10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

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Refractordude
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10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#1

Post by Refractordude »


Which of these will show brighter DSO? Left click the image.
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Graeme1858 Great Britain
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#2

Post by Graeme1858 »


Refractordude wrote: Tue May 18, 2021 4:39 am Which of these will show brighter DSO? Left click the image.

Dunno! But the chart is very interesting, cheers.

Regards

Graeme
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#3

Post by Richard »


Interesting I cant see Pleiades any more so my sky must have deteriorated to a 10 now :shock:
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#4

Post by helicon »


As you go up on the scale towards Bortle 1 deep sky objects become increasingly visible. I am in a Bortle 7 zone. (Used to be in 6 but a new streetlight dropped the skies to Bortle 7).
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#5

Post by Bigzmey »


Aperture is a queen, but dark skies is the king! I would take 6" refractor at Bortle 2 over 10" DOB at Bortle 4 any time.

Bortle 2 is not accessible from my home by any practical means, but from my experience 4" refractor at Bortle 4 has about the same reach as 8" SCT at Bortle 6.
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#6

Post by pakarinen »


By those criteria, home is a 7 and my usual dark sites are 4. Seems about right. Thankfully the sky isn't orange here. Yet.
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#7

Post by kt4hx »


Here is a link to the image you posted, it will be easier for folks to read: http://www.bigskyastroclub.org/lp_bortle.html

Anyway, I would take some of the chart with some grains of salt. First of all, the colored scale has nothing to do with the Bortle scale. The colors are extracted from the light pollution maps created from nighttime satellite imagery with an algorithm applied to "estimate" the spread of sky glow over terrain. Any correlation between the two are coincidental and not wholly reliable. Also, NELM is very individual. You could place 10 people next to one another and ask them to estimate the dimmest star they can see at the zenith with averted vision. While you might not get ten different answers, you certainly would not come to a real consensus. Variations of optical acuity and experience have a major impact here. Also because of those differences people will see things differently under each of the columns. All that doesn't mean that the scale in ineffective, only that it is not a perfect scale for sky assessment. It is a tool, just not the final answer. Spending time under you sky will give you the best understanding of what you are dealing with. The Bortle scale is a moving target, meant to estimate one's conditions in the moment based on a set of criteria and can vary night to night and sometimes hour to hour. The colored maps are static and do not reveal that kind of variation, though they too can be a good tool for general assessment.

Now, as to your actual question, as others have said, the scale runs from 1 (darkest) to 9 (brightest) skies. As Andrey stated, aperture is a queen and dark skies are the king. I always call dark skies the great equalizer. My home skies used to be a solid Bortle 5, but that has deteriorated to more of a Bortle 6 and I can most definitely tell the difference. Our dark site house is typically Bortle 3, but can be as good as a 2 from time to time. That is why I keep my 17.5 inch at the dark site house full time, and the 10 and 12 inch dobs at home. While I could certainly keep the larger one at home, and it would reach deeper there than the smaller apertures, I prefer to have the most aperture at the darker site so I get the best of both worlds - aperture and dark skies. :)
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#8

Post by StarBru »


Here where I live in Casa Grande, Arizona, I have the Phoenix area glow in my Northern sky, and Casa Grande glow in the Southern sky.
Looking North, I typically cannot see the fainter stars in the Little Dipper, so Bortle 7 or 8. I can never see M31. In the Southern sky, I have no problem seeing the Orion Nebula's glow or the Pleiades overhead with some of the MW above on good nights but not near the horizon. I would say Bortle 6 usually before midnight with Bortle 5 on good nights or after midnight. I do all my observing in the backyard and very rarely go to a darker sight.
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#9

Post by pakarinen »


StarBru wrote: Thu May 27, 2021 4:49 pm I would say Bortle 6 usually before midnight with Bortle 5 on good nights or after midnight.
Yeah, that's why I prefer observing before dawn. Not gonna happen now with twilight starting between 0300 and 0330 here though.
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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#10

Post by WilliamPaolini »


I lived in a Bortle 4/5 sky for the past 3-4 years, and I have both a 10" Dob and a 6" Apo. It largely depends on the objects I am viewing as to which I will use. For the most part, I prefer the 6" refractor because even at f/8 it provides wider views so larger objects can be framed nicely, it is thermally more stable than the Dob so star points are more pinpoint and aesthetically pleasing, and it has no issue pumping magnification. Overall I feel it is both a more flexible instrument as well as having a more refined visual presentation. So if open clusters or globular clusters or showcase nebula or double stars or planets are on the target list then the 6" refractor typically provides the more pleasing presentation for me. However, if my primary focus for the evening are galaxies or planetary nebula or dimmer lackluster clusters that need aperture to bring them out best, then the 10" Dob gets used. When I was at higher altitude Bortle 1/2 and 2/3 sites and had access to numerous instruments of many aperture classes, I tended to prefer the smaller aperture instruments over the larger ones as the views were superb even in the small scopes and of course being smaller and easier to manage made it so my focus could stay more on the skies rather than the equipment. I have 10", 8" 6", 4" and 3" scopes. If I had regular access to darker sites I think I would only use the 8" f/5 Dob and the 4" Apo and those two would satisfy me no matter what the skies were. An 8" has a lot of reach and an f/5 can still get a reasonably large TFOV so is quite flexible. It is small also so easy to manage. Given what I experience across all my refractors in 3, 4, and 6", I think if I could only have one I would probably opt for a 100-120mm Apo.

For me, I do not view it as using differing apertures based on sky conditions or locations. I prefer to use the aperture classes I like using best and then just adjust my object lists so they suit the capabilities of the skies. So for me I treat apertures as more or less a fixed thing because operating a scope is more then just about its aperture. I've got to feel comfortable with its operation overall and want to keep the hassle-factor down so the equipment gets out of the way and I can just focus on navigating the skies. In that respect a 100-120mm refractor and an 8" Newtonian I feel are friendliest overall and both with plenty good capability. If there was not a Dob in the mix then I would probably bump the aperture of the refactor up to 130mm as any larger than that and they become little beasts.
-Bill

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Re: 10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

#11

Post by Ylem »


At a Bortle 6/7 here, I pretty much have to use the C8 to pull anything out. I had a 10" Dob many years ago and sometimes miss it.

That said, my ST80 and 127 Mak do get used the most because of the easy set up.
If I do travel to my club's dark site, it's worth bringing the C8, and have considered getting a 12" Dob for those nights :)
Clear Skies,
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