Go to or not go to
I have two regular observing sites and so I have two equatorial mounts. They are both of the SkyWatcher HEQ5 type but one is the basic model while the other is the "Pro" version with "go to" capability. I am therefore in a position to make a comparison between the two.
I use both with either a 254mm aperture Newtonian telescope plus DSLR camera or with the camera alone on the mount. I use the equipment almost exclusively for imaging, because that reveals far more than can be seen visually. I use my eyes only for finding my targets, using my Hopper application on a laptop while viewing through a wide 40mm eyepiece. (Hopper is downloadable from the Programs tab of the BAA Computing Section web site at britastro.org/computing.)
I have been using the basic HEQ5 for more than 7 years but the "Pro" version was obtained last year (2013). I wanted two mounts so I could stop transporting one mount between two locations. My reason for obtaining the "Pro" model was that I thought I might start using a guiding system but in reality I have not yet taken that step. I very quickly found that I preferred the old mount and my several reasons for that should become clear from the following table.
Firstly I would note that the tripod is the same for both models. It is quite substantial but portable, especially if you separate the motorised head from it. The legs are easily extendable. At first sight the tripod may seem wobbly but the key is to really tighten the eyepiece holder rack so it braces against all three legs. Then the tripod is very rigid and vibration-proof. The tightening has to be done after polar alignment and that can make the alignment/tightening process rather iterative (tightening may affect the alignment).
|Basic HEQ5||HEQ5 Pro|
|Motors & controllability||Direct drive. Not suitable for controllers. Silent.
(I have read on the web that newer versions have stepper motors, but there seems to be confusion about this. Perhaps someone else can clarify.)
|Stepper motors. Necessary for control from PC. Some say these motors cause vibrations but I have not noticed this. They can be heard however.|
|Power supply||Runs happily for months on 8 D-type batteries. A battery holder and cable were provided. This makes for great portability.
A mains power supply can of course be used if required.
|Much greater power needed, so it has to be from the mains or one of those big rechargeable power packs. This makes the mount less portable for me.|
|Drives at power on?||Yes - immediately drives at sidereal rate, which is what I always want for deep sky, asteroid and comet photography.||No - you have to go through the start-up procedure (below) and then go down into the menu system to switch driving on. I find this extremely irritating. But you do have a choice of sidereal, lunar or solar rates.|
|GO TO ability?||No||Yes, with thousands of objects stored in the hand controller.|
|Hand controller||Simple illuminated buttons for 4 drive directions. Switches: on/off and N/S hemisphere.||Many buttons for settings and control. It is easy to press the wrong button in the dark and get very confused. The illumination of the buttons only comes on when you have pressed one, and only stays on for a minute or so.
The controller is inevitably complicated to enable the GO TO capability.
|Polar alignment||Sighting scope with useful graticule in RA axis, plus setting circles. There are fine adjustment screws on both axes.
Beware if wearing spectacles: the eyepiece end of the sighting scope has sharp edges that can scratch your lenses (expensive).
|Exactly the same as for the basic model.|
|Start-up procecedure||Switch the power on. Could not be simpler.||Multiple steps. If you don't need the "go to" facility you can just press the ENTER key about 10 times to skip through, but after that you do have go into the set-up menu to start driving. For alignment on the stars you can select 2- or 3-star methods. You then have to know the "common" names of the bright stars (not Bayer letters or Flamsteed numbers). If you are in a dome it is particularly awkward because of continually having to move the dome slit.|
|Slewing||The motors cannot be driven at a faster rate. I keep the friction clutches just tight enough that I can easily slew by hand.||The motors have 9 speed settings when driven by the keypad on the controller, the fastest of which is a reasonable slewing rate.
As I never do the start-up alignment procedure I find it simpler to use the slipping clutch method as on the basic mount. But this must not be done if you wish to keep the star alignment and "go to" capability.
|Meridian flip||No||I did not know about this until after I bought the mount. If you have gone through the star alignment procedure the mount flips the telescope through 180 degrees when it reaches the meridian, to avoid the scope tube hitting the tripod legs. Will it be accurate enough for a photographic sequence to continue? I have not risked it. In any case this is a flipping nuisance in a dome because the telescope would no longer be looking through the slit afterwards. I consider this another reason for NOT doing the star alignment at start-up.|
|Parking||Not applicable.||The controller enables you to park the telescope at the end of a session so that the star alignment procedure should be unnecessary the next time power is switched on. Unfortunately the parked position has the telescope pointing upwards, making it impossible to lift it safely off the cradle to take it indoors. (I leave the mount in the observatory but not the telescope, because of dampness/dew.)|
|Periodic gear error correction training?||No||Yes, the manual describes a procedure for recording the errors so they are corrected at "run time". I have not tried it.|
I believe the "go to" capability was introduced on equatorial mounts with the aim of making it easier for beginners to find celestial objects. However, the complexities described above negate that advantage, in my opinion.
Surprisingly I have found the "Pro" mount less accurate in its supposed sidereal driving rate. In taking long sequences of images I have found that the field drifts (after averaging the periodic gear errors) by 24 arcminutes per hour.This results in a significant offset in a 1-minute exposure (ie, significantly greater than the star image radius caused by atmospheric turbulence). My basic mount has no such drift though of course both mounts do have periodic errors, which the photographic method has to take into account. It is almost as if the "Pro" mount requires a guiding system rather than merely making it possible to use one. I have queried this with the suppliers but got no explanation.
In the 1970s the software guru Edsger Dijkstra wrote a famous paper, published under the title "GOTO statement considered harmful" (because the GOTO statement in BASIC and other programming languages encouraged bad program structure). Whilst I would not go as far as saying that "GO TO" mounts are harmful, I cannot see that they help anyone, given the complexity of setting up and using them. Give me the basic mount any day! But I realise this may be controversial...