- iStar Optical’s Phantom FCL 140-6.5 review
- Who’s Afraid of a Phantom: Istar Phantom 140mm F/6.5, that is?
- SHARPSTAR 94EDPH APOCHROMATIC REFRACTOR
- My Losmandy G11T review
- FIELD TEST: THE NOH CT-20 ALT-AZ MOUNT
- SkyTee-2 Alt/Az Mount Review
- SharpStar Askar ACL200 200-mm f/4 astrographic telephoto lens
- A review of the Unistellar EVscope
- Astrotrac 360 tracking platform – first impression
- FIELD TEST: CARL ZEISS APOCHROMATIC & SHARPEST (CZAS) BINOVIEWER
- Omegon 32mm 70º SWA eyepiece review
- Review of iPolar hardware and software for polar alignment
- Review of the Hubble Optics 14 inch, f/4.6 Premium Ultra Light Dobsonian Tele...
- My experience with the Starizona Landing Pad
- A quick Review of the MIGHTY MAX 12V 100AH BATTERY
CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
FIELD TEST: THE NOH CT-20 ALT-AZ MOUNT
Discuss this article in our forums
The NoH CT-20 Alt-Az Mount
By: William A. Paolini, August 9, 2021
Fig 1: Close up of
the NoH CT-20 Alt-Az (Altitude-Azimuth) mount configured with a Vixen-style
Image Credit: Author.
[NOTE - This product evaluation was conducted in 2021].
The NoH CT-20 Alt-Az (altitude-Azimuth) mount is a product offering that is designed, manufactured, and sold by Mr. Noh in South Korea. The manufacturer's website is www.nohsmount.com. The mount is currently hand-manufactured and offered under the product name of NoH's CT-20 Mount. The marketing literature for this astronomical mount lists the following as some of its features and specifications:
Mount with a single Vixen-style saddle
Dual Saddle (comes standard with Vixen-style saddle);
150mm x 130mm x 100mm
44lbs / 20kg (maximum recommended)
4.4lb / 2kg
$650 USD (as of August 2021)
1. 7" Extension Pier accessory ($100 USD)
2. Losmandy-style saddles are also available
3. Encoders are planned to be available by end of 2021 with a step resolution of 499,712 steps for altitude and 655,360 steps for azimuth
239-3,Ssukgogae-ro, Wansan-gu, Jeonju-si,
Jeollabuk-do, 55070 South Korea
Fig 2: Vendor supplied specifications
(as of 2021).
A complete list of features and purchasing information is available from the manufacturer at www.nohsmount.com (firstname.lastname@example.org).
Fig 3: Multiple views of the NoH CT-20 Alt-Az mount head. Image Credit: Author.
1) Locking screw for the left
altitude-axis accessory mounting plate
2) Threaded holes used to mount dovetail saddle onto the left altitude-axis accessory plate
3) Bubble level
4) Left and right altitude-axis accessory mounting plates
5) Altitude-axis friction knob
6) Azimuth-axis friction knob
7) Saddle locking knobs to secure the telescope's dovetail plate to the mount
8) Screws to secure the dovetail saddle accessory to the right altitude-axis accessory plate
9) Vixen dovetail saddle accessory
10) Utility hole for leverage when tightening and loosening the mount head from the pier or tripod
The Altitude-Azimuth type of mount is my personal favorite for visual astronomical observing. I prefer this design because they tend to be lighter than other mount types since they generally do not require counterweights like equatorial mounts, eyepiece orientation stays consistent through the complete range of motion with no need to rotate the focuser, no need for polar alignment, and most importantly pointing the telescope toward a celestial object is completely natural and intuitive. Another plus for me is that Alt-Az mounts often come without any electronics for finding celestial objects nor motors for automated tracking which means for me that there is no need to bother with batteries or chords for electricity as I like keeping my observing as uncomplicated as possible. Altitude-Azimuth mounts are also in my experience the fastest mounting to setup with nothing to do other than place the mount on the ground, attach the telescope, and start observing. So for me, they are the optimum mount where the equipment never gets in the way of the observing so that vast majority of my focus can be on the sky which is where I want it to be. The NoH CT-20 mount I received for this evaluation was a completely manual version of this mount type. However, according to the manufacturer they will soon be offering encoder capability for those that enjoy automated object location and do not mind the extra burden of needing power sources and interface displays.
Fig 4: Dimensional measurements of the NoH CT-20 Alt-Az mount head.
Image Credit: Author.
Overall, upon unpacking the CT-20 mount looked and felt extremely well built. Fit and finish on all visible components was excellent. The girth and weight of the mount further conveyed the impression that it was very solid and capable. Note that my CG-5 tripod, which does not use a 3/8" bolt, already had the factory center screw removed and replaced with the more standard 3/8" threaded bolt as I have other mount heads that use the 3/8" attachment standard. Therefore, adding the optional NoH 7" Extension Pier to my Celestron CG-5 tripod was quick and easy as all I needed to do was to screw the component onto the tripod base's bolt by hand. Attaching the CT-20 Mount head to the extension pier was easy as well and simply required that I rotate the mount head onto the 3/8" threaded bolt coming out of the top of the 7" Extension Pier. To tighten the mount head firmly to the extension pier, the CT-20 has a smooth bore hole near its base (see annotation #10 in Figure 3), so I inserted an appropriately sized metal rod into the hole, I used an Allen wrench, and used that for leverage to firmly secure the mount head to the pier. Once this was completed the mount was ready for observing in the field as the Vixen-style saddle was already attached to one side of the mount head when I unpacked the mount.
With the mount now fully ready to go, I first did some daytime observing to become familiar with its operation. I first attached my TSA-102 telescope to the mount (approx. 15 lbs without eyepieces). With the CT-20's altitude-axis and azimuth-axis friction knobs engaged tightly to keep the saddle from moving (see annotation #5 & #6 in Figure 3), and the saddle locking knobs fully loosened so no longer protruding into the saddle's dovetail plate holder (see annotation #7 & #9 in Figure 3), I slid my TSA-102 with plate attached into the CT-20's saddle and tightened the locking knobs. I found the length, width, and engraved grip lines of the saddle knobs more than adequate to get a very firm lock onto the Vixen plate. Note that the altitude and azimuth-axis friction knobs, as well as the saddle locking knobs, are not captive so if you unscrew them too far they will become removed from the mount and I have found this consistent with my other alt-az mounts.
With the TSA-102 now securely attached to the mount, I loosened the altitude-axis and azimuth-axis friction knobs as well as the Takahashi clamshell knobs to loosen the telescope in its holder, and slid the TSA-102 tube in its clamshell so that it was neutrally balanced on the mount. I then tightened the telescope Takahashi clamshell knobs so the telescope was secure in its holder and began to examine the movement of the CT-20 on both of its axes. With the axes friction knobs loosened the movement of the telescope around both axes was free and smooth. I then added a little tension to both the altitude and azimuth-axis knobs and the movement of the telescope on each axis now required some force to overcome the resistance I dialed in. The movement under tension remained smooth and silky as I rotated the scope fully on round both axes. I then added a 40mm XW eyepiece to the telescope so that the altitude-axis was now out-of-balance by a little more than 1.5 pounds (0.7 kg) on the focuser side of the telescope, and strongly tightened the altitude-axis friction knob so the telescope would hold steady even though significantly out of balance. In this severe out-of-balance condition the movement of the telescope was still nicely smooth, although additional force was needed as expected to move the scope with the altitude-axis friction knob set so tightly. Overall the performance of the mount seemed excellent in this familiarization test using the TSA-102.
I next repeated the same familiarization test using the much heavier and larger APM-152 (approx. 26+ pounds or 11.8+ kilograms without eyepieces). With the APM-152 now attached to the CT-20 mount, testing it both in a balanced and unbalanced state on the mount like with the TSA-102, I found the movement of the mount in both the altitude and azimuth directions remained smooth and firm. The only point of note was that with the scope in a strong out-of-balance state, I found I was wishing the altitude-axis friction knob was a little larger so it was easier to tighten. I felt the knob was not as easy as I would have liked to grip and strongly tighten due to its relatively small 1-inch diameter. I was still however able to adequately secure the axis turning the knob with my bare hand so the scope stayed in position even though far out of balance. Note - I relayed this small point to the manufacturer and they stated that they would address it with an improvement in a future release.
Overall, the initial product inspection, attaching it onto my existing tripod, attaching my telescopes, and daytime familiarization tests demonstrated that the CT-20 continued to give the impression of a solidly engineered mount with well thought out ergonomics and smooth operation. Even with a large 6-inch f/8 refractor in the saddle, the mount seemed like even this long and somewhat heavy scope would ride very well for astronomical operation at magnification. But nighttime testing would of course be needed to confirm this impression. Suffice it to say that at this point in the process, I was pleased with what I was seeing and experiencing.
3. Field Test
Fig 5: APM/Lunt-152 f/8 ED-Apochromat (left) and TSA-102 f/8 Super Apochromat (right) telescopes with the
NoH CT-20 mount head and 7" Extension Pier on a Celestron GC-5 Tripod used for mount performance testing. Image Credit: Author.
Field testing was conducted under the heavily light polluted skies of Vienna, Virginia (Red Zone), which is located approximately 15 miles west of Washington, D.C. Outdoor temperatures during field testing typically ranged between 60-75°F (15.5-23.9°C) with humidity averaging 40-60%. Elevation of the observing site is approximately 360 feet (110 meters) above sea level. Telescope setup was on a mowed grass covered field.
Due to the nature of this test (i.e., stability and smoothness of a mount's operations), celestial object selection was not deemed critical to the testing. Therefore, a selection of stars, double stars, and the Moon were used for the tests. Mount stability tests were conducted with both nighttime celestial observing as well as daytime terrestrial observing. Motion and tracking tests were conducted only with nighttime celestial observing.
For the out-of-balance tests each telescope was balanced in the mount with the very light 1.25" 8mm RKE (approx. 2.2 oz or 62 grams), then not re-balanced when the 2" 40mm XW was used (approx 24.7 oz). This meant the telescope was out-of-balance by at least 1.4 pounds (22.5 oz or 638 grams) and heavier at the eyepiece end of the telescope. The process was also reversed balancing the scope with the heavier 40XW and not rebalancing when the 8mm RKE was used, so the telescope was then lighter at the eyepiece end by the same 1.4 pounds (22.5 oz or 638 grams). Various other less radical out-of-balance situations were also modeled using magnifications up to 600x in the APM-152 and up to 410x in the TSA-102.
Recovery tests were also conducted to determine settle time when the telescope was jarred or hit. These were done by locking the telescope on target at highest magnifications, 600x in the APM-152 and 410x in the TSA-102, then hitting the diagonal with my hand with moderate force. A stop watch was used to measure the time for the view through the eyepiece to settle back to fully stable. Note that these tests were conducted using a steel legged tripod which can accentuate vibrations and without any vibration suppression pads under the tripod.
Smoothness of operation tests were conducted with the telescopes in both in-balance and out-of-balance conditions, locating and tracking various stars and double stars as well as various features on the Moon at different magnifications, including maximum 100x/inch aperture magnifications. General observing without testing was also conducted to determine how much the mount's operation and ergonomics either facilitated or hindered the observing process.
Testing results were either recorded at the time of occurrence at the telescope using a voice recorder or annotated immediately after the test session. Each performance test was replicated multiple times to ensure consistent and accurate results were recorded. When results were compiled, there were no discrepancies or conflicting test results found between the multiple tests, otherwise those tests would have been redone until the root cause of the discrepancy was identified and eliminated.
The NoH CT-20 mount head and the NoH 7" pier extension accessory were attached to a Celestron CG-5 tripod (2"/51mm diameter steel legs) for all tests. The two telescopes used for the tests were: the Takahashi TSA-102 f/8 Super Apochromat (triplet) and the APM/Lunt-152 f/8 ED-Apochromat (doublet). The weight of TSA-102 optical tube fully configured with accessories and heaviest eyepieces exerted a load of approximately 17 lbs (7.7 kg) with an operating length of at least 35 inches (889mm). The weight of the APM/Lunt-152 f/8 ED-Apo optical tube fully configured with accessories and heaviest eyepieces exerted a load of approximately 26 lbs (11.8 kg) with an operating length of at least 51 inches (1295mm).
Fig 6: Eyepieces used for testing. Image Credit: Author.
The diagonal used on both telescopes was the 2" Baader BBHS Silver Mirror Star Diagonal. Eyepieces used were: a 40mm Pentax XW (700g/24.7oz; 30x in APM-152; 20x in TSA-102), a 10mm Pentax XW (390g/13.8oz; 120x in APM-152; 82x in TSA-102), a 7mm Pentax XW (390g/13.8oz; 171x in APM-152; 117x in TSA-102), a 5mm Pentax XW (395g/14.0oz; 240x in APM-152; 164x in TSA-102), an 8mm Edmund RKE (63g/2.2oz; 150x in APM-152; 102x in TSA-102), and a Tele Vue 2.5x Powermate (204g/7.2oz; w/5XW 600x in APM152; 410x in TSA-102).
Note - the weights shown for the configured telescope optical tube assemblies and accessories are based on manufacturer data. Actual weights were not measured.
Field testing was conducted for several months during the summer of 2021 using both a TSA-102 f/8 refractor and an APM/Lunt-152 f/8 ED refractor. The following are the testing results and impressions of the NoH CT-20 mount from those tests.
¬ Impact Recovery-Time Performance ¬
The first test I performed was to take the mount into the field, lock both axes while focused on a target at a magnification of 410-600x, and then give the diagonal a good lateral jolt with my hand to simulate the telescope being bumped. I used a stopwatch to then time how long it took the view through the eyepiece to settle to being fully still once more.
With the TSA-102 attached to the mount, the magnification set at 410x, and the scope fully balanced for the 5mm XW eyepiece with 2.5x Powermate attached, the view took just under 1 second to fully settle after I applied the impact to the side of the diagonal. This test was repeated multiple times on multiple occasions and remained consistent. I then repeated this same test, only this time the TSA-102 was set on the mount in an out-of-balance condition. For the out-of-balance setup I balanced the telescope with no eyepieces or amplifiers in the diagonal, then added the 5mm XW eyepiece with 2.5x Powermate. This meant that the setup was out-of-balance by being almost 1.3 pounds (21 ounces or 590 grams) heavier at the focuser. The altitude friction knob on the CT-20 was then tightened sufficiently so the telescope would stay pointed at any target I selected. Movement of the telescope to a variety of targets while in this condition remained positive and smooth. Giving the diagonal another lateral hit of the same magnitude as the previous test showed that the time to settle remained the same at just under 1 second. This test was also repeated multiple times on multiple occasions and remained consistent.
Next I mounted the larger and heavier APM-152 f/8 refractor onto the mount and repeated the same tests I did with the TSA-102, only this time the same eyepiece and amplifier combination used with the TSA-102 produced 600x in the APM-152. For this test, the settle time was also the same regardless if the telescope was balanced for the eyepiece and amplifier or left out of balance and heavy on the focuser end by the same 1.3 pounds. The settle time for this setup with the heavier APM-152 however was longer at 2.5 seconds (Note- the behavior of the motion while settling for both scopes was the same, with the larger motions from the impact only occurring at the very beginning and then quickly setting to smaller motions for the majority of the settle time).
After conducting these tests I felt that the result with either telescope was fully acceptable as the motions from the impact were not radical, well controlled, and when the view settled to fully still the telescope remained precisely on-target (excepting of course for any celestial object drift that occurred during the settle time -- this fact was further confirmed using daytime tests on stationary targets).
¬ In-Balance Performance ¬
When testing the CT-20's performance with the telescopes in a properly balanced condition, I chose to conduct these tests with the telescopes set at more extreme magnifications so even he very smallest issues would be readily apparent. I therefore used magnifications of approximately 50x per inch of aperture or 600x with the APM-152 and 410x with the TSA-102. The eyepiece I used for these magnifications was the 5mm XW with a Tele Vue 2.5x Powermate. This combination yielded an effect focal length of the eyepiece-amplifier combination of 2mm. At these extreme magnifications observing would also be more comfortable given the larger 70-degree AFOV of the XWs and their very comfortable long eye relief.
Fig 7: "Artist's View of the Polaris System". The primary component of the Polaris multiple star system is a rare yellow supergiant star. Yellow supergiants comprise less than 1% of all cataloged stars and only exist in their yellow supergiant stage for an extremely brief few thousand years of their lifetimes! Polaris is about 430 light years distant, approximately 40x as large as our Sun and almost 1300x as luminous. Credit: NASA, ESA, G. Bacon (STScI).
Since both telescopes were in-balance with these eyepieces for this test, I kept the altitude-axis and azimuth-axis friction knobs of the CT-20 mount fully loosened so the telescopes would smoothly move with virtually no friction. With the TSA-102 I observed several stars and double stars, ending the observations with a good look at the double star Polaris. While this double is not considered by many to be anything noteworthy, I find it a very intriguing observation. The reason for this has nothing to do with the aesthetics or grandeur of the view through the eyepiece, although the subtle yellow color of Polaris can be quite beautiful at high magnification, but the observation becomes very intriguing when understanding exactly what is being observed. Polaris is a yellow supergiant star, and this stage of a star's life is extremely short and therefore rarely seen in the galaxy -- yellow supergiants comprise less than 1% of all cataloged stars as the yellow supergiant stage typically lasts only a scant few thousand years. So for me, I enjoy lingering long when observing this particular double star so I can fully appreciate the rarity of this rare object I am observing.
Fig 8: Lunar
crater Clavius. During some of the testing this crater was prominently placed
on the Moon
and was a stunning visual at 600x in the APM-152 refractor. Image Credit: NASA/LROC.
Moving on to the APM-152 at 600x magnification, I primarily spent the observing sessions for this test on the Moon. My first impression was to be taken aback at how free and effortless it was observing the Moon at this extreme magnification with this large telescope fully balanced on the CT-20 mount. The CT-20 provided incredibly smooth and effortless movement as I moved across the surface of the Moon at magnifications high enough that I felt more like I was hiking on the Moon instead of observing it from afar! Since I more often am using my telescopes in an out-of-balance condition with the altitude-axis tension knob engaged with a good amount of friction, I am just not used to this state where there is no tension and virtually no friction on the scope. As a result, I was able to make extremely small and precise movements across the lunar surface and was also able to easily track the Moon even though at 600x as only the gentlest of force was needed to move the scope in time with the Moon as it coursed through the night sky. Needless to say I spent a very long time observing the Moon for this test and fully enjoyed every moment of it. In-balance performance of the CT-20 using either the TSA-102 or the APM-152 at high magnification I felt was nothing short of spectacular!
¬ Out-of-Balance Performance ¬
While many observers judiciously re-balance their telescopes when they switch between different accessories such as eyepieces, I tend to be lazy in this respect and instead depend on adding tension on the altitude-axis so that the telescope stays where I point it even though sometimes in an extreme out-of-balance state. Of course, re-balancing the telescope as you change accessories is the best approach, but for my personal preferences I needed to ensure that a mount can still perform smoothly and effectively and without being choppy in its movements even when significant tension is applied to the altitude-axis tension knob as I tend to not re-balance.
For a typical observing session I will use a small cadre of eyepieces, usually one 2-inch eyepiece and then several 1.25-inch eyepieces in both wide-field 70-degree apparent field of views (AFOV) and smaller 50-degree class AFOVs. In my case, on a typical general observing session I usually take a 40mm XW, 10mm XW, 7mm XW, 5mm XW, then several small format 50-degree AFOV eyepieces such as Edmund RKEs or Takahashi LEs. More often I will take out the Edmund RKEs as I prefer how single coated optics render planetary details and double star colors. With these eyepieces, their weights range from 25 ounces (700 grams) for the 40mm XW at the heaviest and then as light at about 2.2 ounces (62 grams). So given that range of eyepieces, the weights will vary from 2.2 ounces (62 grams) to 24.7 ounces (700 grams). If one then balances the scope for the weight in the middle of that range, or 13.5 ounces (383 grams), then the scope will only be out-of-balance by a maximum of +/- 11.5 ounces (326 grams), depending on which eyepiece is chosen. This is in my opinion the optimum approach if one does not intend to re-balance the telescope with every eyepiece change.
For my testing however, I decided to stress the mount more and therefore balanced the telescope with either the lightest or heaviest eyepiece to see how it would handle more of a maximum out-of-balance situation, taking note if movement remains smooth, if there was any greater initial force needed to start movement, and if there was any backlash when movement was stopped. The reason I decided to accomplish this test using the maximum weight differential of the eyepieces I brought into the field was again because I tend to be lazy and want to start observing as soon as possible. That being the case it is easier to simply balance the telescope for the first eyepiece I will be using, which will most times be the larger and heavier 2-inch eyepiece that provides the widest true field of view (TFOV).
When a telescope is out-of-balance on its mount I find that backlash is typically the most common issue one encounters. This issue, if it occurs, generally will affect only the altitude-axis. What you will see in the eyepiece when there is backlash is that when you move the telescope to center a celestial object in the field, when you stop the movement the telescope will then settle in one direction or the other depending on if the eyepiece-end of the telescope is lighter or heavier than the balanced state. If the eyepiece-end is heavier, then when moving the telescope's eyepiece end upward to view an object that is lower in altitude, once you release the telescope gravity will cause the heavier end of the telescope to sometimes move downward some before it comes to a full stop. If the eyepiece-end of the telescope is lighter than the balanced state, then the situation will be reversed.
With the TSA-102 balanced for the 40mm XW eyepiece in the CT-20 mount, I then replaced that eyepiece with an 8mm RKE so the telescope was now lighter at the eyepiece-end and out-of-balance by 1.4 pounds (22.5 ounces or 638 grams). I then had to apply a significant amount of force on the altitude-axis knob of the CT-20 to keep the telescope steady when moved in this severe out-of-balance situation. Movement of the telescope from horizon to zenith and all around the azimuth-axis remained smooth even though the altitude friction knob was tightly set. Initiating movement of the telescope from the resting position also showed no need for any extra force being needed to get the movement started. Finally, with the eyepiece-end of the telescope being out-of-balance by the significant 1.4 pounds (22.5 ounces or 638 grams), a small amount of backlash was then detected when raising the eyepiece-end of the telescope to point the telescope at a target lower on the horizon. Looking through the 8mm RKE eyepiece (102x) I measured the backlash that occurred to be approximately 1.8 arcminutes. I considered this excellent performance for an out-of-balance condition this large as even in the smaller AFOV of the RKE eyepiece (approx. 50-degrees), at 102x in the TSA-102 the AFOV of this eyepiece showed slightly less than 1/2 degree or 30 arcminutes. Therefore a backlash movement of 1.8 arcminutes compared to an AFOV of almost 30 arcminutes meant that when I centered the object in the AFOV, the backlash shift was only about 1/17th of the size of the AFOV; so very minimal.
Repeating the same test using the larger and heavier APM-152 refractor showed no difference in outcomes and the backlash shift when the scope was out-of-balance by 1.4 pounds (22.5 ounces or 638 grams) at the eyepiece-end was the same 1.8 arcminutes. However, in the APM-152 the 8mm RKE produced 150x magnification which in turn meant the true field of view it displayed was a smaller 1/3 of a degree or 20 arcminutes. The 1.8 arcminute backlash therefore showed as being more significant and 1/11th of the AFOV, which for my observing habit and preferences I judged to still be quite acceptable.
Having the CT-20 mount handle an out-of-balance condition of 1.4 pounds (22.5 ounces or 638 grams) at the eyepiece end of the telescope is in my estimation significantly unbalanced. So I decided to also examine at what out-of-balance weights no backlash occurred. To do this I balanced the scope without any eyepieces in the diagonal then proceeded to add eyepieces of different weights noting when I first could see noticeable backlash. Using this approach I determined that noticeable backlash did not occur until the eyepiece weight exceeded 10.6 ounces (301 grams). This meant that if I balanced the telescope at the mid-point weight of the eyepieces I took into the field, instead of balancing for the heaviest (40 XW) or lightest (8mm RKE) that I would have likely not encountered any backlash as balancing at the mid-point of those eyepieces would have resulted in a maximum out-of-balance condition of only 11.5 ounces (326 grams), very close to the 10.6 ounces (301 grams) where no backlash was observed in testing.
4. Summary Impressions
Fig 9: APM 152-ED f/8 refractor with the NoH CT-20 mount head and 7" Extension Pier
on a Celestron GC-5 Tripod. Image Credit: Author.
After several weeks of field use of the NoH CT-20 mount for general astronomical observing with both my TSA-102 and APM-152 refractors, I found the operation and use of this mount to be highly intuitive in the field. The axis friction knobs are conveniently located and are tactile-distinctive from the saddle plate knobs that hold the telescope on the mount, so there was never any question in the dark as to which knob-type I was operating. Operation of the mount was also smooth and precise throughout the testing and general field observing sessions. At no time did I ever find that the CT-20 mount was anything but superlatively capable to handle even my large 6-inch f/8 refractor.
I also found it quite satisfying that the mount maintained very smooth and precise pointing and motions even when the telescope attached to it was kept in a very significant out-of-balance state, showing no backlash when out-of-balance by almost seven-tenths of a pound at the eyepiece end of the telescope (10.6 ounces or 301 grams), and acceptable backlash even when that out-of-balance condition was more than twice as large at a full 1.4 pounds (22.5 ounces or 638 grams). With the CT-20 I was therefore able to effortlessly focus on my observing without the mount hindering that pursuit in any way. I actually felt the CT-20 facilitated my observing by providing such a steady and precise visual platform for my telescopes. And when I used the mount with a telescope balanced for magnifications as high as 600x, I discovered a world new-to-me as the motions were so buttery-smooth and precise that the telescope required nothing more than the gentlest of touches to point it at new objects or even track objects at these extreme magnifications. My high power lunar observing when using the NoH CT-20 actually provided me with a more satisfying and memorable time with the Moon than I've had in many years! Given that the CT-20 Alt-Az mount also has the ability to hold two telescopes side-by-side, easily handles larger weighty telescopes, and will soon have an ecoder option for those needing automated support for finding celestial objects, I would characterize the CT-20 as a nice example of a very good and fully capable top-tier alt-az mount that one can grow into as they acquire larger refrative telescopes. Overall I found the NoH CT-20 an outstanding alt-az mount and actually the first alt-az mount I have used without slow motion controls that felt does not need those type of controls. Very highly recommend!
~ ¬ ~
About the Author
William "Bill" Paolini has been actively involved in
optics and amateur astronomy for more than 50 years, is author of the desk
reference on astronomical eyepieces: Choosing and Using Astronomical
Eyepieces which is part of the Patrick Moore Practical Astronomy Series
published by Springer of New York, has published numerous product reviews on
major online amateur astronomy boards, and has worked as a tour guide volunteer
for the United States Naval Observatory's historic 1873 26" and 12"
Alvan Graham Clark refractors.
Bill has been observing as an amateur astronomer since the mid-1960's, grinding
mirrors for homemade Newtonian telescopes during the 1970's and eventually
owning, using, and testing over 400 eyepieces in a wide variety of telescopes
including Achromatic Refractive, Apochromatic Refractive, Newtonian,
Maksutov-Cassegrain, and Schmidt-Cassegrain optical designs. Today he enjoys lunar,
planetary, and doubles star observing from his suburban home 15 miles west of
Washington, D.C. and at a darker site in rural Virginia about 45 minutes west
of his home where he focuses on open cluster, globular cluster, nebula, supernova
remnant, and galaxy observing.
This article is placed into the Public Domain by William Paolini 2021; Author images © William Paolini 2021.
For permission to use author images separate from the full article, submit your request to email@example.com.
- skypilgrim, Jaimo!, george tatsis and 7 others like this