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Observing >> Deep Sky Observing

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Mta472
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Reged: 02/28/06

Loc: CT
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5677133 - 02/13/13 07:35 AM

If you do not live in a dark zone, IMHO you would be throwing money away on a 16 inch vs a 12 inch because of light pollution. I live in CT and went from an 8 to 12 inch and it did NOT make much difference.

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Starman81
Carpal Tunnel
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Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: 12" versus 16" for galaxy structure new [Re: Mta472]
      #5678078 - 02/13/13 05:49 PM

Quote:

If you do not live in a dark zone, IMHO you would be throwing money away on a 16 inch vs a 12 inch because of light pollution. I live in CT and went from an 8 to 12 inch and it did NOT make much difference.




Really? I would like to hear more about that since I do plan on going to 12" of aperture at some point...

Also, what's with people with big dobs always having smaller cars? It is a trend that I've noticed. It's like the challenge of hauling around a big dob wasn't enough so you want to try to do it with smaller and smaller cars to add to the accomplishment.


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 12" versus 16" for galaxy structure new [Re: Mta472]
      #5678080 - 02/13/13 05:50 PM

It doesn't matter the degree of light pollution, the same benefits from an aperture increase accrue as they do under dark skies. If an object is seen in a smaller scope, more detail will be seen with a bigger scope. The brighter sky merely restricts to objects having higher surface brightness. Of course, beyond some amount of sky glow, practically nothing but the brightest central cores of galaxies is to be seen, with a concomitant dearth of interesting structure to be observed anywhere.

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azure1961p
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Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5678491 - 02/13/13 10:27 PM

+100 on what Glenn just said. Contrast thresholds don't take a holiday with poor sky's. a poor sky will never look pretty but everything else is the same in terms of resolving power which works on a number of levels. The laws of light are the same - city or country.

Pete


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deepskydarrell
member


Reged: 03/09/08

Loc: Abbotsford, BC Canada
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5678757 - 02/14/13 04:07 AM

Am I wrong, I've always equated a city view thru my 16.5 as about the same as a 4 inch in the dark? Perhaps that's too simplistic.

As for the larger the aperture the smaller the vehicle, the tendency may be the larger the aperture the farther one drives to the dark therefore the better fuel economy needed?

DSD.


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deepskydarrell
member


Reged: 03/09/08

Loc: Abbotsford, BC Canada
Re: 12" versus 16" for galaxy structure *DELETED* new [Re: azure1961p]
      #5678758 - 02/14/13 04:07 AM

Post deleted by deepskydarrell

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drbyyz
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Reged: 11/04/12

Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5679089 - 02/14/13 10:14 AM

Quote:

Am I wrong, I've always equated a city view thru my 16.5 as about the same as a 4 inch in the dark? Perhaps that's too simplistic.




I think a touch simplistic. Plus it really depends on what you mean by "city." My city sky is a Bortle 4/5, while someone else's may be a 9. Same with "dark" sky, mine is a 3, but others may have a 1.


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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5679109 - 02/14/13 10:24 AM

Quote:

Am I wrong, I've always equated a city view thru my 16.5 as about the same as a 4 inch in the dark?




That doesn't make sense to me. It seems to me that there are many things that will show far better through your 16.5-inch scope in the city than through a 4-inch scope in pristine skies. These are objects that are small but bright -- most obviously planets, but also many planetary nebulae and tight double stars.

Conversely, there are many things that will show far better in the 4-inch scope under dark skies than in any scope, no matter how big, in city skies. These include essentially all galaxies and diffuse nebulae.

The only place where aperture and sky brightness are even close to interchangeable is in the ability to see faint stars. But here, it seems to me that the 16.5-inch should show considerably fainter stars in the city than the 4-inch does under dark skies.


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Achernar
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Reged: 02/25/06

Loc: Mobile, Alabama, USA
Re: 12" versus 16" for galaxy structure new [Re: Starman81]
      #5679166 - 02/14/13 10:55 AM

Might be due to the cost of gasoline, and the fact bigger vehicles cost more to own in general. Still, it's really cool to be able to build a large Dob that will fit in many cars. I can get my 15-inch into my car, and still take along a passenger.

For every time I do take the 15-inch to a darker site, I use it at least several times at home despite the heavy light pollution. With digital setting circles and nebula filters, a lot of enjoyable observing can be done from a city at home. I have observed quite a good many galaxies from my driveway, even quite dim galaxies. Whether or not one is in a city or a dark site, a larger telescope always shows more than a smaller one at the same site.

Taras


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JohnH
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Reged: 10/04/05

Loc: Squamish BC Moved!!!!!
Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5679382 - 02/14/13 12:42 PM

The arguments for the step from a 12" to a 16" class follows good principles.

My current project is a 12 1/2" Dobsonian, which is a fair step up from my former go to scope, an 8" Maksutov. I want get some practice at a build while keeping weight under 60 lbs.

I chose this size as it meant about doubling the effective light gathered, which is roughly how much improvement is easily visible.

I was thinking that was where I would end telescope making,if it werent for a run in with a number of shorter, well corrected bunch of scope in the 16 to 22 inch sizes at some star parties.

So now I added 5 12 inch, 4 16 inch and one 18.625 blanks as fodder for larger, faster scopes in the future

Two of the 16s are full thickness, and I plan to send them to Glassfab to turn them into four 1.6 inch blanks more suited to portable instruments.

Edited by JohnH (02/14/13 12:59 PM)


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Ed D
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Reged: 04/30/10

Loc: Sunny South Florida
Re: 12" versus 16" for galaxy structure new [Re: Starman81]
      #5680163 - 02/14/13 08:25 PM

Quote:

Also, what's with people with big dobs always having smaller cars? It is a trend that I've noticed. It's like the challenge of hauling around a big dob wasn't enough so you want to try to do it with smaller and smaller cars to add to the accomplishment.




I don't think it's an astronomy trend or challenge as much as it is an overall social trend having to do with constantly fluctuating and elevating gas prices. While I miss my pickup truck I sure don't miss the all too frequent and expensive stops at the gas pumps.

Ed D


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure [Re: Tony Flanders]
      #5680453 - 02/14/13 11:56 PM

Tony you mean the 16.5" on virtually all galaxies and nebula? If not Id be interested in your take.

Thanks,

Pete


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