DocTelescope LaserMax II 20” F/3.6 review

DocTelescope LaserMax II 20” F/3.6 review / Jonathan Zion Mozes

I've been waiting a long time to write this review; finally, it is here! This will be the first of (at least) two posts reviewing my new DocTelescope Lasermax II 20" telescope. The first post will focus on the design and construction process and my first impressions after receiving it and taking it for a first light session in my dark site. The second post will focus on the scope's push-to and go-to capabilities, provided by a Nexus DSC Pro system and the brand-new Nexus StarDrive system (also by Astro Devices).

Preliminary note: while I have been (and still am) in close contact with both Marco Guidi (DocTelescope) and Serge Antonov (Astro Devices) throughout this process, this is my independent review, without any affiliation to either of them, other than my appreciation for these artisans' exquisite work and their friendship. Also, I've already published a similar (but not identical) review in Andromeda, the Israeli Amateur Astronomy Forum, and you are welcome to view it at this link (in Hebrew).

The Beginning

I've been watching the night sky since I was little and have had a telescope since I was 13, when my parents bought me a 4" Meade SCT. I still remember the nights I spent on my childhood house's roof and the awe I felt looking through its eyepiece at the different phases of the moon, at Saturn or Jupiter, or the joy of seeing comet Hale-Bopp's core up close. When I moved out of my parents' house, the scope stayed there for storage, and (I guess as is the case with many other amateur astronomers) stayed there (except for sporadic excursions) until 2020 and the COVID-inflicted self-isolation. Telescope technologies have made quite a lot of progress in the two decades that have passed, and I was soon the proud owner of a new 9.25" Celestron Evolution motorized telescope. I also started looking for friends with whom I could share my love and passion. I found them in the Andromeda Astronomy Forum, whose members have ever since been an integral part of my monthly observation sessions in dark sites across Israel. As my understanding and appreciation of the night sky increased, so has my arsenal of scopes and accessories, with a 4" Astro-Tech refractor (102ED) joining the fray and a plethora of eyepieces and astrophotography equipment.

In the summer of 2022, about six months before my 40th birthday, I decided it was time to take the plunge and become a "half meter man," and so have begun to research my needs and desires of a dream scope that will serve me for years to come (and can also be considered my mid-life crisis). This months-long process led me to decide on a 20" Dobsonian with a (relatively) thin and fast mirror, and I commissioned the mirror from Optiques Fullum. As for the structure, the two finalists were Ryan Goodson at New Moon Telescopes and Marco Guidi at DocTelescope. Both had excellent reputations, although Ryan was by far more well-known. Ultimately, I decided to go with Marco for two main reasons: first, I thoroughly loved the design of his scopes, with a clean and "Italian" line made entirely of stainless steel and industrial-grade aluminum, compared with NMT's wood and carbon fiber. Both telescopes are roughly the same weight and are in the same price range (given Optiques Fullum as a primary; DocTelescope also works with other manufacturers, such as the Italian Zen Optics or Fausto Giacometti, and choosing those would have lowered the price of the scope). Both manufacturers appeared at that preliminary stage to be very communicative and responsive, and both were already in talks with Astro Devices regarding its next-gen drive (at the time, the future of ServoCat was still uncertain). The second reason was an issue of chemistry and connection – despite a language barrier (my control of Italian leaves quite a lot to be desired, and Marco's English is not perfect either), I found in Marco a kindred spirit, and I felt my dream telescope would be in excellent hands, or as Marco said to me – "I treat all of my telescopes as if they were my children." Two minor points that also tipped the balance in favor of Marco was his design choice for mirror support: Marco uses an 18-point + whippletree edge support, while Ryan uses a cable sling on linear bearings; I preferred having the former over the latter. And finally, an extra perk was that visiting Marco near Venice, Italy (see pictures), during the design and manufacturing process, seemed (at the time) much more feasible than visiting Ryan in the US.

In the picture: Me and Marco (on left) with a scope he just finished building, February 2023.

At this stage, I still haven't decided whether I'll go for a fully motorized scope or a push-to option: my normal usage is primarily manual, using either star-hopping (with the ingenious StarHopper app) or StarSense Explorer as my push-to guides. However, I felt that having a motorized scope would come in handy in some of my use cases:

1. When using higher magnification eyepieces.
2. When conducting community outreach.
3. Doing (mainly planetary) astrophotography.

I decided I wanted a motorized system, but only if its existence would not prevent a smooth manual operation. Having tested a ServoCat installation in which the tension cable caused the manual operation to be more rigid, I decided to wait for the new Nexus StarDrive to be available, as it was supposed to employ a slip-clutch mechanism that would allow simultaneous manual and automatic uses. 

Another consideration was what f-ratio to use. Given my height (1.85m, or roughly 6'1"), I could choose an f/3.3 or an f/3.6 mirror and still have two feet on the ground when the scope points to the Zenith. All things being equal, I decided to go with the 'slower' mirror, whose collimation might be easier. In hindsight, I should have gone with the f/3.3, as later design choices have led to me being 2cm short of comfortably using the scope at Zenith. This is a minor inconvenience, but still, there you have it.

The mirror was ready in November 2022, with Normand Fullum delivering it to Marco a few weeks ahead of schedule. It is a beauty of a mirror, with top-notch knife edge test results, as you can see below. It is paired with a 4.5" Antares secondary mirror with a PV value of 1/20.

In the pictures: (1) The mirror during its production phase; (2) After finishing the coating process; (3) Surface analysis and knife edge test results; (4) Star test simulation

Initially, the scope was scheduled to be completed by the summer of 2023, with the hope that Serge would have finished developing his new drive system by then. Life, however, got in the way, and as I was accepted into a degree program in the US for a year, I asked Marco to postpone production by a year. This decision was also favorable for the Nexus drive, as it was only available for installation in the summer of 2024. To make a long story short, after quite a few intercontinental video calls (with Serge being in Australia, Marco in Italy, and me in America), I received my scope in August 2024 – the first in the world with the new Nexus StarDrive system!

In the pictures: (1) The proud a happy owner of a new 20” Dobsonian; (2) First assembly

Initial impressions

Honestly (or as honest as a proud owner can be)? What a fantastic scope. The longer wait and anticipation have only intensified the joy of finally having and using it.

Here are its final specifications:

• 20" F/3.6 primary mirror by Optiques Fullum
• 4.5" minor axis secondary mirror by Antares
• Feathertouch focuser
• One vixen bracket on the secondary cage
• Wheelbarrow handles on the rocker box
• A custom eyepiece and nexus/tablet stalk
• An extra scope saddle on the mirror box to 'piggyback' my AT72EDII
• Weight and measurements:

• Rockerbox - ~ 19 kg, 66x66x23cm

• Mirrorbox - ~ 15 kg, 61x75x58cm (height includes altitude bearings)

• Mirror - ~ 16kg, 20" (508mm) diameter, 1.5" thick

• Secondary cage - ~5 kg, 65cm diameter, 34cm high

• Trusses - ~ 3kg, 140cm long

• Total - ~57 kg

• The mirrorbox comes with a large and silent ThermalTake fan to cool the primary mirror (12v DC plug)
• Includes a shroud for the trusses and a dew cover for the secondary cage 

After assembling it for the first time, it was immediately apparent that all the parts are of exceptionally high quality and are made almost exclusively of aluminum or high-grade industrial stainless steel, so there is no fear of it gathering rust due to dew or humidity. 

The telescope feels very stable, and after several practice sessions of assembly and disassembly, setting it up takes about twenty minutes. As I mentioned earlier, mirror support is provided by 18 points connected to each other through a central hub. Two sturdy whippletree (whiffletree) holders provide edge support with two rollers on each one.

In the picture: The Rockerbox and Mirrorbox, with mirror support mechanism visible

All parts were machined and polished to perfection, save one – the eyepiece stalk itself has two holes through which it is connected to the rockerbox. One of these holes seems to have been too tight, so it was hard to fit into place. A short use of a drill widened it, and it now fits into place easily. Other than that – it is simply exquisite manufacturing. 

One design choice that I was surprised with was that of the collimation screws for the secondary mirror. While the primary mirror has three large collimation screws beneath it (with very easy-to-turn thick knobs), the secondary has three pairs of hex screws (requiring the use of an Allen wrench). According to Marco, collimation of the secondary mirror is rarely needed, as it keeps its relative position to the primary between uses, even if the scope is stored in parts between observation sessions. While I was skeptical about this claim, it has proven valid until now. I've assembled the scope four times, one of which was in a dark site after a three-hour drive, and I still did not need to collimate the secondary mirror. I am impressed.

In the picture: The Antares Optics secondary mirror and its collimation mechanism

As for the Nexus StarDrive system, its review will wait for another time. While the hardware is already installed on my scope (two NEMA-17 stepper motors with harmonic gearboxes connected to the main StarDrive controller, which is in turn connected to the Nexus DSC), the firmware is still in the works, and I should be receiving it in the next couple of weeks. In the meantime, the scope is entirely manual, equipped with Astro Devices' 311,296 steps magnetic encoders for a flawless push-to experience. As I said above, one of the innovations of the StarDrive system is its use of slip clutches to allow both manual and motorized use simultaneously. There are two red clutch knobs (one for each axis) that allow the user to control the level of friction and the amount of force needed to make the scope move. Getting the setting right takes a bit of experimenting, but once it's there, the scope moves smoothly and is very well balanced, even when using a Paracorr and a heavy eyepiece such as the Ethos 21mm. I will say that when I attached the AT72 to its dovetail, the scope became a bit bottom-heavy, and preventing it from moving down the altitude axis required strengthening the clutch to a point in which I needed to use more power (pushing with at least three fingers) to make the telescope move. One more thing about the clutches – it is the azimuth clutch knob that caused the scope's height to increase by 2 cm, as Marco needed to raise the rockerbox off the ground to accommodate the knob.

In the pictures: (1) Alt clutch; (2) Az clutch

First Light

I finally tested the scope out in the field a few days ago, having taken it to a Bortle 3 dark site in southern Israel. It fit nicely inside my car with the back seats folded, and in the future, I can even make it have a smaller footprint, as I took both the secondary cage and the primary mirror in separate wooden boxes. Settling in and assembling the scope was an absolute pleasure, taking just under 30 minutes this first time outside my house (You can see a timelapse video of the aseembly process here). I did run into a little problem at this point, as the azimuth clutch knob got caught in the mat I placed over the ground – I did not experience this behavior at home since I have hard floors, while the sand of the desert is soft, and so the scope's legs sunk into the sand (not to give anyone a heart attack – the scope was on a mat that sunk as well. There was no direct contact between the sand and the scope J). The solution was raising the legs a bit with wooden planks. Collimation was a breeze, and as I said, only the primary mirror needed to be collimated. I conducted a quick star test and found lovely, round, bright Airy Disks on both sides of the focus, with little change when pointing to stars towards the horizon (~20 degrees above the horizon) or towards the Zenith (to be fair, I performed the test about an hour after astronomical darkness, so there still were some apparent atmospheric disturbances as well as some temperature differences between the mirror and its environment).

In the pictures: (1) My loaded car ready to go stargazing; (2) The scope assembled and ready to go

Mechanics – the scope behaved very similarly to my controlled environment at home. Its movement was smooth in both axes, with the only difference being that I needed to strengthen the azimuth clutch a bit to mitigate the strong winds that characteristically blow during the first few hours of twilight and night in the desert. I only needed to strengthen the altitude axis clutch when I used a considerably lighter eyepiece, such as the Nagler 3-6mm planetary zoom. In all use cases, vibrations were kept to a minimum and have not been a source for anguish or frustration throughout the night.

Optics – I don't have much to compare this mirror to, as the only other 20" telescope I know has a similar mirror made by Optiques Fullum. However, I can say that the views were magnificent for every object I targeted that night, be it a nebula, a galaxy, a globular cluster, or plain old stars. I could discern so many suns in M13, even in the core, and higher magnifications (~x350, using 6mm) were still bright and kept a round shape with no noticeable (or significant) astigmatism. I was in awe of the details I could see in galaxies, large (M31) or smaller (NGC6946). Nebulas had real depth to them, with filters (The Western Veil (NGC6960), using OIII) and without (I just got lost in the thick soup that is the Orion Nebula (M42)). Smaller objects, such as the Ring Nebula (M57) or the Blue Snowball Nebula (NGC7662), were beautiful and more colorful than I remember viewing using smaller apertures. The night was even good for viewing the planets in large magnifications, although I had to use ND filters due to the brightness of Saturn and Jupiter. Still, I managed to see the Cassini Division even at the current angle of the rings and discerned cloud layers on both planets. Throughout the night, other observers came, and the number of "oooos" and "ahhhhs" I heard raised a smile of contentment on my face.

Quirks and Improvements – The single most significant issue I have with the scope is that I need to stand on the tip of my toes to view objects at the Zenith. I really wanted to avoid this, but I decided that, in the end, I prefer having the drive system over this. Time will tell if I made the right decision J

Another minor issue is the eyepiece holder: while it holds five eyepieces, only one has a 2" diameter. I would have preferred having at least one if not two, more 2" holders. This is, of course, fixable, and I might just drill a wider hole for one more eyepiece. And finally, I am still learning how I want to store the scope and the mirror. Currently, the primary is stored in a separate wooden box, but I believe that if I can find a suitable cover, I would like to store it inside the mirror box. I'll probably post an update regarding this later.

Temporary summary

As of the time writing this review, while I'm still waiting to enable the motorized capabilities of my scope, it has exceeded all my expectations (except the Zenith viewing one). It is truly a work of art, a beautiful design that is also highly functional, and I am grateful to all of the professionals who made this dream come true. I also appreciate the human connections I formed during this scope's inception and hope that I enjoy it and my new friendships for years to come.

Stay tuned for part II of the review in a few weeks or so.