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Visual Only: 150mm Triplet APO vs 14" Dobsonian

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#101 JMW

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Posted 28 July 2018 - 01:42 PM

My wife and I observe together and enjoy going to the Golden State and Oregon star parties. We setup a Webster D14 with f/4.3 Zambuto Mirror and ServoCAT-Nexus DSC with a TEC 140 on a DM6 and Planet tripod. I think this is a perfect combination. The TEC 140 is usually acclimated faster than the Webster and we start out the evening looking at the bright planets at dusk through the TEC 140. Once it is dark the Webster is ready. The TEC 140 is favored by my wife for its ease of use on the DM6 mount. We enjoy the bright DSOs, planets, double stars and wide field of view objects such as Veil or North America nebulas. It is also large enough to detect galaxy clusters. We enjoy the Webster for detecting the dimmer stuff or making the medium dim stuff brighter. 

 

The machined DM6 and wider field of the refractor means we can alway land the eyepiece on the target with the Nexus DSC. Sometimes I have to hunt a little bit more or drop down to a wide field eyepiece when find targets in the Webster using the Nexus DSC. Both have 40K encoders. We use both with Sky Safari linked via wifi to the Nexus DSC on each setup. If I am going to really push magnifications on a night with excellent seeing, I will engage the ServoCAT so we can have tracking a 300+ powers.

 

I prefer viewing wider fields of view and double stars on the TEC 140. If we are only out for a shorter period or don't have as much room we just bring the TEC 140. If the sky is partly cloudy and the viewing time may be limited we stick with the TEC 140. We always bring both to star parties and enjoy comparing the views in each scope. I also like to setup our Lunt 100m 45 degree APO ED binoculars on a FTX tripod with Nexus DSC. It is fun using Panoptic 24mm in the Lunts and just cruising the dark skies.

 

So our opinion is it shouldn't be 14 inch dob vs 150mm refractor but both side by side shared with a friend or family.


Edited by JMW, 29 July 2018 - 12:09 AM.

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#102 jag32

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Posted 28 July 2018 - 02:04 PM

Because of significant issues i've read about regarding the Obsession UC line of telescopes, i'm passing on them.


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#103 gnowellsct

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Posted 28 July 2018 - 02:33 PM

 

 

So our opinion is it shouldn't be 14 inch dob vs 150mm refractor but both side by side shared with a friends or family.

I concur, but with the proviso that refractor dudes gotta have their large apos and so if they want that they should be encouraged to do so.  Looking at my own herd I've got four apos from 3" to 5" and am in line for two more.  Ain't nothing wrong with apos or refractors in general.  If I wanted a 6" TEC I would already have one.  If  I sold off a lot of the herd, not just the refractors, I could certainly put a TEC 180 on the ol' AP900 push-to.    I'm certainly hoping I have it together AT LEAST to sell one of the four inch apos if the 92s come in  (I got on the AP 92 list, while it was still open, took about two seconds to figure out that was never going to happen, and got in line for a CFF).  

 

It's just not where I want to go and one would think the five inchers would have lured me to still larger apo aperture (I sold an FS128) if I was lure-able.  

 

But me aint everybody and the people out there who want to go gadzooks in the large apo direction certainly aren't hurting anyone and almost all of them are happy with the choice. Furthermore their presence on the field at star parties adds class and diversity.  The same goes true for the wide variety of apertures in the Dob/Newt class.  

 

Greg N


Edited by gnowellsct, 28 July 2018 - 02:36 PM.


#104 Erik Bakker

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Posted 28 July 2018 - 02:34 PM

My 2 cents:

 

Scope performance under the stars is about many things. Amongst them aperture and quality of the optics. But also pride of ownership and ease of set-up and use. And the postion you observe in. Side by side on very good nights, the big quality dob will show more on anything that fits it's field of view. My custom 16" f/5 Matthias Wirth leaves me mesmerized at times with it's glorious views. No scope has ever shown me Jupiter better. My refractors always impress me with how fast they can deliver quality views. One night, I wanted to show a good friend of mine the beauty of a GRS and shadow transit on Jupiter. Even after 2 hours, the dob delivered views that were not quite sharp. But bright. My small FS102 delivered breathtaking views, soon, even under so-so conditions. Clearly showing the GRS and shady in transit. But dimmish. The dob was just.... bright that night. And needs a standing observer most of the time. A TOA150 is a different animal. Requiring more lugging to set up than a good 15"dob. Cools quicker, but nowhere near as quick as an FS102 doublet. Offers more comfort for prolonged medium-high power observing. Yet will never reach the astonishing level of detail a good 15" dob delivers. But quite easily allows photography of the sun and moon if the occasion rises. Or a Venus transit or bright comet appearing for that matter. So no simple answer to your question. But for me: the TOA150 on EM400. Or better yet, a used FS152 NSV on EM200.


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#105 gnowellsct

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Posted 28 July 2018 - 02:42 PM

 A TOA150 is a different animal. Requiring more lugging to set up than a good 15"dob. Cools quicker, but nowhere near as quick as an FS102 doublet. Offers more comfort for prolonged medium-high power observing. Yet will never reach the astonishing level of detail a good 15" dob delivers. But quite easily allows photography of the sun and moon if the occasion rises. Or a Venus transit or bright comet appearing for that matter. So no simple answer to your question. But for me: the TOA150 on EM400.

My personal view is that once you get to the level of the large dob with tracking and go to you're reaching a set-up lug and hassle that's pretty similar to a 6 inch apo or a C11/C14.   That's what I've seen anyhow.  Install and connect trusses on both ends.   Power supply needs to be hooked up, the altitude wire needs to be connected (for some reason that was pretty difficult), then the collimation routine, then initialize the computer--it was a production.  If it's shorter then setting up a refractor on a GEM it's not by much.  Adding functionality to telescope rigs tends to add setup time as well.

 

Greg N


Edited by gnowellsct, 28 July 2018 - 02:42 PM.

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#106 junomike

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Posted 28 July 2018 - 05:58 PM

Because of significant issues i've read about regarding the Obsession UC line of telescopes, i'm passing on them.

Can you PM me links to these issues as I'm considering a larger Obsession UC.



#107 Erik Bakker

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Posted 29 July 2018 - 03:30 AM

Perhaps this can be of help Mike. Just take it from there. Lot's of info, both positive and negative.



#108 junomike

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Posted 29 July 2018 - 08:18 AM

Perhaps this can be of help Mike. Just take it from there. Lot's of info, both positive and negative.

Thanks Erik, I'll give it a read (I don't frequent the Reflector Forum very often).



#109 gnowellsct

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Posted 29 July 2018 - 09:11 AM

Incidentally I recommended purchase of an 18 inch obsession UL for my club. It's a great scope. But if you think buying one of these guys is problem free you got another think coming. The paramount MX for the local outreach observatory also has teething teething issues.

#110 janapier

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Posted 17 February 2019 - 05:07 PM

On Thursday, through sheer luck, I was able to buy a custom 21" Dob from Timm Klose, a quite renowned German ATM. The mirror is hand-ground and less than one inch thick. The entire instrument weighs less than 60 lbs, mirror included. It is mechanically sound and can be assembled (as well as disassembled) in 5 min. It is an f4 lowrider - no ladders needed. Yesterday, I set it up in my yard, in the light of 3 sodium vapor lamps and without stray light protection. I trained it on the moon and observed Gassendi and Vallis Schroeteri. Seeing was quite lousy, Pickering 5 or so. For some time, I was unable to focus properly. The image got sharper, then less sharp again without passing through the point of good focus. But as the mirror cooled, and it cooled fast because of its low thickness, the best focus image became sharper and sharper. Finally, after like 1 h, it reached a level that simply cannot be duplicated by any frac within the reach of the average amateur astronomer. It was somehow irritating to look at because of the seeing, but all the details were there. I saw all the rilles in Gassendi like in the high resolution images from the books. I saw Rimae Prinz below Schroter's Valley - they were actually obvious. The position of all these super-fine lines jumped back and forth, so as to almost give the impression of double pictures. But they were rendered in a harsh way, nothing mushy about them at all. I used magnifications of up to 388x (cyclops mode). The Dob was on an EQ platform.

 

Afterwards, I took the Dob down and set up my Esprit 150ED, complete with Baader Mk. V bino and looked at the same stuff. The seeing may have had worsened a bit. Anyway, the image was in less motion than in the Dob, but Rimae Prinz were just gone, except for glimpses of the largest hooked Rille originating at the Vera crater. In Gassendi, almost all the fine structure on the crater floor was gone as well. The super-sharp frac images suddenly did not appear quite so super-sharp with the memory of the images from the 21 inch mirror fresh in my mind. It is really amazing to see what kind of resolution a 21" scope has to offer - highly recommended.


Edited by janapier, 17 February 2019 - 05:09 PM.


#111 25585

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Posted 17 February 2019 - 05:23 PM

14 inch Dob for deep sky. TOA 130 for a refractor, and grab & go.



#112 CHASLX200

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Posted 17 February 2019 - 05:52 PM

For planets a 14.5" Dob would destroy any 150mm APO on planets in my super seeing as long as it is a top notch mirror.  I can use over 1000x in the Dob vs 600x on the APO.



#113 Eddgie

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Posted 18 February 2019 - 09:15 AM

Even my mass market 12" dob easily showed more on pretty much every target that would fit into the field than my 6" Astro-Physics triplet would.

 

I will say that if seeing perfect double star splits is high on one's list, it is difficult to beat a large refractor, and of course you can get a slightly larger true field, but this comes at a huge costs both in terms of money and effort.  

Here is my 6" on a mount that I would say is a good compliment to a 6" triplet:

 

C8 and 152a.jpg

 

Yeah, if you want to have your 6" Apo be as solid at high power as a 12" dob, you gotta put it on a hefty mount.   This mount could hold this scope reasonably still at 200x, but it was four trips out the door to get it into action.

 

By comparison, my 12" dob is kept outside in the corner of my covered patio, and goes out in one trip and I can be observing in less than 90 seconds. 

 

To the OP, I would say the 14" is going to be far more competent on a far greater range of targets.   I know this because my 12" is far more competent on a wider range of targets than my 6" triplet was. 

 

Of course these days, I would rater use my Comet Catcher with my Mod 3 Night Vision eyepiece than most other scopes.  Way easier to move around and WOW! the stuff I can see!!!


Edited by Eddgie, 18 February 2019 - 09:16 AM.

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#114 rcg

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Posted 18 February 2019 - 08:27 PM

What about our changing technology? A short FL refractor and a night vision ocular for DSOs and then you only have to deal with your most often useful planetary size. And what about the possibility of color magnifying night vision … perhaps on the horizon?



#115 donadani

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Posted 19 February 2019 - 12:47 AM

I sold my perfect 14" Dob simply because it got no use… 99 of 100 times I look for planets or doublestars just from my balcony - a refraktor on a alt/az or sometimes eq mount is MUCH easier to use here because it has no limitations by the balustrade that the Dob had. My 12" and 8" Dob was better here.

 

Next problem is the use of a good (and so heavy) ADC with a Dob that is trimmed for lightwight… - no problem here with a refraktor.

 

On a starmeeting last summer I went with a 7" apo and stood directly next to a very good 12" Dob and we looked for Saturn and Mars - the Dob needed muuuuuch more longer to cool down so that it startetd to show a quiet view of Saturn - but the 7" apo with ADC definately had the edge for all the evening.

 

Sold my 8" and 12" Dobs too before some years an really never ever looked back. 

 

And not to forget that horrible spikes from the Newton spiders on bright objekts and the much more convienient views through a apo on eq mount - no really never look back. 

 

Well were the Dob was undoubtly better was on faint deep-sky objekts - no question here! - but these are not the objekts I normaly go for.

 

So finally all comes down to your own seeing habbits, your sourrounding and your prefered objects to look at to choose the right scope for YOU.

 

cs

Chris


Edited by donadani, 19 February 2019 - 12:51 AM.


#116 janapier

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Posted 19 February 2019 - 01:23 AM

What ADC are you using that is so heavy?

#117 bobhen

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Posted 19 February 2019 - 11:16 AM

With today’s technology refractor lovers can have their cake and eat it too.

 

Inexpensive video cameras and short exposure CCD cameras and (the more expensive) Image Intensifiers can all show detail in deep sky objects that no “unassisted” Dobsonian can, and in a matter of seconds or, as in the case of the Image Intensifier, in real-time. You can even use a non-tracking mount with an Image Intensifier.

 

You will give up the absolute pristine eyepiece view of the unassisted Dobsonian but in vast majority of cases you will actually see more (a lot more) detail in those faint fuzzies, and right from your light-polluted backyard without the need for traveling to a dark sky location.

 

So, “if” you are willing to add some tech to that refractor you can enjoy all the refractor attributes (thermal stability, high contrast, wide fields, high power, sitting, using tracking or push-to mounts, etc.) AND go extremely deep as well, and right from your backyard.

 

I used to have a 15” Dobsonian and now I use a Tak 120 on an alt/az mount with an Image Intensifier. Never saw the Horsehead with the 15” but with the Tak 120 and the Intensifier the Horsehead is easy and routine! No contest, I’ll take the TOA 150 on a Discmount DM-6 mount with an Image Intensifier over any size Dobsonian.

 

Bob


Edited by bobhen, 19 February 2019 - 11:17 AM.

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#118 donadani

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Posted 19 February 2019 - 12:23 PM

Hi Bob - wow, yes that intensifier-thing is one to try for me in the future for sure! Could you give us an example or link of an good intensifier for that use?

 

cs

Chris



#119 bobhen

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Posted 19 February 2019 - 12:30 PM

Hi Bob - wow, yes that intensifier-thing is one to try for me in the future for sure! Could you give us an example or link of an good intensifier for that use?

 

cs

Chris

HERE is a website with lots of good info about Night Vision and Image Intensifiers for astronomy.

 

The EAA forum here on CN is also filled with good info.

 

Bob


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#120 gnowellsct

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Posted 19 February 2019 - 01:35 PM

One of the advantages of the refractor which in years past I didn't think was "really an issue" is light scatter on aluminized surfaces.  As it turns out even humongo earth based telescopes hit a wall in terms of faintness of magnitude detection due to light scatter.  I think the effective limit is 28th magnitude (saw a presentation at NEAF).   The Dragonfly array can, even though a much smaller aperture "taken as a whole," can image down to 31st magnitude because light scatter is so well controlled.  That's why it excels at faint object detection.

 

I'm a little skeptical that the problem of aluminum light scatter matters in visual amateur observing.  I think net discussions have a tendency to take a small theoretical difference and blow it way out of proportion.   Nonetheless a bunch of Canon photographic lenses wired together can image 2.5^3 or 15x deeper than say the observatories in Chile or Mauna Kea and that says something.

 

Greg N




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