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New Moon Telescopes 20”F/3.3 Review

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New Moon Telescopes 20”F/3.3 Review


It's been just over six months of usage of the NMT 20"F/3.3 telescope and I feel it’s about time I share my experience with it.


The scope and a NMT observation chair are waiting for dark skies in the Israeli desert


I have been hooked on astronomy ever since childhood, but life always pulled me in different directions, until two years ago. At that time I got an achromatic refractor and from there the sky stopped being the limit. After that I moved to a Sky Watcher 12" Dob and quickly understood that I loved dobs, and wanted a bigger one.


How big? As big as I can handle.


Currently owned scopes:

NMT 20"F/3.3

Celestron 8" Evolution



On my future list:

A sun scope for visual use

An Apo refractor for wide field views


I have set the following requirements for a big dob:

- No need for a stool/ladder

- Fits in my car

- Secure during drive

- Secure in the field

- Easy to assemble/disassemble

- Good optics

- Collimation hold

- Last but not least - Mechanics


The option of a 20" was not on the table - I didn't know that such big and fast scopes are available to amateurs and once I did, the price was a bit of a blocker. However, doing some math (more with my heart than with my head) made me realize that compromising on an expensive instrument will only cause me regrets and eventually, I decided to buy the one I really want.


After some research and discussions with a few vendors and Ryan from NMT, I realized that this is the instrument that answers my needs.


I ordered the 20"F/3.3 with Fullum Optics Mirror, Feathertouch ultralight focuser, Secondary dew heater, Thousand oak dew controller, Telrad, mount for optical finder, wheelbarrow handles and a custom Tablet & 2” eye pieces stalk and with the selected type of woods - you get to choose which type each part is made - full customization.


Build process images were shared constantly.


The scope arrived on time.


After six months of usage I am ready to share my experience and double check how the scope answered my requirements:


No need for a stool/ladder:

The focuser in zenith is at the correct position - flat feet and no stretching the neck is required


Fits into my car:

Fits. This was known of course, but the first time I loaded it was a bit scary. The scope is not light weighted - its mirror box (with mirror included) is 61 pounds. I managed to lift it alone on a few occasions, But I prefer a pair of aluminum ramps for loading. The wheelbarrow comes with big wheels, making the process of loading easy.


Folding Loading Ramps


Secure during drive:

The mirror box is solid and there is a wooden cover to protect it, no flexible plastic covers here. Very secure


Secure in the field:

Again, the mirror is within a solid box and is well protected. There is a very small opening in the back,  but it exposes the bottom of the mirror, not its surface.


Easy to assemble/disassemble:

Assembly is a breeze. I remember attending an outreach in which a specific 18" truss scope was assembled - by 4 people. Out of the box, Assembling the NMT was easy - and it was the first time I assembled a Truss scope myself. disassembling is easy as well. The only thing that might be considered hard is loading/offloading from the car. Again, with the ramps, I can do it alone.


Collimation hold:

I did not notice a worsening in views during a full night. I tested it at the end of the night once as using a cheshire requires light. It was still collimated. Many warned that a scope that fast requires extra precise collimation. So it's a laser for rough collimation and a cheshire for the final tuning. Works like a charm.



I can't stress enough how important the mechanics are in a scope. My 12" had a slight backlash when moving, the movement was not very smooth, it had freedom that could suffer from wind (actually moved) and its balance was terrible - using ES 24mm/82 eyepiece caused it to sag when pointing below 30 degrees.


The NMT does all of this differently. First of all, although there is the option to mount counterweights, there is no need. The altitude bearings are big and provide extraordinary balance. The scope stays balanced with a Nagler 31mm + Paracorr type 2 + optical finder or without any accessory!


Horizontal movement is also smooth but with a bit firmness, preventing the scope from moving from stray wind gusts.


Replacing eyepieces leaves the scope right on target.


The combination of smoothness, firmness and no need for counterweights makes this instrument mechanically perfect.


(balanced perfectly with everything mounted on top)


Optics and View:

I am no expert in this area and my eyes are not perfect, I will share my experience with it and stuff that friends noted.


- Nebulae - The views are amazing and exceeding anything I expected. Lots and lots of details. From Orion to California, to Veil to the summer Nebulae all look fantastic. It was the first time I saw the Horse head. no need for averted imagination.


- Globular clusters - spectacular, stars can be seen very deep within them


- Open clusters - with this scope, open clusters jumped in priority for me as they are visible in their full glory. The double cluster, fitting in the field of view is just wonderful


-  Galaxies - Here comes the true power of the 20". More details than expected in the smaller galaxies, galaxies that were not there before suddenly pops out and the big ones - M51 for example - are full of details. Arms are distinguishable, details between them are clearly visible, swirls of dust and the arm that slaps NGC 5194. Viewed it with the 3-6 Nagler zoom and could discern so many details.


- Double stars - There are better scopes for splitting multiple stars. While stars are as pinpoint as possible in a F/3.3, it requires the best of conditions to view the bright ones in high magnification.


- Planets - I have mixed feelings about observing planets with this scope. The secondary mirror is huge and as such, the contrast suffers. In addition, such bright objects suffer greatly from bad atmospheric conditions. If it shakes, the image shakes. I did however manage to have one exceptionally good and stable night where the planets shone (shone and harmed my night vision) with many details visible such as Encke Gap on Saturn and On Jupiter, swirling clouds could be visible.


- Moon - Here, even with the huge central obstruction, the moon, even going to the limit of my manual tracking and atmospheric disruptions is very vivid and full of details. One can lose himself in lunar views.


Comments from friends and colleagues:

One friend indicated an astigmatism that is noticeable in high magnifications, others, not less experienced than him, viewed in x450 & x600 and did not notice any issue.


A friend with an 18" noted that he could see more details in M51, and others with many years of observation experience indicated that they had the best views using this scope.


Our astronomy club elder noted the excellent quality of the mirror, He was amazed that an F/3.3 could provide such performance.


Any one that observed through the scope noted the superb mechanics and fun of handling it.



Maybe getting the scope with a full UTA could have been better - secondary mirror more protected during drive and without a special case I ordered for it, could even take less space in the car. In addition, the Focuser position could have been placed a bit higher and not leveled with the ground which could have made viewing very low objects a bit easier (usually I don’t go that low).


- Full UTA might handle dew better?


- Removable altitude bearings can dramatically reduce the scopes footprint inside the car and is well to be considered (it would however complicate assembly/disassembly).


These issues have zero effect on my experience with the scope.


To sum things up

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.


Bottom line:

For usage under dark skies, this is the best instrument I could get for myself. You buy such a scope once and you get a device for a lifetime!

  • Mark Strollo, George N, Neptune and 28 others like this


There's something that makes the 31T5 be worth in fast scopes: one can see the whole field when using glasses or Dioptrx.

Those that have negligible astigmatism can go for a Ethos 21. Otherwise, the 100° cannot be enjoyed. Next eyepiece with a field stop close to the maximum is the 31T5. With astigmatism + Dioptrx or glasses + f/3.x it's a compromise: 31T5 for widest true field with wasted exit pupil, or a 22T4 with a smaller field. If one is lucky and astigmatism is very low the Ethos 17 without correction is another option. Next option is ES92 17 with glasses.

My NMT on order will be f/4.5 (5.15 with PC2). Perfect for 31T5 with Dioptrx. I should be able to use the Ethos 17 without it, just OK. If my astigmatism goes a bit higher, the Nagler 22 and 17 T4 are ready.

I'm glad to hear that shadow of the secondary is not disturbing with the Nagler 31 and a faster scope.

Anyway, despite astigmatism being more evident, a f/3.x class has still the huge advantage of keeping your feet on the ground. And a larger f/# won't solve the issue of largest true field possible with pin point stars at your maximum pupil. We have to live with that! (Glad that mine is mild... actually my *non* observing eye has zero! But cannot change the habit)

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