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Visual Only: 150mm Triplet APO vs 14" Dobsonian

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108 replies to this topic

#26 noisejammer

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Posted 25 July 2018 - 12:37 PM

I've previously reported running my TOA150 up against Cotts' 12" with Lockwood optics.

 

On large structures - say like the Pleiades or other things bigger than a degree across and maybe the moon, the Tak wins. On everything else, the Dob wins easily.

If you want to shoot images, the Tak wins on everything (but you don't want to shoot images.)

If you want to put it in your car, it's roughly a draw - the Tak is smaller but it demands a considerable mount.

 

If you want to draw a lineup make new friends at a star party .. the Tak will supply all weekend.


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#27 Seiko4169

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Posted 25 July 2018 - 12:38 PM

I had the C14 edge and 130 Tak apo. I’ve now sold the C14 and have just purchased a TOA 150 to compliment the very wide fields of the 130. Although similar the lure of the perfect planetary and double star views of the TOA 150 are what I’m after.

The C14 brought globulars to life and deep sky objects became much easier to see however the seeing got in the way a lot. The stars where never a tight or as crisp as the Takahashi’s and ultimately my personal preference opted for clarity. I might at some point get a larger Mewlon or C14 in the future to ensure I have the option but my current viewing habits prefer the pristine views of the Takahashi’s.

Edited by Seiko4169, 25 July 2018 - 12:55 PM.

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#28 starman876

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Posted 25 July 2018 - 01:04 PM

another refractor versus mirror scope threadwaytogo.gif

 

is there ever a winnerlol.gif


Edited by starman876, 25 July 2018 - 01:05 PM.

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#29 Astrojedi

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Posted 25 July 2018 - 01:09 PM

This is not a competition hence no "winners" as we are comparing apples to oranges. For me a refractor is not a substitute for a large dob and vice versa. What we are discussing here are pros and cons of each - and I think it is a good discussion.


Edited by Astrojedi, 25 July 2018 - 01:10 PM.

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#30 gnowellsct

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Posted 25 July 2018 - 02:49 PM

If one has the money to buy a 6" triplet apo and mount it properly one can afford a wide variety of alternative configurations.   

 

One of the ironic things about refractor design is what one might call the Conrady barrier.  This is the relationship between the size of the aperture and the difficulty in controlling chromatic aberration.  

 

The larger the aperture's diameter, the more difficult this correction is to achieve.  This pushes the boundaries in multiple directions.  For one thing, one needs more exotic glass (more expensive) and more of it (thicker lenses), which means rejecting more blanks (an additional component of cost).  

 

But the designer is also under constraint to limit the CA by pushing out the focal ratio.  

 

So one would think, well, the LARGEST refractors should have the SHORTEST focal ratios, because the mechanics of manipulating them would be much easier.   We should have f/4 or f/5 150 to 200 mm refractors.  But in reality, these scopes tend to push out on the FL: f/7, f/8, even, for TEC's 250 mm, almost f/9.  

 

So the optical design of the larger aperture increases the mechanical issues.  You need to mount it high and be prepared to go low to access the eyepiece at the best positions in the sky.  

 

You can be pretty sure if you are willing to pay these costs in cash for the optic, cash for the mount and pier, and inconvenience in terms of physically manipulating the scope, that you are a total refractor-holic and there is no point in arguing the matter about what is best because the answer is already known.  

 

By contrast, the pikers hang out at 140 mm and under and do such absurd things as say, "well this here apo stuff is interesting I guess I'll stick one on top of my SCT."  Or set one up next to my bigdob.  Whatever.  They all pikers.

 

Greg N



#31 Jon_Doh

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Posted 25 July 2018 - 02:51 PM

Not just brighter, but far more detailed. I've had views of planets through large Newtonians, notably Mars and Jupiter, under exceptional seeing that can simply not be duplicated through any 150mm apochromat. 

 

Clear skies, Alan

We don't get exceptional seeing where I live, so like Ron I'll take the refractor.


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#32 Jeff B

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Posted 25 July 2018 - 03:57 PM

I think we have to be careful with generalizations when commenting on APOs vs. Reflectors.

 

While I generally agree with what is being said we need to be careful to separate the subjective from the objective and also ensure we are comparing instruments of comparable quality / cost irrespective of design.

 

Subjectively, yes you could say the view in an ED apo is better but objectively a 14" will have significantly higher light grasp, resolution and contrast vs. a 6". There is just no competition.

 

One my second point....

 

My 14" has a high strehl mirror and a 19% obstruction secondary. It costed me the same as a premium 6" APO (but still much cheaper on a $ / aperture basis). With the coma corrector the views it produces are just sublime - pinpoint stars and no coma anywhere in the fov even with my 82deg 30mm. The airy disk is so tight it is almost indistinguishable from an apo.

 

In excellent seeing I can see festoons within festoons on Jupiter and swirling clouds within the GRS - views that are unmatched by any 6" apo. I doubt even a 8-10" apo will come close.

 

But I still use my 4" and 5" refactors and my C9.25 more simply because they are "easier" given my limited time. The 14" comes out on the weekends or on dark site trips. To me the refactors have a completely different value proposition.

Good Lord, you can see the airy disk from a 14" scope!?  Where do you live?  I want to live there.  Around here, 1 arc second seeing is the prayer for the night, many times unanswered. frown.gif



#33 Jeff B

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Posted 25 July 2018 - 04:00 PM

I've previously reported running my TOA150 up against Cotts' 12" with Lockwood optics.

 

On large structures - say like the Pleiades or other things bigger than a degree across and maybe the moon, the Tak wins. On everything else, the Dob wins easily.

If you want to shoot images, the Tak wins on everything (but you don't want to shoot images.)

If you want to put it in your car, it's roughly a draw - the Tak is smaller but it demands a considerable mount.

 

If you want to draw a lineup make new friends at a star party .. the Tak will supply all weekend.

Ok, I'll quibble a little bit here.  For lunar/planetary imaging, the 12" will eat the Tak alive.



#34 Astrojedi

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Posted 25 July 2018 - 04:18 PM

Good Lord, you can see the airy disk from a 14" scope!?  Where do you live?  I want to live there.  Around here, 1 arc second seeing is the prayer for the night, many times unanswered. frown.gif

Not unusual to get 1-2" seeing here. I also observe from Mt Laguna ~7000ft elevation (which is about 50 minutes away) where on occasions I have experienced sub arc second seeing and Mag 6.8 skies. There with seeing better than 1" my C8 shows an incredibly detailed Dumbbell nebula comparable with texture and detail reminiscent of my H-alpha shots of the nebula.

 

Even in average seeing from my backyard the 14" significantly outperformed a very good 6" APO I had. I sold that APO as it was simply too cumbersome to move and mount.

 

My personal experience suggests that there is simply no substitute for aperture in this hobby. But the reasons to acquire most scopes are driven more by personal preferences and not just objective performance criteria (which explains why I spend inordinate sums of money on premium refractors).


Edited by Astrojedi, 25 July 2018 - 04:58 PM.


#35 Sam M

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Posted 25 July 2018 - 06:19 PM

Everybody chant...

Two scope enter!  One scope leave!

TWO SCOPE ENTER!  ONE SCOPE LEAVE!

sumo.gif


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#36 noisejammer

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Posted 25 July 2018 - 06:55 PM

Ok, I'll quibble a little bit here.  For lunar/planetary imaging, the 12" will eat the Tak alive.

gaah.gif  Fair comment - and I know this to be true. But is it really imaging? :D



#37 SteelStar

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Posted 25 July 2018 - 06:58 PM

Here we go again. Every time there is a refractor vs reflector discussion, the reflector has to be bigger. And sometimes a lot bigger!  yawn.gif


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#38 CHASLX200

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Posted 25 July 2018 - 07:07 PM

Not just brighter, but far more detailed. I've had views of planets through large Newtonians, notably Mars and Jupiter, under exceptional seeing that can simply not be duplicated through any 150mm apochromat. 

 

Clear skies, Alan

No 6" APO can come close to what my 11" to 18" Zambuto and OMI Newts have done on the planets.  


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#39 CHASLX200

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Posted 25 July 2018 - 07:10 PM

Don't forget coma.

Paracorr takes care of that.



#40 starman876

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Posted 25 July 2018 - 08:37 PM

Ha. my scope is bigger than yourslol.gif



#41 gnowellsct

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Posted 25 July 2018 - 08:40 PM

Here we go again. Every time there is a refractor vs reflector discussion, the reflector has to be bigger. And sometimes a lot bigger!  yawn.gif

It can be a lot bigger (6 inch vs 14") but actually the hassle of setting up a 6 inch refractor on a GEM is probably roughly equal to the hassle of setting up a 14" dob.    

 

There's not really much interest in comparing a six inch apo to a six inch Newtonian (or SCT).   For one thing, there is a law-of-physics thing going on with illuminating the eyepiece.  Telescopes with secondaries don't get to where they need to be till about eight inches.  For another thing, we're talking two radically different engineering solutions to the problem of gathering and focusing light and engineering always takes into account cost effectiveness.  

 

So, to use a gamer term, if the Newt (or SCT) can ZERG the apo with low cost aperture, that is a different and more cost effective way to achieve the same end.

 

But as I indicated higher up if one owns a six or eight inch apo one is at a cost level where one is indulging a deeply held preference.  No discussion needed.  I'm pretty sure I max out at 130 mm.  Maybe some day if I have a windfall I'll get a TEC 140.  Six and eight inches?  Fuhgetaboutit.  I've seen them up close and know the limits of what I can do.  I've also had the opportunity to do a side by side with a couple of large apos and came away happy with my Big Tin Can.   

 

It delivers the goods.  To an extent that I had almost forgotten till my recent trip to the Adirondacks.  Holy Toledo I did not know M22 could be so fine.

 

But I think it's a very great thing that there are such fine apo apertures available to those who want to indulge.  And my own collection of refractors has taught me a good deal about what they can do and enhanced my appreciation of them.  Jeeze I even own an 81 mm.  Time was I never would have gone near one.

 

Greg N


Edited by gnowellsct, 25 July 2018 - 08:43 PM.


#42 SteelStar

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Posted 25 July 2018 - 08:57 PM

Yes, like I said, here we go again  grin.gif


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#43 starcanoe

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Posted 25 July 2018 - 09:19 PM


So one would think, well, the LARGEST refractors should have the SHORTEST focal ratios, because the mechanics of manipulating them would be much easier.   We should have f/4 or f/5 150 to 200 mm refractors.  But in reality, these scopes tend to push out on the FL: f/7, f/8, even, for TEC's 250 mm, almost f/9.  

 


 

 

What?



#44 Jeff B

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Posted 26 July 2018 - 12:25 AM

No 6" APO can come close to what my 11" to 18" Zambuto and OMI Newts have done on the planets.  

Wow.  Which planets did they do it on, what did they do, how did they get there and was it, like, legal? smile.gif


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#45 infamousnation

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Posted 26 July 2018 - 12:35 AM

Well you already have some small scopes, so might as well get a big one.

 

The 14 will blow the 6 away



#46 CHASLX200

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Posted 26 July 2018 - 05:25 AM

Wow.  Which planets did they do it on, what did they do, how did they get there and was it, like, legal? smile.gif

Jup and Sat.  That one nite with no seeing on Feb 2001. Maxed out my eyepiece barlow combo on a 14.5" Zambuto Starmaster.  Could have kept going if i had a higher power eyepiece. 



#47 gnowellsct

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Posted 26 July 2018 - 06:52 AM

Jup and Sat. That one nite with no seeing on Feb 2001. Maxed out my eyepiece barlow combo on a 14.5" Zambuto Starmaster. Could have kept going if i had a higher power eyepiece.


I get a lot of nites with no seeing. I usually stay inside.
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#48 gnowellsct

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Posted 26 July 2018 - 06:58 AM

What?


It would be nice to have an 8 inch apo that is about as long as a c8. But y'aint never going to get one, not one you'd want to use anyhow.

#49 Jon_Doh

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Posted 26 July 2018 - 09:09 AM

Paracorr takes care of that.

That's just it, dobs/reflectors are a bottomless pit.  You have to buy a Paracorr, which isn't cheap.  And then fiddle with it for different eyepieces and depending on the eyepiece and reflector you probably have to add counterweights.  Then there are the cheshires and lasers and fans you have to buy.  If you have a truss there's a shroud.  If it's a big, heavy dob, i.e. 12-14 inches you have to buy wheels to move it around.  Like I said, they're bottomless pits and not nearly the bargain they're made out to be.


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#50 dr.who

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Posted 26 July 2018 - 10:57 AM

Simple. Neither.

 

Get a CGX-L, a TOA 130, a Mewlon 250, mount them side by side, and get a StarSense to auto align for you. Then you get the best of both worlds. Refractor for wide stuff and nights where seeing sucks and reflector for the small stuff and when seeing is excellent. If the 250 blows the budget then replace it with a Celestron EdgeHD 11" with TEMPest fan's from Company 7 since they test it for you and make sure it is a good one.

 

Alternately if the mount is too big get a CGX and, again, use the StarSense to auto align for you so you can be really lazy and not have to align the scope beyond rough polar for visual use. The new firmware/software for the StarSense lets you  save multiple scope "images" so you can move it from scope to scope. 

 

In the case of the smaller mount put the TOA on it and observe with it while you run the TEMPest fans on the Celestron on a table. Then take the TOA off, put the EdgeHD on, and observe with it after about 60-90 minutes of cool down time.




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