15 kilograms of steel – and we speak only about a tripod with legs almost 3 inches in diameter. Then another 15 kilograms of metal and electronics – it is a mount head alone. To make it all work we need a 2.5 kg counterweight bar and two counterweights of 10 kg each. And on top of this, you can put 35 kilograms of telescopes. In total, over 85 kilograms of astronomical happiness.
This is how the Sky-Watcher CQ-350 Pro looks in a nutshell, and thanks to the Delta-Optical company I had an opportunity to test this device. CQ-350 fills the gap between EQ6 class mounts with a 15-20kg payload capacity and the EQ8 mount with a load capacity of 50kg. For CQ-350 Sky Watcher selected the currently popular “center balanced” construction type, and thanks to that mount head weight is kept under control. This 15 kg, although it sounds serious, is the same number as for EQ6 or NEQ6 mounts. It is a sweet weight that we are able to put on the tripod ourselves, and then add our telescope.
And what is inside?
Both axes are powered with stepper motors via a toothed belt and worm gear. The RA axis has a 308 teeth worm wheel with a 155mm diameter. Dec axis worm wheel has 288 teeth. RA resolution is 0.023 arc second. The mount requires an 11-16V DC power supply with current capability 5A. Everyday work is comfortable due to the home sensors in both axes, so the mount is able to find starting position automatically. We can start that process from the SynScan pilot and SynScan application, but also from the popular GS Server driver.
Astrophotography amateurs will be pleased with PPEC – according to the manufacturer, the permanent periodic error correction curve stored in the mount has a resolution of 200 steps.
If your astro imaging setup cable management makes you nervous, you will be happy with the cables and receptacles present in the mount. There are a bunch of cables inside the head so that you may transfer DC power, USB connection, or RJ cables through the mount. One connectors’ set is placed under the dovetail saddle, and another is in front of the mount head.
There is no polar scope out of the box – if you need it, you will have to purchase it separately. But precise polar alignment is available from the SynScan hand control or SynScan app after 2 or 3-star alignment is done. There are also more and more applications that do plate-solving based polar alignment that is very accurate and fast (like SharpCap or Ekos).
Setting up the mount is not very complicated and does not take long. The tripod has a built-in level. The mounting plate is flat and has pads made with hard and slippery plastic. Placing the mount on the tripod is straightforward. Then we use four bolts – two for fixing the mount to the tripod, and another two for fixing the counterweight rod. The rod can be set in two different positions depending on the geographic latitude of our location. Then we put the counterweights, connect the power, attach the telescope and we may start the observations. Dovetail saddle accepts both Vixen and Losmandy dovetails, and we have two solid knobs to lock the dovetail.
Altitude and azimuth regulation knobs are comfortable, and after the adjustments, it is recommended to lock the mount head position with corresponding locking screws. Clutch levers have locking nuts. At the beginning I thought that was a redundant feature, but when I realized what can be the effect of accidental clutch releasing a setup with the 35kg telescope, I started to appreciate this additional solution.
But life is not perfect, and there are a few things that I did not like much.
One of these is putting all the electronic sockets to the mount head front – at the same side as the counterweight rod is present. In the “center balanced” construction the cables need to be present in the moving mount head part – we cannot change it. But all these receptacles could be placed on the rear part of the mount head, where the cables would be a less problem to manage. Currently, they are rotating at a significant radius together with the mount head, and additionally, counterweight rod presence in that area requires some attention from the user when leading the cables.
But the amount of available connections through the mount is sufficient. At the front mount head panel we have a regular DC power socket, a USB socket to control the mount, and RJ ports for auto-guiding and hand control. SNAP socket is the last input available – to control the DSLR shutter. At the panel side, there are receptacles connected with their equivalents in the panel under the dovetail saddle. There is a 6-24V power input split into three outputs. The same voltage powers the active USB 3.0 hub with four output ports. Additionally, there are three RJ sockets – 4, 6, and 8 pins that we can use for our purposes. Having that many options we can easily plan and make all the cable connections within the astrophotography setup.
The first power up went smoothly. The SynScan hand controller asked a few typical questions about location, date, time, time zone, and daylight saving time. Then it proposed finding a home position that I had accepted, and after a few moments of buzzing the mount stopped at the home position. The next question was more problematic – it was about “DEC offset”. I suspected what it was about, but checked in the manual. When we want to use a dual dovetail saddle, some of them require rotating the DEC axis by 90 degrees, because the optical axes of the telescopes are perpendicular to the main dovetail. There is however a problem with DEC axis mechanical stops. The DEC axis cannot be rotated freely 360 degrees around, because there are cables present inside the mount head. Mechanical stops were placed at the DEC axis, so it can be rotated only in a range of about 150 degrees in both directions. That is why we cannot use a dual dovetail saddle that requires a 90-degree offset of the DEC axis because the movement in one of the directions will be limited to 60 degrees only. Another direction movement can be up to 240 degrees, but that does not help. So if we want to use a dual saddle dovetail in CQ-350, we need to look for the models, where the telescopes’ axes are parallel to the main dovetail. That is why in my opinion “DEC offset” option should be disabled in this mount model.
After this reflection, I selected “DEC offset” to zero, and then the hand controller proposed star alignment to 1, 2 or 3 stars. After 2 or 3 stars alignment there is an additional option available for precise polar alignment.
I have also tested controlling the mount with a USB cable and GS Server driver. After selecting the serial port and setting the speed to 115200 bps GS Server started talking to CQ-350 and was able to control the mount.
Stepper motors in the mount head are not very quiet but work mannerly. Acceleration is smooth – does not change in a jumpy way.
Due to the presence of stubborn clouds, I have ended my first of Sky-Watcher CQ-350 Pro tests at this point. Now we wait for some clear skies during the night.
Some time passed and the weather agreed with my free time for two evenings when I was able to perform some tests under the night sky and collect data using CQ-350 Pro. The Moon was already pretty bright, so there were not many targets to choose from. The Auriga center with Flame and Tadpoles nebulae was the first captured object – via hydrogen alpha narrowband filter of course.
But before that happened I estimated the periodic error of the mount. Due to the large ratio of the main RA axis worm gear, the worm rotation period is only 280 seconds, and the periodic error measured by Guiding Assistant in PHD2 is +-3 arc seconds, which is quite a good value.
Average tracking error (for both axes) during this session is 0.76”, and it can be read from the correction analysis graph, that the largest components of that error are the ones with period 280s (that comes from the worm), but there are also corrections with period 400s – that may come out from the gear ratio of the toothed belt gear box in RA axis.
When we analyze the full log of that session we may spot the fact that corrections are not quite random, but they are periodic. It is very probable that this kind of error could be limited with the PPEC curve recorded to the mount. Unfortunately I was not able to record that. Starting it with the SynScan hand controller option did not do anything, and both the SynScan app and GS Server driver show PPEC Training option is not available. Maybe it is only the question of the software and newer version will fix that issue. Such a low periodic error with a gentle slope should be significantly fixed with PPEC.
The guiding calibration in PHD2 went perfectly, and the Guiding Assistant results are shown below.
The mount was polar aligned with SharpCap software with the error below 0.1 arc minute. The results achieved (periodic error and drift in RA) are very good, and also DEC axis backlash is low and should not be a problem during guiding and dithering.
Another captured target was a Medusa nebula in Gemini – also with a hydrogen alpha narrowband filter. This time 50 subframes were collected, each one 3 minutes long.
Despite the bright Moon I decided to record some luminance during the next night’s session. I pointed the telescope to M81 and M82 galaxies and captured 20 frames by 2 minutes of the data. Here is how it looks after stacking (it is enlarged part of the full frame):
Tracking accuracy during that session was similar – in the range 0.7-0.8”. There was a moments when it was better – around 0.5”, like in the screenshot below:
Several components are included in that total tracking error. There are mechanic errors that come from the actual mount, but also atmospheric seeing affects the guiding results. Conditions during both sessions were mixed, and seeing varied. I expect that during the good seeing periods when the atmosphere is stable, the mount will be able to achieve that 0.5” accuracy for a longer period. Additionally, the PPEC option, once available, should improve that result. Let us hope it will be fixed soon.
After these two nights, the weather said “no” again. I would like to test the mount a bit more under better conditions because after these sessions I have the impression it may perform better than I estimated. But at that point, I have the results as they are, and the numbers don’t lie. One may ask – if 0.7” tracking error is a lot? First of all, we need to remember that error does not come not only from the mount. The measured star position error also adds to the guiding error. When your guiding scope provides the star images of diameter 10-15 arc seconds, you cannot expect that scope will guide the CQ-350 mount accurately. During my test sessions, I used both Evoguide 50ED and the main refractor and the results were similar, so I assumed that guide scope parameters were good enough.
Another thing is the climate and seeing. Here in Poland, the star size is about 2.5” for most of the nights. Guiding at 0.7” accuracy will not be a problem, because the total star diameter is not just a simple sum of tracking error and angular star diameter, but it is (more less) the square root of the sum of squares of all errors.
All the sessions with CQ-350 Pro passed quickly, and now it is the time to say goodbye to the mount and also regenerate my back because setting it all up in the garden for all available pieces of the clear sky was a bit of a fatiguing process.
What did I like in CQ350?
- reasonable mount head weight for a 35 kg payload limit
- good mechanics for adjusting the head to a celestial pole
- RA and DEC axes clutch lockers
- cable management inside the mount together with an active USB 30 hub
- massive tripod
- small periodic error
- good tracking (but can be better)
What did I like less in CQ350?
- input sockets mounted in the mount head from the counterweight rod side
- some software problems (DEC offset option that should be used for CQ350, PPEC training option not available)
- wide tripod legs with “center balanced” head type may cause some problems when pointing the telescope around the zenith – telescope’s rear part may hit the tripod legs.
