area if they have 12 inch scopes for use at their homes, and what they observe. I live in the light polluted DC area, and find that most of my home viewing is limited to planets, open clusters, and double stars. Even if I detect a DSO, the view just is not that good unless it is one of the brighter DSOs. I have owned 12 and 10 inch scopes, and will be getting a 16 inch dob this summer for use away from home.
My most used scopes are my small TV refractor, and my 8 inch truss tube dob. The 8 is a good size for planetary viewing without having a significant lugging factor, which, in my townhouse, is an important consideration.
If you keep your 4 inch scope for quick, frequent views of brighter objects, and have a 10- 12 inch dob for deep sky observing, and traveling to your club's dark sky sites, that may make for a great combo.
If your club has loaner scopes available, it may make sense to try a larger scope out for a few weeks and determine what you will think that you will use the most.
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Deep13
Carpal Tunnel
Reged: 01/25/05
Loc: NE Ohio
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Re: Is a big dob worth it, in light polluted skies
[Re: Bill Jensen]
#2430603 - 05/30/08 11:48 PM
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It is if you can easily move it when you want to get away from the lights. If a 12" will be stuck at home while an 8" could be driven to the sticks, then go smaller. Get the biggest one you can lift and fit in the car.
NB: Blocking glare as previously described and use of a sky glow filter helps a lot.
Edited by Deep13 (05/30/08 11:50 PM)
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EclipsingBinary
super member
Reged: 03/12/08
Loc: The Motor City
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Re: Is a big dob worth it, in light polluted skies
[Re: Deep13]
#2430637 - 05/31/08 12:15 AM
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I think you'd like a 10" or 12"
I liked the difference I noticed even in light polluted skies between an orion 8 and a 10 so I bought the 10. The 12 was nice and I noticed a difference between that and the 10 but to me it was'nt as big as the difference between the 8 and 10, plus the 12 was a little large for my minivan when I wanted to go to a dark site, even when the tube was separated from the base. If you have the means to deal with the larger aperture scopes, even though the one you are thinking of collapses, then go for it. I do 90% of my viewing from a park about 1000' from my house, so I put some wheelbarrow handles on my 10 and it is so easy now to get that thing over there and start viewing. Now I'm going to go larger at some point.
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sixela
Postmaster
Reged: 12/23/04
Loc: Boechout, Belgium
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Re: Is a big dob worth it, in light polluted skies
[Re: davinci..]
#2430847 - 05/31/08 04:24 AM
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Now obviously a 12 inch would let me see more, as it will collect more light, but wont it also collect more "unwanted" light?
Yes. But at equal exit pupil with a small scope (i.e. more magnification in the large scope), the sky background will appear just as light or dark, but on most objects the larger apparent size of details in the larger scope (because of the larger magnification) will make them more visible there.
That doesn't apply to very large objects like M31 - if you want to see all of it, in light polluted environments a scope that fits it all into view at 2mm magnification may actually give you the "best" view. But in my experience, it won't be very good.
Quote:
Could light pollution essentially "cap" how much I can see?
Yes. Light pollution decreases the difference between an 8" and a 12" (if scopes could overcome light pollution with a large enough scope we should be able to observe during the day), and for all contrast details of extended objects there is an amount of light pollution that will essentially render it invisible in any scope.
Note that for stars the picture isn't quite as bleak, because these *do* become brighter in large scopes. Large clusters are again another matter - in a large scope you may want to magnify so much to make the background dark enough to be pleasing that the cluster no longer fits in the view.
In other words: large scopes frequently don't make good very wide field scopes in light polluted environments.
Quote:
or hamper how much more I could see over an 8 inch? Would it be worth over double the cost of the 8 inch?
Perhaps, perhaps not - that's a hard judgement call. One thing is sure, though: if you can't transport the larger scope to a dark site once in a while but you can do so for the smaller scope, then go for the smaller scope. Never buy something too big to be moved to a dark site.
Quote:
However i cannot for the life of me even glimpes m101 at mag 7.9.
That's because it's a low surface brightness object - it's harder than the integrated magnitude would make you think because the light is spread over a large area. M33 is another difficult target in light polluted environments for the same reason, while it's an easy naked eye object on very good nights at a dark site.
M101 is even difficult at our darkish Mag 5.7-6 site: even on good nights and in a 16", the difference in appearance between views low over the horizon and views close to zenith is very striking. Even within the one night, M101 can turn from a barely discernible vague glow with a slightly clearer central core into a galaxy with four clearly delineated arms in which you can see a fair number of HII-regions, an object that can rival M51 in beauty.
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InkDark
Carpal Tunnel
Reged: 10/29/07
Loc: Lanaudiere, Quebec, Canada
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Re: Is a big dob worth it, in light polluted skies
[Re: sixela]
#2431165 - 05/31/08 10:28 AM
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You got great advice, so I won't add anything else but this; If you get 12 inch collapsible SW, don't forget to give us your thoughts and a first light report.
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ken scharf
sage
Reged: 02/09/08
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Re: Is a big dob worth it, in light polluted skies
[Re: InkDark]
#2431279 - 05/31/08 11:36 AM
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The astronomy club I belong to has an observatory at the edge of town. Still under light polluted skies, but at least the nearest street lights are a mile away. They have several scopes including an old Coulter 13.1" dob (close to the 12" size you are considering). With the base mounted on casters the thing rolls out of the building easy enough (though it takes two to lift it). Very nice views though something this size, the Orion Nebula shows structure. How much better it would look with better optics, but the club uses this scope for the same mission that John Dobson would.
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panhard
It's All Good
Reged: 01/20/08
Loc: Markham Ontario Canada
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Re: Is a big dob worth it, in light polluted skies
[Re: ken scharf]
#2431395 - 05/31/08 12:47 PM
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Davinci
If you have to travel to view at all I would limit my size to 10". It is still portable with a little effort, gives great views,will fit in backseat of my pickup,and does not cost too much. Collimation is more critical though. 
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davinci..
member
Reged: 01/29/07
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Re: Is a big dob worth it, in light polluted skies
[Re: Deep13]
#2431425 - 05/31/08 01:00 PM
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It is if you can easily move it when you want to get away from the lights. If a 12" will be stuck at home while an 8" could be driven to the sticks, then go smaller. Get the biggest one you can lift and fit in the car.
NB: Blocking glare as previously described and use of a sky glow filter helps a lot.
As it turns out, the 12" collapsible should turn out to be the same to transport as the 8", though heavier. An 8" or 10" for that matter would lay accross the backseat in most cars. The 12" collapsed, could easily do the same.
example
So i cant help but think they will be the same in terms of transportability.
more info here: Sky Watcher
And the reason for going up to 12" instead of say 10", is because the collapsible 8 and 10s are quite a bit more expensive then thier standard counterparts, where as the 12" is the same price for either. Which just seems like the best possible deal. 8" standard? or 12" collapsible? just dont know what to do.
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InkDark
Carpal Tunnel
Reged: 10/29/07
Loc: Lanaudiere, Quebec, Canada
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Re: Is a big dob worth it, in light polluted skies
[Re: davinci..]
#2431490 - 05/31/08 01:33 PM
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I'm afraid not, the 12" collapsible will be much fatter and heavier than the solid 8 inch. You can see my comments in this threads - Thread on new SW flextube . OOH, the 12" collapsible will in fact be shorter. I was thinking about the 12 inch as a next scope but when I saw it I thought...man that thing is still pretty big. Moreover, when I saw how small is the 10 inch collapsible and how it would be easy to transport,... 
Another thing have you thought about the Lightbridge?
Because I think that it's not out of topic here I will ask this next question: How much "harder" is it to collimate an F/4.7 compare to an F/5?
Thanks
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InkDark
Carpal Tunnel
Reged: 10/29/07
Loc: Lanaudiere, Quebec, Canada
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Re: Is a big dob worth it, in light polluted skies
[Re: InkDark]
#2431499 - 05/31/08 01:38 PM
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As usual Alexis has great advices. But if you have light polluted skies the best advice he gave you IMO is this:
Quote:
Perhaps, perhaps not - that's a hard judgement call. One thing is sure, though: if you can't transport the larger scope to a dark site once in a while but you can do so for the smaller scope, then go for the smaller scope. Never buy something too big to be moved to a dark site.
Clear and dark skies!
Edited by InkDark (05/31/08 01:39 PM)
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Achernar
Postmaster
Reged: 02/25/06
Loc: Mobile, Alabama, USA
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Re: Is a big dob worth it, in light polluted skies
[Re: sixela]
#2431624 - 05/31/08 02:51 PM
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Perhaps, perhaps not - that's a hard judgement call. One thing is sure, though: if you can't transport the larger scope to a dark site once in a while but you can do so for the smaller scope, then go for the smaller scope. Never buy something too big to be moved to a dark site.
That is excellent advice. If a telescope is too large or heavy to take to a dark site at least occasionally, it's a poor choice. That is why I am glad I got the 10-inch Dob I have now instead of a solid tube 12-inch. There's no way I could put one of those in my car. I take the 10-inch to dark sites all the time. Big apertures are indeed worth it in light polluted areas, as long as one can transport it to
a dark site too.
Taras
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Jan cz
member
Reged: 09/02/07
Loc: Czech Republic, Jistebnik
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Re: Is a big dob worth it, in light polluted skies
[Re: Achernar]
#2432070 - 05/31/08 07:15 PM
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I live in a village 10 km from 1/2 million industrial city. Nearest street light is 40 meters away.
In ETX-90:
M57 is small circular blob with a hint of darker inner area
M101 not visible
M51 not visible
In 12" Lightbridge:
M57 is a bright ring with wide dark area inside
M101 on threshold of visibility on good nights
M51 spiral arms visible using adverted vision
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LateViewer
Pooh-Bah
Reged: 11/17/05
Loc: Manhattan
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Re: Is a big dob worth it, in light polluted skies
[Re: Jan cz]
#2432185 - 05/31/08 08:23 PM
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Bigger is better. Even when the sky is not so good.
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sailor70623
Post Laureate
Reged: 01/12/08
Loc: Ok.
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Re: Is a big dob worth it, in light polluted skies
[Re: LateViewer]
#2432339 - 05/31/08 09:58 PM
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I find that bigger is better in light polluted skies. Why you ask. Simple, LPR filters can only reduce the light coming through the scope, a narrow band filter is too dark for use on scopes under 8". A broad band LPR filter is too dark on most 5" scopes. BUT a narrow band filter on a 12" while it won't get rid of all the light pollution, will give better views than when used on a 10" scope. You will need a shroud if you are thinking something like a Mead Light Bridge, but with a narrow band filter you will be able to get better views with a larger scope. A truss Dob is always transportable to darker areas too. Even in a little car.
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bartine
Pooh-Bah
Reged: 10/03/07
Loc: Potomac, MD
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Re: Is a big dob worth it, in light polluted skies
[Re: sailor70623]
#2432379 - 05/31/08 10:22 PM
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I live 30 miles North of downtown Atlanta in a neighborhood with street lights (and porch lights).
I have a Discovery 15" solid tube, a Mead 826 and had a C102 (by Vixen).
Doubles, planets and star clusters are OK. Faint fuzzies? They are faint no matter what scope you look at them through.
I honestly got far better views through my ancient 8" Orion "star hopper" at a dark sky site than I have ever gotten through several 12" or bigger scopes from my yard in suburbia.
Now - with that 15" Discovery, you can see more stars in the Trapezium, more moons of Saturn, Jupiter, ect.
But - I say - get the best smaller scope you can afford (optics really matter) that is easy to transport, and take it on the road once a month.
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Markovich
professor emeritus
Reged: 05/22/07
Loc: Central Ohio
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Re: Is a big dob worth it, in light polluted skies
[Re: bartine]
#2433022 - 06/01/08 10:20 AM
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Just my 2 cents, I bought an Obsession 15 and 2 years later we had twins! So, obviously, my dark sky observing has kinda stopped for a few years. I live in a suburb of Columbus, Ohio and routinely get my 15 and other scopes out ( just to get starlight into them). Not once has the 15 been outclassed by the smaller scopes on any object, regardless of seeing conditions. I'm not a believer that smaller scopes do better under poor conditions. Aperture( and good optics) always rules:)
Mark
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Jarad
Postmaster
Reged: 04/28/03
Loc: Atlanta, GA
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Re: Is a big dob worth it, in light polluted skies
[Re: Markovich]
#2433053 - 06/01/08 10:47 AM
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There are 2 issues here:
#1 - Viewing from a dark sky site is better than from light pollution.
#2 - Viewing through a larger scope is better than viewing through a smaller scope, regardless of the skies.
So, I would say get the largest scope that you are still able to transport to a dark site. I agree that if the size of the scope makes it too difficult to take to a dark site, you are better off with a smaller one. I also agree that a larger scope will outperform a smaller one even in light pollution. In this case, I think the 12.5" (especially if it's a truss) would be the better choice - it should still be portable enough to take to dark skies when you have the time to go. If for some reason you don't think you will be able to transport the 12.5", then size down to something you can.
Jarad
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