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axle01
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Reged: 01/26/13

Loc: Townsville Nth Qld Australia
305 Newt v 130mm refractor
      #5843042 - 05/06/13 07:45 AM

I have a 130mm Refractor Triplet 920mm focal length F7 and looking to get a 305mm Newtonian 1200mm F4 (below) what could I expect to see and image with the Newt that I can't do with the Refractor.

http://www.zwoptical.com/Eng/Optics/305/index.asp

Any advise would be appreciated.

Alan


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csrlice12
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Reged: 05/22/12

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Re: 305 Newt v 130mm refractor new [Re: axle01]
      #5843159 - 05/06/13 09:42 AM

Unless the refractor is an APO/has ED glass, you'll have CA (purple fringing) on planets and bright objects. Beautiful Truss Newt, hadn't heard of that company, you'll have to let us know how the scope performs. That mount does look a little light for that big of a scope (even though its a truss and withing the mounts weight limit), especially if going for AP. It looks like a CG-4?

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GlennLeDrew
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Re: 305 Newt v 130mm refractor new [Re: csrlice12]
      #5843382 - 05/06/13 11:58 AM

You will enjoy 2.3X better resolution and 5.5X more light grasp.

In slightly more detail. At given exit pupil and object surface brightness, you can see objects 2.3X smaller. At given exit pupil you will see stars nearly 1.9 magnitudes fainter.


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axle01
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Reged: 01/26/13

Loc: Townsville Nth Qld Australia
Re: 305 Newt v 130mm refractor new [Re: csrlice12]
      #5844115 - 05/06/13 06:07 PM

Quote:

Unless the refractor is an APO/has ED glass,




This is a copy & paste of the refractor I have.

The United Optics ULT 130 Triplet APO Refractor Telescope is an Ultra Premium 3-element, air-spaced Fluorite apochromatic design. It has a 130mm aperture and 920mm focal length which operates at f/7.


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Hermie
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Reged: 04/20/05

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Re: 305 Newt v 130mm refractor new [Re: axle01]
      #5844167 - 05/06/13 06:31 PM

Alan,

The real strength of a refractor is their ease of use, in my opinion. Put it on a mount, slip in an eyepiece, and focus. That's it.

There is no doubt that larger newt will provide brighter views with higher resolution. The newt will do much better on deep sky in particular. But be prepared to spend some time collimating and cooling your scope. A large newt and smallish refractor complement each other well.

Hermie

Edited by Hermie (05/06/13 06:33 PM)


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RAKing
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Re: 305 Newt v 130mm refractor new [Re: axle01]
      #5844230 - 05/06/13 07:11 PM

That is an interesting scope. I just wish they could spell "Newtonian" on their website.

That mount looks very much like an EQ5 or EQ6, but the tripod legs have been shortened from the stock versions. That has always been my biggest issue with mounts these days. The tripods rarely collapse enough for easy ergonomic access with a Newt. I have a 24 inch portable pier that I can use with my Newt on the Mach 1 -- but doing a polar alignment on that thing is difficult. If I was going to use it regularly, I would invest in one of Roland's right-angle polar scopes ASAP.

As mentioned above, the 12 inch Newt will go a lot deeper than the 5 inch refractor. You can make up for some of that aperture by upgrading your imaging mount (tracking and guiding) and doing longer subs with your refractor. Plus, that Newt's structure looks so flimsy, I'm not sure I would trust it for imaging. Visually, there's not much any of us can do to make up for that much aperture and the big Newt will win easily.

If you do pick up this Newt, please let us know how it works for you.

Cheers,

Ron


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axle01
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Reged: 01/26/13

Loc: Townsville Nth Qld Australia
Re: 305 Newt v 130mm refractor new [Re: RAKing]
      #5844728 - 05/06/13 11:47 PM

Thanks guys, Ron I have a AZ-EQ6-GT mount so that part is good, now all I've gotta is convince the better half I need it.

Alan


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daniel_h
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Reged: 03/08/08

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Re: 305 Newt v 130mm refractor new [Re: axle01]
      #5844845 - 05/07/13 01:54 AM

i think a 10" is more manageable for a mounted ota rather than 12"

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axle01
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Reged: 01/26/13

Loc: Townsville Nth Qld Australia
Re: 305 Newt v 130mm refractor new [Re: daniel_h]
      #5844908 - 05/07/13 04:53 AM

They have a 6"-8"-10"-12" and a 15" on the way.

http://www.zwoptical.com/Eng/Optics/254/index.asp

Alan


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Eddgie
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Re: 305 Newt v 130mm refractor new [Re: axle01]
      #5845126 - 05/07/13 08:58 AM

A 12" telescope with good mirrors will show you much more in just about any kind of target.

Here are some examples. Objects like the Orion Nebula will reveal more stars in the Trapezium, and also imbedded in the nebula you will see tiny, faint stars here and there that don't show up in smaller apertures.

At high power, the nebula itself will reveal much more structure.

Likewise for planetary nebula. Targets like the Ring Nebula start to show much more defined structure. The "Smoke Ring" starts to look less like a perfect ring and more like an exploding nebula with a larger apeture.

Galaxies will typically extend further, and once again, may start to show more distinct structure. Knotting or rifts in some galaxies that are hinted at in smaller apertures become more defined.

Globulars will perhaps show the biggest possible change. Using a 5" or 6" aperture, most globulars will not resolve very well at the core. Individual bright stars will show across the core, but many times, the core itself will simply be a glow.

In a 12" aperture, the core of most of the larger globulars will start to resolve and not be a smooth glow. This is the deep sky target where I think it is easiest to see the aperture advantage.

Planets.. Depends on your patience. If you are patient, you will resolve far more structure on planets. Faint ovals on Jupiter become common rather than almost never. The eddy structure following the GRS starts to look more like it does in pictures. Faint Festoons start to extend much deeper into the equitorial regions.

In years gone by, I would have said "Coma will be a factor" but with Paracorr, no longer. You can get pinpointy views in a fast Newt now. It might cost you a bit of focal lenght, but you have the option of going native, or going clean.

For imaging, everything above, but the biggest difference is that everything will be bigger. Of course that means that some targets like very large nebula will not fit into the field.

I find there to be far more difference in telescope performance based on apeture than on optical design.

All the endless rants about obstructions, cooling, field of view, and off axis performance to me completely cloud the overwhelming virtures of apeture.

Your refractor will be a nice complement to a larger reflector, but regardless of the target you aim at, if it fits into the field, you will see more of it or more detail in it in the 12" scope.


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axle01
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Loc: Townsville Nth Qld Australia
Re: 305 Newt v 130mm refractor new [Re: Eddgie]
      #5846247 - 05/07/13 06:07 PM

Thanks Eddgie I will have to show this to my better half it may help convince her that I really need it.

Alan


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izar187
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Reged: 09/02/06

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Re: 305 Newt v 130mm refractor new [Re: axle01]
      #5847658 - 05/08/13 12:21 PM

Active cooling for a newt this size is pretty important. Vibration free. For during observing, not just before. An awful lot of the seeing issues with larger newts are inside the ota, and at the mirror surface.

A shroud for the truss tube structure is rather important too.

Ep position will get interesting non ergonomic also, when observing certain parts of the sky.

The upper truss structure will need to be rigid enough to support the bino-viewer and ep's. To keep things in collimation.


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csrlice12
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Re: 305 Newt v 130mm refractor new [Re: izar187]
      #5847848 - 05/08/13 02:05 PM

Looks like there's not a lot to cool outside of the primary, and all exposed like that, it should cut down on the time.

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davidpitre
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Re: 305 Newt v 130mm refractor new [Re: Eddgie]
      #5848718 - 05/08/13 09:00 PM

Quote:


I find there to be far more difference in telescope performance based on apeture than on optical design.





Yep.


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beanerds
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Reged: 07/15/08

Loc: Darwin Australia
Re: 305 Newt v 130mm refractor new [Re: csrlice12]
      #5851650 - 05/10/13 09:46 AM

Quote:

Unless the refractor is an APO/has ED glass, you'll have CA (purple fringing) on planets and bright objects. Beautiful Truss Newt, hadn't heard of that company, you'll have to let us know how the scope performs. That mount does look a little light for that big of a scope (even though its a truss and withing the mounts weight limit), especially if going for AP. It looks like a CG-4?



Are we looking at the same photo ? the 305mm spider like , truss , 12kg newt ? .
I think thats an EQ6 style mount , plenty strong enough , just look at the lack of counter weights .
Nice set up .
I would be happy with one .
Brian.


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