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New Moon Telescopes 20”F/3.3 Review

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#1 ilan_shapira

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Posted 29 August 2020 - 12:22 PM

This instrument answers to all my requirements from a big dob and is mostly used during my dark site trips.While double stars and planets are not the specialty of this scope, it handles them fairly well, but requires extra good conditions - backyard usage is not optimal as atmospheric disturbances dramatically affect the views.DSOs is where this instrument excels and provides the best performance under dark skies, especially with faint galaxies.During my last dark site session, after the COVID-19 restrictions lifted, I had barely time to observe myself as others lined up to view instead.

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#2 Guydive

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Posted 31 August 2020 - 03:16 AM

Amazing telescope. got to use Ilan's NMT on few occasions. 

 

Mechanics - smooth as butter. it's unbelievable how smooth a 20" monster can be.

Optics - again, wow. Details on nebula like no other. M42 reviles so many details. faintest galaxies show clear structures.


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#3 Starman81

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Posted 31 August 2020 - 08:21 AM

Great review, well-balanced and detailed.


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#4 Stellar1

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Posted 31 August 2020 - 08:08 PM

Great scope! nebulae must be awesome in that thing, averted imagination?



#5 ilan_shapira

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Posted 01 September 2020 - 02:17 AM

Great scope! nebulae must be awesome in that thing, averted imagination?

Thanks,

No averted vision is required. Nebulae, are magnificent with this scope, so many details that previously did not exist at all.



#6 CrazyPanda

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Posted 01 September 2020 - 12:20 PM

Great review. I'm right there with you on mechanics. My 12" Lightbridge has terrible mechanics. Not just from balance, but from backlash and a bad lazy susan that squealed like a pig being murdered when it got cold out.

 

When I built my 15" I set out with the goal to make it as stiff as possible with just the right amount of friction to provide balance for my equipment without unnecessary force to move the scope (which makes dealing with backlash harder).

Nothing more frustrating than trying to track an object at high power and fighting backlash.


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#7 stargazer193857

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Posted 01 September 2020 - 05:00 PM

Backlash, what you get from too much resistance combined with a flexing structure. Yes, NMT has this area figured out.
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#8 slavicek

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Posted 01 September 2020 - 07:37 PM

I had the same problem with planets when using my 22" F/3.3 Teeter. I got much better views of planets in my 4"Tak.

a) big Dob is not "planetary" scope

b) I made aperture mask to mitigate the problem - relatively cheap solution.

 

See elsewhere here on CN for mask designs


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#9 stargazer193857

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Posted 02 September 2020 - 08:09 AM

I had the same problem with planets when using my 22" F/3.3 Teeter. I got much better views of planets in my 4"Tak.
a) big Dob is not "planetary" scope
b) I made aperture mask to mitigate the problem - relatively cheap solution.

See elsewhere here on CN for mask designs

Very informative data point.
Was this an off axis mask you tried on all 4 quadrants? Or just cutting off the edge, which might have reduced turned down edge?

If a big aperture performed worse on planets at the same magnification when aperture drastically reduced, that supports some theory about eye accommodation or even atmospheric cells.


Some claim that bigger is always at least as good as smaller, and just looks worse because it operates at higher mag, or can resolve turbulence better. They also say cooling of the big mirror is the issue. But if you tested with and without a quadrant mask on all 4 quadrants, that would refute those theories.

Edited by stargazer193857, 02 September 2020 - 08:12 AM.


#10 stargazer193857

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Posted 02 September 2020 - 08:14 AM

Thanks,
No averted vision is required. Nebulae, are magnificent with this scope, so many details that previously did not exist at all.


What aperture was your previous scope?

#11 ilan_shapira

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Posted 02 September 2020 - 02:34 PM

I had the same problem with planets when using my 22" F/3.3 Teeter. I got much better views of planets in my 4"Tak.

a) big Dob is not "planetary" scope

b) I made aperture mask to mitigate the problem - relatively cheap solution.

 

See elsewhere here on CN for mask designs

Thanks.

I totally agree on 'a', size (planets too bright, with filters) + F ration are against them.

As for the suggestion for a mask, I will check it out, its interesting.

I do however have a grab and go SCT that is perfect for the planets and has tracking - easier to view at high magnification and easier to deploy quickly.



#12 ilan_shapira

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Posted 02 September 2020 - 02:37 PM

What aperture was your previous scope?

Had a 12", but had more than one chance to observe via 14", 15" & 18"

Nothing in a 20" that didn't exist in the 18", but comparing to the 12" its a huge jump.



#13 spacedoutbob

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Posted 03 September 2020 - 08:31 AM

Very nice scope, About how much does such a instrument like yours cost?



#14 ilan_shapira

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Posted 03 September 2020 - 11:05 AM

Very nice scope, About how much does such a instrument like yours cost?

You can see the prices on New Moon Telescopes website.

Each depends on optics, extras and more


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#15 spacedoutbob

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Posted 03 September 2020 - 03:38 PM

Thank you, Bob



#16 slavicek

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Posted 03 September 2020 - 08:31 PM

Very informative data point.
Was this an off axis mask you tried on all 4 quadrants? Or just cutting off the edge, which might have reduced turned down edge?

If a big aperture performed worse on planets at the same magnification when aperture drastically reduced, that supports some theory about eye accommodation or even atmospheric cells.


Some claim that bigger is always at least as good as smaller, and just looks worse because it operates at higher mag, or can resolve turbulence better. They also say cooling of the big mirror is the issue. But if you tested with and without a quadrant mask on all 4 quadrants, that would refute those theories.

It's a single hole off axis mask. One mask has 4" diameter hole (to compare it with my 4" refractor). The other mask has 7" hole to maximize the off axes = no spikes = refractor like experience. Side by side, tested in my back yard, 4" dia mask performed as well as my refractor (at similar magnifications). So, when I travel to dark site I only bring my DOB (which is quite a lot by itself) I do not need to bring another telescope.  The 7" mask on my DOB gives me roughly F/10 which is nice for the planets.

I believe the problem with the bigger aperture is the atmospheric cells. Under ideal conditions the bigger aperture would naturally perform better. This is my experience, others may have different results.


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#17 stargazer193857

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Posted 04 September 2020 - 06:09 PM

You can see the prices on New Moon Telescopes website.
Each depends on optics, extras and more


If it is from NMT, that means the mask did not just hide a bad zone. So testing just one sector was good enough.

#18 Sagiflarius

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Posted 13 September 2020 - 02:53 PM

Thanks for a great review and very helpful comments.  I've been thinking a lot in the last few months and I now think a high-end, big aperture Dob is the right direction for me in the long run.

 

I have a Meade 8" SCT (an old one from a friend but seems fine).  I was wondering about a 16" Orion truss Dob or a Sky Watcher 16" collapsible for fixed use, but I think it makes sense to start with a cheap 12" Dob, take advantage of the portability and save up in the longer term for a serious big Dob to be installed in an observatory I plan on building at my new place in the next 18 months.

 

This has helped firm up my thinking that a big high-end Dob is my end goal. I've read a bit about masking, but I only thought of it in the sense of dealing with big aperture in turbulent seeing and had missed the idea of making a big fast dob work better with planets.  Almost like having two or more scopes in one, to suit viewing conditions and what you're viewing.



#19 George N

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Posted 14 September 2020 - 10:11 AM

Great review!

 

First: I've been an owner of an Obsession 20" F/5 for 18 years, and I've known Ryan for at least 8 years - going back to the days he was 'just' making a few scopes for good friends. Three friends own NMT Dobs - of the earlier "classic" design, but built to the same standard of perfection as the current Hybrid design. I've seen, but never observed thru the big 27" and 36" "classics" that he made in prior years. I'm a member at Kopernik Observatory & Science Center, Vestal, NY - which owns a specially commissioned 12.5" Dob by NMT designed for use by folks in a wheel chair. It is a very fine instrument.

 

I've set up next to Ryan at several star parties (CSSP, Black Forest, Stellafane) over the years and had the opportunity to use his personal telescope - pretty much identical to the one reviewed. I had already come to the same conclusions as this review! On one lazy afternoon Ryan and I played around with a laser collimator - moving the scope around to various positions, and we saw no drift in the laser position at all. At night - I saw only superb views completely comparable to my 20" F/5 with an excellent mirror.

 

The "down sides" mentioned are - to me - "normal" for a 20-inch Dob of any "brand" or ATM origin. On those few excellent seeing nights we have in the Northeast - you can't beat one - but on most nights the big Dobs are best used on faint fuzzies. I did note with Ryan's scope (one of the first Hybrids) that the movement was a little stiff compared to my Obsession 20 - something he said could be improved. Oh -- and I had to bend down to view thru the eyepiece even near the zenith - a three step up the ladder climb for my Obsession 20! I would think for a 6 footer like me, most viewing would require a stool with this scope.

 

Finally - at age 72 I'm pretty close to no longer wanting to view perched on a frosted-up ladder wearing winter gear. It is getting close to the time to pass on my excellent 20-inch F/5 to a lucky younger person who can take advantage of it for another 18 years. I am very likely to order a 20 or 22 NMT of similar design as my next 'no ladder' big Dob.


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#20 ilan_shapira

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Posted 15 September 2020 - 03:43 AM

Thanks for a great review and very helpful comments.  I've been thinking a lot in the last few months and I now think a high-end, big aperture Dob is the right direction for me in the long run.

 

I have a Meade 8" SCT (an old one from a friend but seems fine).  I was wondering about a 16" Orion truss Dob or a Sky Watcher 16" collapsible for fixed use, but I think it makes sense to start with a cheap 12" Dob, take advantage of the portability and save up in the longer term for a serious big Dob to be installed in an observatory I plan on building at my new place in the next 18 months.

 

This has helped firm up my thinking that a big high-end Dob is my end goal. I've read a bit about masking, but I only thought of it in the sense of dealing with big aperture in turbulent seeing and had missed the idea of making a big fast dob work better with planets.  Almost like having two or more scopes in one, to suit viewing conditions and what you're viewing.

Thanks!

I also have an 8" SCT as my grab and go setup and for planets and moon views - with tracking.

I did however, viewed Mars last Friday (Sep 11 2020) from a dark site in the desert. The air stabilized close to midnight and the view of the red planet through the 20" blew me away, so many details that you can actually sit down with a map of Mars and mark some items down.

But yes, when the air is less stable, these big guys tend to collect the instability as well as the light.

 

I will try the masking, it is indeed interesting option.

 

I am happy the review helped you. a 12" will do you lots and lots of good while you save for your end goal.

Clear Skies


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#21 ilan_shapira

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Posted 15 September 2020 - 07:22 AM

Great review!

 

First: I've been an owner of an Obsession 20" F/5 for 18 years, and I've known Ryan for at least 8 years - going back to the days he was 'just' making a few scopes for good friends. Three friends own NMT Dobs - of the earlier "classic" design, but built to the same standard of perfection as the current Hybrid design. I've seen, but never observed thru the big 27" and 36" "classics" that he made in prior years. I'm a member at Kopernik Observatory & Science Center, Vestal, NY - which owns a specially commissioned 12.5" Dob by NMT designed for use by folks in a wheel chair. It is a very fine instrument.

 

I've set up next to Ryan at several star parties (CSSP, Black Forest, Stellafane) over the years and had the opportunity to use his personal telescope - pretty much identical to the one reviewed. I had already come to the same conclusions as this review! On one lazy afternoon Ryan and I played around with a laser collimator - moving the scope around to various positions, and we saw no drift in the laser position at all. At night - I saw only superb views completely comparable to my 20" F/5 with an excellent mirror.

 

The "down sides" mentioned are - to me - "normal" for a 20-inch Dob of any "brand" or ATM origin. On those few excellent seeing nights we have in the Northeast - you can't beat one - but on most nights the big Dobs are best used on faint fuzzies. I did note with Ryan's scope (one of the first Hybrids) that the movement was a little stiff compared to my Obsession 20 - something he said could be improved. Oh -- and I had to bend down to view thru the eyepiece even near the zenith - a three step up the ladder climb for my Obsession 20! I would think for a 6 footer like me, most viewing would require a stool with this scope.

 

Finally - at age 72 I'm pretty close to no longer wanting to view perched on a frosted-up ladder wearing winter gear. It is getting close to the time to pass on my excellent 20-inch F/5 to a lucky younger person who can take advantage of it for another 18 years. I am very likely to order a 20 or 22 NMT of similar design as my next 'no ladder' big Dob.

I wish I could have met with Ryan to raise a toast for his excellent craftsmanship. This scope has brought me nothing but excellent observations beyond my expectations - and this Friday, Sep 11, I have been to the desert on a dark skies and had a huge fun tracking down faint galaxies in Andromeda.

As I told Sagiflarius, at midnight that night, the air was so still, and Mars was just amazing.

 

Its a full package here, optics, height & mechanics that makes this a superb instrument for DSO.

Planets I can view from home, with a smaller scope and tracking, but under dark skies - the NMT shines


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#22 JimV

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Posted 21 September 2020 - 03:16 AM

My homemade 17.5" f/4.4 has the focuser at 30 degrees rather than horizontal.  Makes for much less neck stress.  It's easier to look downwards than get on your knees and look upwards.

I don't know why Obsession, Webster, and NMT make this design mistake.


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#23 Jeff L

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Posted 21 October 2020 - 05:36 PM

Seems like an awful lot of material blocking the opening 



#24 jcastarz

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Posted 24 October 2020 - 09:57 PM

I have the baby brother to Ilan's scope:  a NMT 12.5" f4.5.  I've been very happy with it, and frequently take it up to Skyline Drive here in Virginia.

 

With respect to JimV's comment, I had Ryan place the focuser further towards the tube's top side.  But while looking down is easier on my neck, it comes with a price:  I have to engage the focuser lock screw a bit more than I'd like.

 

With respect to Ilan's special box to transport the top ring in, I too, made up a box to do this at first.  But then I had Ryan make up some mounting brackets to hold the ring in place about 7" above the mirror box using the truss frame bolts on both the mirror box and the ring.  This saves room in the car while keeping the ring rigidly mounted above the mirror box and out of harm's way.


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#25 George N

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Posted 27 October 2020 - 10:01 AM

My homemade 17.5" f/4.4 has the focuser at 30 degrees rather than horizontal.  Makes for much less neck stress.  It's easier to look downwards than get on your knees and look upwards.

I don't know why Obsession, Webster, and NMT make this design mistake.

I've sat in the grass to observe something just above the horizon -- with the UTA of my Obsession 20 just over my legs! No, I've not done it in the snow!  wink.gif

 

I'm thinking of having my next big Dob with the focuser like JimV's -- but -- I will need to go up one step with the scope above around 75 degrees altitude ( not done very often ) and I'm wondering if that will cause a problem with a little stool and the corner of the "rocker box".

 

Also -- does this position make "hand tracking" and star-drift thru the eyepiece field more confusing? I'm sure the owner would get use to it - but it could be a problem using the scope for outreach.

 

NMT will put the focuser where the customer wants. For a while at least Ryan offered an option to make the whole truss/UTA assembly rotatable. Not sure if he still does that - but it did add a little cost and additional weight.


Edited by George N, 27 October 2020 - 10:03 AM.



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