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Which aperture is best?


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Hello All! 

  Currently, I have a Meade ETX 90 telescope. I really like it and get great views of the moon and planets out of it. However, I am hoping to upgrade to a large reflector.

  I am looking at various scopes ranging from the Orion SkyQuest XT8 to the forbiddingly pricey Orion SkyQuest XT12i Intelliscope. I know that aperture is one of the most important things to consider in a telescope, but I also realize that people can get "aperture fever" and go for scopes that are unnecessarily large.

  I am wondering; Is a bigger aperture worth the price jump from 8'' to 10'' or from  10'' to 12''? How much more will I be able to see?  I have heard that the best telescope for a person is dependent on the kinds of things they want to observe. I don't really look at deep sky objects (though I am getting increasingly interested in them), and mostly enjoy the moon, planets, and a few double stars. I want a telescope that will accommodate this, but is also able to have a great grasp on deep sky objects.

  Honestly I think I am on the right track with the scopes I am looking at, but I really want some advice on which size is best for me. What do you think?

  Thanks for the advice!

 

 

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If you're primarily interested in the moon planets and double stars then aperture is less of an issue than it would be on deep sky targets. Although increased aperture does lead to higher theoretical resolution the atmosphere will be the limiting factor with anything above about 8" especially in the UK. Ease of set up is another major factor. the bigger it is, the harder it will be to set up, the longer it will take to cool down and unless you're very dedicated, the less you may feel inclined to use it. I've tended to observe with scopes in the 4 to 8" range, though I've used scopes up to 30"! My experience has been that you need to double the aperture to make an "oh wow" difference - and that can get very expensive very quickly! I was looking at Jupiter once from a great site overseas with a variety of scopes. The best view was through a 7" astrophysics refractor - an 18" newtonian net to it was good too but there was no more to see than in the 7" and the contrast was ever so slightly less. However the ring nebula through the 18 was very much better than in the 7 :)

Edited by timwetherell
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I agree with Tim, From what I've gathered aperture is king as it immediately affects the amount of light that it can gather. though if you're not so much interested in Deep Sky then a smaller aperture might still suit you perfectly. I mean you can still see a lot of the brighter deep sky objects even with a smaller aperture:)

46 minutes ago, timwetherell said:

If you're primarily interested in the moon planets and double stars then aperture is less of an issue than it would be on deep sky targets.

 

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My husband had an ETX105 and upgraded to an LX90 10inch. It was a bit heavy if you need to carry it in and out but it was very good especially with globular clusters and planetary. I had a Celestron 8SE which was also good and had the advantage that it broke down to 3 sections that were easy to handle.  Also you can use the mount for other short telescopes such as a solar scope. Though I liked my 8SE on a CG5 mount, it had fewer backlash issues and was more stable as well as enabling larger eyepieces to be used as the telescope tube can be balanced better.  You can also upgrade the scope to something else, I eventually switched to refractors for imaging.

If you're into visual, I don't think you could do much better with something like the above. And they work similarly to your ETX.

Anne

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10 hours ago, Subdeo said:

I don't really look at deep sky objects (though I am getting increasingly interested in them), and mostly enjoy the moon, planets, and a few double stars

The question here is whether you enjoy those things because that is your interest, or because those things happen to be the strengths of your current telescope. If it really is lunar and planetary that interest you most with a small amount of DSO observation thrown in then aperture is not quite as important and so the 8" or even a Mak/SCT would be good choices. On the other hand if you think you would really like to observe DSOs, but it is just the small aperture of your current scope holding you back, then go for the biggest one that you can easily take out under the stars. An 8" under the stars will show you much more than a 12" in storage because the effort of setting it up prevents you getting it out.

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Thanks everyone! I have another question. What do you think about cooling fans? Do they really help? I am trying to decide between the Apertura AD10 (1st link) and the Orion SkyQuest XT10 (second link). What do you  think?

https://www.highpointscientific.com/apertura-ad10-10inch-dobsonian-telescope-ad10?utm_source=google&utm_medium=cse&utm_term=APT-AD10&gclid=EAIaIQobChMIqZPx_6X71QIVQgOGCh1pTwIcEAkYESABEgLLhfD_BwE

 

http://www.telescope.com/Telescopes/Dobsonian-Telescopes/Classic-Dobsonians/Orion-SkyQuest-XT10-Classic-Dobsonian-Telescope/pc/1/c/12/sc/13/p/102006.uts

 

Before I buy though, I plan to go to an event where these scopes are to see them for myself and make sure I want the 10'' over the 8'' versions. Lastly, is the focal ratio important? The Apertura has one that is .2 higher. Thanks!

P.S. The reason I haven't looked for DSOs much is because I really haven't known how to find them in the past.

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I don't want to polarize this but my 8" I find it very heavy ):  but maybe it's only a negative state of mind, I have to climb steps too. In my actual condition, 8" is the bigger I am willing to carry, 10" is scary, first time I saw one, I was intimidated by it and still is.

Like the Sensei used to say while doing wall sit with a another person sitting on our legs? or wearing a 220 lbs person and squat walking around the gymnasium? Pain is only a state of mind he said :p ... crazy man.

 

 

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Climbing a number steps with a scope puts a whole different spin on the weight and portability of a scope. I have a short, flat carry to my observing place so moving my 12" do there in two short carries is no problem - it takes just a minute to set the thing up. If I had to climb up and down some stairs it would not be practical at all for me.

Each of our circumstances is a little different and it's taken some time to realise what works for me. My previous 12" dob was a Meade Lightbridge which was much heavier than my current Orion Optics 12" dob. Ergo, the Meade did not get used much :rolleyes2:

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I have a Dark Star (remember them?) 12" which when I moved house became less useable as street and neighbours' lighting made moving it around necessary and handling precarious. Still have it & dream of a dark site of my own.

Bought a C8 to replace it about 20 years ago, but there is no replacement for displacement! Much more portable though.

Yesterday I bought a 10" F5 1270mm Bresser Messier dob which I hope will be my new DSO eye to the sky, due tomorrow (wanted to stay with solid tubes. ?

 

Edited by 25585
Clarity
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23 minutes ago, John said:

I do remember Dark Star - I have a brochure of theirs somewhere I'm sure :icon_biggrin:

About the only affordable big aperture scopes a couple of decades back.

www.darkstartelescopes.blogspot.co.uk/2012/07/dark-star-html?m=1

Mine is hammerite blue

 

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As for which size of aperture is best with regards to 8, 10, or 12 inches which you are considering ?

I believe it depends more on the quality of the optics than just size, as resolution will only be as good as the weakest link in the optical train.

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On 30/08/2017 at 00:36, Subdeo said:

Thanks everyone! I have another question. What do you think about cooling fans? Do they really help? I am trying to decide between the Apertura AD10 (1st link) and the Orion SkyQuest XT10 (second link). What do you  think?

https://www.highpointscientific.com/apertura-ad10-10inch-dobsonian-telescope-ad10?utm_source=google&utm_medium=cse&utm_term=APT-AD10&gclid=EAIaIQobChMIqZPx_6X71QIVQgOGCh1pTwIcEAkYESABEgLLhfD_BwE

 

http://www.telescope.com/Telescopes/Dobsonian-Telescopes/Classic-Dobsonians/Orion-SkyQuest-XT10-Classic-Dobsonian-Telescope/pc/1/c/12/sc/13/p/102006.uts

 

Before I buy though, I plan to go to an event where these scopes are to see them for myself and make sure I want the 10'' over the 8'' versions. Lastly, is the focal ratio important? The Apertura has one that is .2 higher. Thanks!

P.S. The reason I haven't looked for DSOs much is because I really haven't known how to find them in the past.

+1 for 10", or 12" if you can manage it ;)

If viewing planets/moon, I let my f4.7 10" (SW 250px - cheaper than Orion) cool for 40mins without any fans.  For DSOs at lower power, I can start observing pretty much straight away.

I'm 41 and thankfully healthy - and find my 10" no bother to carry - grab and go.

I'm very happy that I went for the 10" for observing DSOs: I was originally going to go for the 8".

Add a Telrad, and you'll be finding DSOs no prob with Sky Safari from decently dark skies.

I wouldn't be concerned too much about the difference in f ratio.

Best of luck with your decision - I'm sure the views through any of these scopes will delight you :)

-Niall

 

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On ‎8‎/‎30‎/‎2017 at 16:38, celestron8g8 said:

12" would be nice but if too big for you go with a 10" . Aperture is your friend just for observing . 

Aperture increases brightness and resolution (detail). Don't consider  the difference in aperture diameter as much as the difference in area of the mirror, which increases as a square function of diameter. My C8 collects almost 45% more light than my C6, from a "mere" 2 inches difference in diameter.

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1 hour ago, Luna-tic said:

Aperture increases brightness and resolution (detail). Don't consider  the difference in aperture diameter as much as the difference in area of the mirror, which increases as a square function of diameter. My C8 collects almost 45% more light than my C6, from a "mere" 2 inches difference in diameter.

Been knowing what you said for the last 25 yrs . But what is your point , are you not understanding or are you just adding to what I already know but didn't mention ?

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2 hours ago, celestron8g8 said:

Been knowing what you said for the last 25 yrs . But what is your point , are you not understanding or are you just adding to what I already know but didn't mention ?

Even though I quoted you, it was more addressed at the OP, maybe he didn't know, since he's asking about diameter.

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22 minutes ago, Luna-tic said:

Even though I quoted you, it was more addressed at the OP, maybe he didn't know, since he's asking about diameter.

Well usually when you quote someone the message is directed at the one you quoted so since you quoted me I take it your directing your reply to me since you did not mention the OP . 

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  • 2 years later...

     "Aperture fever" is just people trying to justify smaller scopes & limiting themselves.  Forget that, if you can afford an 8-12 inch DOB, get one. The magnitude differences are: 

  1. 12 in= 14.9
  2. 10 in= 14.5
  3. 8 in= 14.0

In using, Area= 3.14 x d2/4, the light gathering power for each is: 

  1. 12 in (305 mm)=     73,024 mm        113 in        Large Scope            Large DOB
  2. 10 in (254 mm)=     50,646 mm          78 in        Medium Scope       Medium DOB
  3. 8 in (203 mm)=       32,349 mm          50 in        Medium Scope       Medium DOB
  4. 3.5" (90 mm)=         6,358 mm              9 in        Small Scope           -

     Science does not lie, it isn't an opinion. You need the aperture fever, to keep progressing because eventually, you will need to resolve & see detail, which means, you then know more, about objects. After reading your post, Id'e definitely go, with the 12 inch. However, I would pass on the Push-To and use two other options. (1) Get a classic, with an aftermarket tracking base or just (2) get the GOTO. The GOTO is not worth the extra $1,000. What did you end up getting? 

 

 

 

Edited by Science562h
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