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Which would you rather have?

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#1 jrbarnett

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Posted 17 August 2014 - 06:29 PM

You're abducted off the street by hulking thugs, who silently drive you, head covered, to a rainy warehouse district in the city.  You hear a steel door roll open and then closed behind you, and are lead through a darkened hallway and pushed into a chair.  The hood is ripped away, and glaring light bombards you forcing you to squint.  As your eye adjust, you see the scrawny little rat-like man with a "Snidley Whiplash" style mustache sitting across from you behind a gray metal desk.  He says "choose".

 

The thugs lay two telescopes on the desk between you and rat-man.  One is a Vixen NA 140SS Neo Achromat and the other is an Astrotelescopes 152mm f/5.9 achromat.  The man repeats the command, "Choose" and adds "no cost to you, no strings attached, but you may choose only one."

 

Which one do you choose, and why?

 

Thanks,

 

Jim



#2 tomcody

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Posted 17 August 2014 - 07:03 PM

The Vixen, its lighter and easier to run away with!   :bigshock:

Rex


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#3 ThomasWos

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Posted 17 August 2014 - 07:36 PM

I would choose the Vixen. Better figure?

 

Tom


Edited by ThomasWos, 17 August 2014 - 07:37 PM.


#4 herrointment

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Posted 17 August 2014 - 07:44 PM

I've got a Synta 6" f/8 already. I'd choose the Vixen...because it's something different.

 

I'd be worried about Nell. Is the 5:20 freight running on time?


Edited by herrointment, 17 August 2014 - 07:45 PM.


#5 John Anthony

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Posted 17 August 2014 - 07:44 PM

  Well the abduction sounds like something that happens here in Detroit everyday without the happy ending, that being said I would take the Astrotelescopes 152mm, why?? for a refractor thats free I'll take the most aperture I can get, even if the 140 has better color correction. By the way I just wanted to add those are my kind of thugs. 



#6 LewisM

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Posted 17 August 2014 - 09:25 PM

Vixen.

 

Having looked through many an NA140SS, they are tempting. If I was pure visual, I would. 



#7 BigC

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Posted 17 August 2014 - 11:59 PM

I've got a Synta 6" f/8 already. I'd choose the Vixen...because it's something different.

 

I'd be worried about Nell. Is the 5:20 freight running on time?

Same here.



#8 csrlice12

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Posted 18 August 2014 - 12:41 AM

I choose to join his astro club!



#9 beanerds

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Posted 18 August 2014 - 06:59 AM

Aperture rules , the 152mm Achro thank you .

Brian.



#10 Don Taylor

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Posted 18 August 2014 - 07:11 AM

Well - an interesting question especially since you (Jim) and I both own the Astrotelescopes.

For quite a while I've considered the NA140 and really would like to have one BUT what has usually stopped me is the cost. Then the AT came off of HOO and CT's websites and shortly a 152 came up in the Cloudynights Classifieds so I bought.

I've really enjoyed it so far and posted a short report here from this year 'a Texas Star Party.

Actually - I had strongly considered both and ended up with the 152 more by luck than anything else. I'm planning on keeping mine. Btw - I had no personal experience with either one before buying - just the dialog and opinions here on CN.

140 advantages (which I'm sure you are aware of) - slightly less weight, flat field, somewhat less CA, slightly less fl or slightly greater TFOV. Looks great!

Disadvantages - slightly less aperture, uses proprietary Vixen parts, about double the price new, focuser not quite as good (if the 152 has the SV unit), don't believe the dewcap retracts.

#11 Mark Costello

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Posted 18 August 2014 - 07:42 AM

The Vixen would be my choice.  I believe I could tolerate the chromatic aberration based on current experience and it's lighter and handier.  It's only disadvantages are that it's twice as expensive and I might be worried about whether I'd ever have to collimate a Petzval refractor.



#12 Jon_Doh

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Posted 18 August 2014 - 09:15 AM

The Vixen.  Better CA management and not that much less aperture.  Plus, as others have said, it's smaller, lighter and therefore easier to set up.


Edited by Jon_Doh, 18 August 2014 - 09:16 AM.


#13 jrbarnett

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Posted 18 August 2014 - 09:48 AM

Interesting perspectives so far.  As Mr. Taylor points out, I already own a 152mm f/5.9, and like Don, the Vixen was the scope I cross shopped before buying the Astrotelescopes.  I've used the Vixen a couple of times, so perhaps I had a bit more context, but the Vixens I've used were both in relatively poor collimation.  My understanding is that Vixen has licked this issue in the more recent builds (these were units made several years ago; not the latest run).

 

The factor eliminated by the scenario is the price difference.  New, the Astrotelescopes 152 was about $1000.  The NA140SS is now no longer on sale and the new price runs about $2000.

 

Having used examples of both scopes, price aside, the Vixen is better made and better built.  I agree that the SV25 focuser is a little better than the Vixen's unit.  But the Vixen has an appropriately long dew shade, retractable or not; the Kunming unit's dew shade is woefully short.  The Kunming is also quite heavy for its aperture, and extremely front heavy despite being a doublet.  The Vixen is the easier mounter.  The 12mm of additional aperture is a plus in favor of the Kunming, but here's the thing.  The Kunming performs best at lower magnifications.  Using lower magnifications reduces the limiting magnitude of a given aperture.  To take advantage of the greater light grasp of the Kunming, you have to use magnifications that induce lots of false color on targets magnitude 2.5 or above.  The NA140SS actually goes deeper before the false color becomes intrusive.  Because the Vixen is a fast achromat and also yields false color, the flat field pitch isn't a selling point for me.  The level of FC in the 6" f/5.9 doublet is much less than that in a standard SCT, by comparison.  Really not much of an issue visually, and I wouldn't choose the Vixen for imaging (though some do).

 

For me these RFT achromats are really a niche scope; a nifty combination of a relatively wide, high contrast field with more light grasp than the typical extremely short focal length small aperture wide field scopes.  So I bought based on price.  I didn't want to make a huge investment in a limited-purpose scope.  But were price not a factor, I'm not sure that I wouldn't have gone with the Vixen.

 

- Jim



#14 Scott in NC

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Posted 18 August 2014 - 10:03 AM

I'm thinking that the doublet might be less likely to go out of collimation than the Petzval if I have to use one of them as a club to fight my way out of that scenario. :grin:



#15 BillP

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Posted 18 August 2014 - 10:04 AM

Vixen NA 140SS.  Flatter field, less color.  Would trade the extra aperture for the better controlled fov.  Plug get a tad more TFOV - 20x and 3.34 deg TFOV from a 40XW.  I've had fast 6" achros before and while they are great for wide fields and even high powers on DSO, if any planet or bright star enters the FOV, or the Moon, CA is just too distracting and damaging.  The Vixen though should be able to handle the bright objects with managable CA.



#16 SteveG

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Posted 18 August 2014 - 12:58 PM

I would choose the Vixen for its flat field.



#17 Don Taylor

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Posted 18 August 2014 - 01:40 PM

Jim: I think you and I are singing from the same hymnal. I wanted the vixen but not badly enough to spend the considerably more $$$$.

#18 maadscientist

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Posted 18 August 2014 - 01:45 PM

Vixen NEO 140. I have 2 narrowband images done with it in the Vixen Website.

http://www.vixenopti...ors/neo140.html

 

The scope can be used for RGB, believe it or not.

 

However, there is a big price difference. I did those narrowband shots with the Chinese version, which I got much cheaper than the 2K asked for now.

 

Want to stir the pot? I have a Celestron XLT 150 f5 that I am testing. These scopes were part of a package deal from Celestron, but the tubes can be had for under $500.I did some daytime shots and lunar shots that I will process tonight, but the smoothness of the optic was impressive.

 

Dan L


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#19 Stelios

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Posted 18 August 2014 - 01:57 PM

  Using lower magnifications reduces the limiting magnitude of a given aperture.  

 

Isn't that only true when the exit pupil becomes huge (thus wasting some light?) On a 900mm scope, I'd expect CA to be quite decent with a 20mm EP yielding 45x and about a 3.38mm exit pupil, which should be all useful even to aged eyes. For extended objects such as the Veil, I can't see any disadvantage here. 

 

Just the same, I'd have selected the Vixen given the initial choice. I've had an 152mm F/6 achromat many years ago, and it is *only* useful for deep sky at low powers. I just don't see the need to justify if not the purchase price, the time to set it up. 



#20 jrbarnett

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Posted 18 August 2014 - 02:05 PM

 

  Using lower magnifications reduces the limiting magnitude of a given aperture.  

 

Isn't that only true when the exit pupil becomes huge (thus wasting some light?) On a 900mm scope, I'd expect CA to be quite decent with a 20mm EP yielding 45x and about a 3.38mm exit pupil, which should be all useful even to aged eyes. For extended objects such as the Veil, I can't see any disadvantage here. 

 

Just the same, I'd have selected the Vixen given the initial choice. I've had an 152mm F/6 achromat many years ago, and it is *only* useful for deep sky at low powers. I just don't see the need to justify if not the purchase price, the time to set it up. 

 

Using lower magnifications reduces the limiting magnitude of a given aperture.

 

Nope.

 

You can play with any of the various limiting magnitude tools online and model in either telescope.  You'll see, for example, that, at 40x the 6" has a limiting magnitude of 12.6.  Bump it up to 140x, and the limiting magnitude jumps to 13.9 (assume Mag 5 starting skies).  Put even a third magnitude star in the field of the f/5.9 at 140x, and there will be some false color that I'd call irritating.

 

http://www.cruxis.co...ngmagnitude.htm

 

- Jim



#21 choran

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Posted 18 August 2014 - 03:45 PM

Jim, what I want to know is:  Do they still have you in the warehouse? 



#22 russell23

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Posted 18 August 2014 - 05:01 PM

Jim.

 

I have the Vixen 140NA.  I have never looked through a 152 f5.9 achromat so I cannot say.  The flat field of the Vixen is very nice.  I tried a Celestron 150mm F/5 and it made a mess of eyepieces.  The Vixen 140 is far better with eyepieces such as the 20mm XW.  So I have to think the Petzval design does have value.  

 

Dave



#23 David Pavlich

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Posted 18 August 2014 - 05:08 PM

Vixen...nice views and really nice build quality.  An easy choice for me.

 

David



#24 jrbarnett

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Posted 18 August 2014 - 07:37 PM

Jim, what I want to know is:  Do they still have you in the warehouse? 

Whaddya mean Chuck?  I'm the rat-man on the other side of the desk.  :lol:

 

- Jim



#25 choran

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Posted 18 August 2014 - 08:00 PM

 

Jim, what I want to know is:  Do they still have you in the warehouse? 

Whaddya mean Chuck?  I'm the rat-man on the other side of the desk.   :lol:

 

- Jim

 

OK buddy!  LOL  I thought maybe this was real and they'd given you one text message to the outside world!  LOL








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