When it comes to astronomy and astrophotography, the mount pointing the telescope is as important as the optics.
This article is based on the L500 mount from Planewave Instruments. There are three mounts in the series. Except for the size, they all look and operate the same, and have unique features compared to the conventional German Equatorial mounts.
The smallest of the Planewave series is the L350, which is a good choice for telescopes up to 14 inches. L500 is the mid-sized version, with the range topping out with the L600 for telescopes up to 24 inches. The table below summarizes the weights and prices:
|L350||110lbs (50kg)||100lbs (45kg)||$11,500|
|L500||257lbs (117kg)||200lbs (91kg)||$20,500|
|L600||338lbs (153kg)||300lbs (136kg)||$33,500|
While most mounts use motors and gears to track the movement of the sky, the L-mount has no gears at all. Each axis has a direct drive motor that consists of a series of coils and permanent magnets that move the mount using a magnetic field – thus, no physical contact. There is an encoder on each axis that controls the precise movement. This avoids the periodic error often caused by imperfections in meshed gears, and no backlash or need for lubrication and periodic maintenance.
The caveat is that there are no gears, so the drive isn’t “locked” in place when deenergized. This means if the telescope is not perfectly balanced, it will “flop” down into the hard stops (spring loaded). Also, I suspect it may be a bit more sensitive to gusts of wind, but these mounts are usually in observatories that are well protected.
Performance is where the L500 mount really excels. The first thing that struck me was how fast it can swing a large telescope across the sky. While 5 degrees per second is considered fast, the L500 could do 10 times more, at 50 degrees per second. That could be used to track fast objects like asteroids or satellites with ease.
It is also highly accurate. Planewave specifies that the mount is capable of a pointing accuracy of less than 10 arc-seconds, and a tracking accuracy less than 0.3 arcseconds over 5 minutes, allowing unguided imaging, if needed.
Furthermore, the mount is completely silent. All I hear is the internal PC sized fan running. It’s nice to avoid annoying neighbors at 3 a.m.!
The payload capacity of the mount is average. The L500 mount is rated at 200 lbs (91 kg), which isn’t that much considering it weighs 257 lbs (117 kg) and is about the size of a small person. For reference, the conventional Astro-Physics AP1600 mount is a lot more compact and weighs less than half as much, with 10 percent more payload capacity. However, the AP1600 does require counterweights – unlike the L500.
The L500 is designed as an observatory mount and can be used in both Alt-Az and equatorial modes. The former is easier to set up and takes up less space, but a field de-rotator is needed when not operating as an equatorial mount. Most long exposure imagers will work better with an equatorial setup (aligned with the earth rotational axis), as such a setup usually tracks better and has fewer problems with differential spikes and flat-frame calibration.
In equatorial mode, the user would have to order a wedge specific to the latitude. They come in 5-degree latitude ranges and are quite pricey at $3,500. Here, even better balance is required by adjusting the left-right position at the base of the mount and the fore-aft position of the telescope on the saddle. There is also an optional “Ascend” balance accessory, which I highly recommend, for $380.
Perhaps one of the L500’s most welcomed features is that it does not need to “flip” the telescope at the meridian. This has a host of benefits such as saving time, not moving off target, and avoiding possible collimation and focus issues due to flex.
An added bonus is the ability to attach a second telescope on the other side of the fork. I have a short focal length refractor dual-mounted.
Except for the help needed to lift the mount (it can be disassembled in two pieces), I was able to set the mount up myself after going through the detailed manual. It requires AC main power – it will handle anything from 90 to 264 volts – and a single USB cable or ethernet to operate. There is plenty of space to run cables through the mount, with several access panels, which is a big plus for safety.
Planewave includes its PWI4 software free of charge. The software has ASCOM drivers to connect to your favorite imaging or planetarium software. It also has a basic planetarium and database to search for targets. There’s even a wireless joystick for manual control.
PWI4 is very straightforward to understand and follow. Once set up, I had to run the “Auto tuner” that tunes and calibrates the motors; this takes from 15 minutes to about an hour depending on the settings.
The mount isn’t fussy with polar alignment in Alt-Az mode, but it needs a sky model to point and track accurately in either mode (which requires about 30 points to get started). There is a polar align tool for equatorial mode. Model building is mostly autonomous, but can only be done with Maxim DL, which is not included. I did find that a bit disappointing, and it’s about $500 for that. Both the tuning and model building are required only once unless you change the setup.
One point to note is that the mount only has incremental encoders. Unlike absolute encoders, it doesn’t know if it’s been moved when powered off. The user needs to “home” the mount before operation; otherwise, it can get lost.
The L-Series mount hardware and software are very straightforward. The fast speed and lack of meridian flip make them more efficient. Setting up isn’t too complicated, and the manuals and videos are very helpful; so is Planewave, if you give them a call.
Performance is excellent, and I would say it is a very good choice for those who do not require their setup to be portable.
Besides the cost, the main limiting factor is that the mount takes up quite a lot of space and needs a larger unobstructed area to operate in equatorial mode compared with conventional mounts. There is a calculator from Planewave, though, to work out the area needed.
See video of the L500 mount in action: https://youtube.com/shorts/rfqWWxE77CY?feature=share