GoTo FAQ?

[Cosmic Geoff]

Apologies if this suggestion is out of place, but we regularly get posts from GoTo users complaining that their mount will not perform. The answers tend to be the same, so it seems to me that a 'sticky' FAQ here or in Mount Discussion might be useful.

The usual fixes for failure to align are:

The inputs: 

Time, Daylight Saving Time (DST off in winter)

Time zone: (0 for the UK, otherwise check the timezone map in your manual or elsewhere. ) e.g. France +1, Los Angeles -8

Latitude and Longitude: to get started, enter the nearest city. For greater accuracy, look up the site position on the Internet, etc and get it in a degrees and minutes format with E or W.  Make sure you enter it in the correct format.  (And remember to change it if you travel to an observing site.)

 The Power:

Don't rely on the internal AA primary batteries used in some mounts - they discharge quickly. Use an external +12v power supply. There are various options ranging from vehicle 'cigarette lighter' outlet, mains power pack, proprietary 'power tank', DIY battery tank, etc. A 7AH battery will suffice to run the mount in most cases (but not accessories as well).

Beware the power plug - any bad contact WILL cause problems. The plug can be fettled for better contact, but also use a strain relief stuck to the mount and run the cable through it, to avoid the plug being tugged as the mount moves around.  Celestron SLT and Se mounts use a 5.5/2.1mm plug.  If you are worried about the cable winding up as the mount moves, either set 'cordwrap' (which can result in annoying 355 degree turns) or keep an eye on it and be ready to shift the battery.

Keep the battery well charged.

Aligning: (features and terminology may vary)

The tripod comes (generally) with a bubble level, and it's not there for ornament, so use it when you set up the tripod. Particularly important for one-star and Solar System align.

There are various modes - the quickest and simplest are the One Star and the Solar System align. These are good enough to get you started, or if you just wanted to look at Venus or some other planet.  Auto Two Star and Two Star are more accurate. SkyAlign uses three stars, and unlike with the other modes, you don't need to know what they are - just pick three bright stars on the sky.  The three-star SkyAlign is likely to be the most accurate, as well as being aimed at newbies. Unfortunately, newbies will find the 3-star align the most trying, especially when it terminates in a baffling 'Failure' message. 

Note that the handset may prompt you on what alignment star to use, but you can use your common sense in selecting another. Alignment stars should be well apart (~90 degrees) or close to an area you want to observe in. The basic 'Red Dot' finder is the easiest to use for coarse aligning on the alignment stars. Once started, complete the alignment quickly, centering each star in the LP eyepiece field.

There is generally some feature to fine-tune the alignment after completion (e.g. Sync or Precise GoTo), but this seems to work only on stars in the alignment star or other list, not any random object.  Likewise, there are instructions on how to perform the alignment in the eyepiece to minimize the effect of mechanical play in the gearing ('backlash').  

How accurate is it?

That seems to depend on a number of factors.  If all goes well, objects should land within the field of the LP eyepiece.  Tracking is generally very good, with people reporting that these mounts will track for hours.

Which Mount?

They fall into two classes, alt-azimuth and equatorial.  The former are usually bundled with a telescope and accessories but can be got separately in some cases. If you have no interest in astro-photography, you should choose an alt-azimuth mount as these are more compact and easier to use. If you are definitely interested in astro-photography, get an equatorial GoTo, following the advice of those who are experts in this subject.

Note that the smaller Goto alt-azimuth mounts (e.g. Celestron SLT) are made with travel in mind (i.e. stiffness is not a priority.)

Comments are welcome .

 

[alanjgreen]

Good start Geoff.

i would add that once you have started the alignment procedure then time is of the essence, if you dordle then alignment failure is likely.

i would also state that use of a red dot finder vastly simplifies the point and centre activity. The magnifying optical finders are a hinderance you can do without.

you could state that the more alignment stars you pick then the greater the accuracy will be, but with the caveat that you will need good "point and centre" skills - which is why most people only use one star which ain't very accurate over anything than a short session and anywhere that isn't near the star you picked.

 

[xtreemchaos]

great imfo mate, ive had goto for donkeys of years and never used it, I have the HEQ5 at the moment with the latest syscan, I think I might give it a go, you have made it sound so simple, the doc you get with the mount don't tell it as good.  thanks charl.

[alanjgreen]

Geoff,

maybe a few tips on eyepiece and centering?

eyepiece - I would recommend you use your main eyepiece that you intend to view with (as not all eyepieces centre on the same position) rather than a specific high power one. If you defocus the eyepiece so a star becomes a big football, then it is easy to get in centered rather than try to get a small dot into the centre.

goto direction - it is recommended while moving a star to the centre to finish the movement by going UP AND RIGHT. This helps remove backlash from the gears of the scope and helps keep goto more accurate.

[happy-kat]

Alignment stars should be selected based on the type of mount you have, it is not the same for eq and altaz. 

Nothing beats read the manual.

[happy-kat]

If you have a tablet or phone use android synscaninit application to get the right data input.

[Cosmic Geoff]

1 hour ago, alanjgreen said:

goto direction - it is recommended while moving a star to the centre to finish the movement by going UP AND RIGHT. This helps remove backlash from the gears of the scope and helps keep goto more accurate.

I'd respectfully disagree with this point. The final movement for aligning on the alignment star should conform with the final movement performed by the GoTo. However the final movement direction of the latter can be changed in the handset, and users might want to do this depending on the telescope being front-heavy or tail-heavy. Diagonals reverse the apparent sideways direction, and the movement buttons can produce a different result depending on the slew rate selected - and this feature can also be modified in the handset settings. 

All this is a recipe for confusion, and users should be aware of these issues when striving to improve accuracy.

1 hour ago, alanjgreen said:

eyepiece - I would recommend you use your main eyepiece that you intend to view with (as not all eyepieces centre on the same position) rather than a specific high power one. If you defocus the eyepiece so a star becomes a big football, then it is easy to get in centered rather than try to get a small dot into the centre.

Users may find this helpful. I normally align and do most observing with a 25mm eyepiece. 

[2STAR]

On 30/01/2017 at 11:28, Cosmic Geoff said:

I'd respectfully disagree with this point. The final movement for aligning on the alignment star should conform with the final movement performed by the GoTo. However the final movement direction of the latter can be changed in the handset, and users might want to do this depending on the telescope being front-heavy or tail-heavy. Diagonals reverse the apparent sideways direction, and the movement buttons can produce a different result depending on the slew rate selected - and this feature can also be modified in the handset settings. 

All this is a recipe for confusion, and users should be aware of these issues when striving to improve accuracy.

Users may find this helpful. I normally align and do most observing with a 25mm eyepiece. 

Good advice and also here is a Quote from some chat I had with Michael Swanson.

When selecting stars for alignment, avoid stars above 70 degrees in altitude or below 20 degrees.  Then select two stars with a separation of between 90 and 135 degrees.  Polaris is a good selection for your location as long as you are not using the scope on a wedge.  When centering the stars in the eyepiece, your current GoTo Approach settings dictate that final motions must be with the RIGHT and UP arrow buttons in order to eliminate the effects of gear backlash.

[Geoff Lister]

I use the Stellarium planetarium program to select the bright stars. By advancing time, at dusk, Stellarium adds the names of the stars as they would become visible to the naked eye. By doing the same, for the middle of each month of the year, I have produced a table of 24 stars, and for each month, identified the best 3, 4, or 5, and their direction (N, NW, W etc.), giving good azimuth and altitude separation, and avoiding local trees, fences and buildings.

I use Synscan "Brightest Star" alignment, so I only need to see the first star to do a manual slew to its location. The handset suggests the second star, and this is where the list helps me from choosing a "hidden" star, and having to start again. The automatic slew to the (approximate) position of the second star, usually places that star, now easily visible, in the FOV of the finder or 32mm eyepiece.

[2STAR]

2 hours ago, Geoff Lister said:

I use the Stellarium planetarium program to select the bright stars. By advancing time, at dusk, Stellarium adds the names of the stars as they would become visible to the naked eye. By doing the same, for the middle of each month of the year, I have produced a table of 24 stars, and for each month, identified the best 3, 4, or 5, and their direction (N, NW, W etc.), giving good azimuth and altitude separation, and avoiding local trees, fences and buildings.

I use Synscan "Brightest Star" alignment, so I only need to see the first star to do a manual slew to its location. The handset suggests the second star, and this is where the list helps me from choosing a "hidden" star, and having to start again. The automatic slew to the (approximate) position of the second star, usually places that star, now easily visible, in the FOV of the finder or 32mm eyepiece.

I find Synscan far easier and more accurate than Nexstar.

Eric

[JOC]

My advice would be to download synscan init 2 to a mobile phone, turn on the GPS for a few minutes and use the given settings to set up the handheld goto unit remembering that it likes things like leading zeros, and American date formats.

Oh yes and not to commence the calibration until the scope is set in a horizontal position and facing astronomical North.