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neil groves

aperture importance?

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I will be purchasing a new scope in the new year for observing, my question is that I am currently using a 120ED skywatcher, I would like to know if it is a worthwhile upgrade to an 8" or 10" Newt as far as open and globular star clusters are concerned? is the resolving power of the extra aperture worth the $800 outlay?

At the moment taking M13 as an example, I can see it as a patch of light with a few single stars scattered around the perimeter, would the extra aperture resolve this to any great degree?

anyone with experience please can you advise, particularly those that have done a comparison of the two?

Neil.

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M13 is a great example to use. In my 6" Newt it looks like a fuzzy blob with a few bright stars around the outside, much like the picture you have posted above. In my CPC1100 or my 12" Dob I can see hundreds of thousands of bright points and only a small core area is fuzzy.

Size matters :wink:

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M13 in deep dark skies provides a stunning view in a 4" frac. Like other clusters, it looks like diamonds on black silk.

It gets really bleached out by any background light pollution, this leads to lack of contrast. It's not worth going aperture mad with light pollution to deal with,

Nick.

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I have an ED120. It's a really good scope for the moon, planets and double stars but it can't compete with larger aperture scopes on deep sky objects. Globular clusters in particular seem to show immediate benefits from increased aperture, the brighter ones appearing almost like their photos under dark skies with a 10" or larger scope as Qualia's excellent and accurate sketch portrays.

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I also have an 120ED and a 12" Dob.

The 12" Dob easily beats the 120ED when it comes to DSOs but the 120ED comes on top with tight Doubles.

Avtar

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M13 just does get 'better with bigger' provided the optical quality holds up. But our top quality 5.5 inch TEC apo cannot compete on M13 with our optically only average 20 inch Newt. 

Olly

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On objects like globs aperture makes a huge difference as resolving stars is what aperture does. The bigger that scope the fainter and fainter the stars that can be made out. 

Whilst a 120ED does show M13 quite nicely from a dark sky a 10" will beat it hands down. 

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Am I going to get any benefits if I chose to image with the larger aperture later on? will I get more detail in an object or is that just down to exposure time? I have seen stunning images made from 80mm scopes.

Neil.

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10-12-14 and even possibly 16 Inches Go for it.

Larger than this and you may have to look at what your sky will do for you. Huge apertures can magnify the wobblyness of

slightly wobbly skies just like too much magnification can.

Having said that,  if someone were to give me a 24 inch Dob I would just try to cope with it " muddle through" thats what I say.

Mick

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Am I going to get any benefits if I chose to image with the larger aperture later on? will I get more detail in an object or is that just down to exposure time? I have seen stunning images made from 80mm scopes.

Neil.

A larger aperture will give you a greater image scale hence a larger image at any given focal ratio. If you were to compare a 4 inch F4 telescope with an 8 inch F4 telescope the image would have the same brightness but the image in the 8" would be twice the size and at a more simplistic level would be able to show more detail. That is why for small faint deep sky objects you need a fast mirror like F5 (bright image) & lots of diameter (so image is big & detailed).

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Am I going to get any benefits if I chose to image with the larger aperture later on? will I get more detail in an object or is that just down to exposure time? I have seen stunning images made from 80mm scopes.

Neil.

Forget aperture when thinking about imaging. The two primary numbers to think about are

Focal length - which determines what will fit on your chip.

Focal ratio - which determines exposure length.

Reality also says that a long focal length will be much harder to guide and that a fast focal ratio scope with a long focal length is going to be a very big scope and will need a lot of mount!

Olly

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I have a dobson telescope and I know how powerful it is I have only the 10mm and wide angle. Lenes I got in to look deeper night sky by looking at the faintes stars I can see on a good night it goes deep I was just wanted to know how deep can this telescope can go with the right lenes it's 8inch dobson telescope thank you Bugfly

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I have a dobson telescope and I know how powerful it is I have only the 10mm and wide angle. Lenes I got in to look deeper night sky by looking at the faintes stars I can see on a good night it goes deep I was just wanted to know how deep can this telescope can go with the right lenes it's 8inch dobson telescope thank you Bugfly

You can see the quasar 3C 273. At two billion light years distance in an 8" scope, deep enough for ya? :)

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You can see the quasar 3C 273. At two billion light years distance in an 8" scope, deep enough for ya? :)

no can we go deeper only jokeing lol thanks for your help mate
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At the moment taking M13 as an example, I can see it as a patch of light with a few single stars scattered around the perimeter, would the extra aperture resolve this to any great degree?

anyone with experience please can you advise, particularly those that have done a comparison of the two?

Neil.

Check out the M13 comparison diagram here :-

http://www.obsessiontelescopes.com/m13/index.php

That page accurately depicts the brightness and resolution of M13 in various scopes from 8" through to 25". 

Take the 8" and 12.5" representations as what you could expect to see from a good dark sky with a moderate to large aperture scope. As you can see, extra aperture will always give you a brighter image with more resolution providing your skies permit.

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For me, I don't think that M13 is a particularly good example of light gathering, the difference shown in the Obsession page between an 18" and 25" aperture would not encourage me to pay the extra. Now if there was a blank circle for the 18" and a group of galaxies shown in the 25" aperture circle then that might be a different matter.  :smiley:

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Bright Globulars are much better with more aperture whether you have light pollution or not. Galaxies get easily washed so, so you may be able to see a few more but it wont make a great difference. M13 from my very light polluted garden and my 10" is a big improvement than a 6" under dark skies.

I never managed the veil from my back garden with my old 6", but can just make it out with the 10".

Edited by bish
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Bright Globulars are much better with more aperture whether you have light pollution or not.

yes

i sold my light weight 4"  achro (9Kg) and buy a heavy 8" on eq5 (40Kg) just for Globulars !

i am waitng for end of winter for M13

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yes

i sold my light weight 4"  achro (9Kg) and buy a heavy 8" on eq5 (40Kg) just for Globulars !

i am waitng for end of winter for M13

For a fun winter glob try for M79. It's pretty low down and will require a good southern sky but worth having a bash at :)

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Just my 2 cents worth.

Your 120ed with a reducer / flatner will be great for imaging.

For observing a large DOB 300+ is fantastic, but won't be any good for imaging.

So it depends if you want two rig's.

Last option depending on your mount, is to go for 200pds on your mount which will be good for imaging, but only marginally better for observing.

Edited by Christopher Davenport

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For a fun winter glob try for M79. It's pretty low down and will require a good southern sky but worth having a bash at :)

yes i know it, but southern sky of my house is closed by a big beautiful wall !

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