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Using OnStep


When OnStep is powered up it's default condition is to keep the stepper motors off (saves power,) so no commands that would result in stepper movement are carried out.  As explained below, starting the Align powers the stepper motors up and begins tracking.  Other commands do the same: Un-Park, Sync, and the Start Tracking command.  Some of these can be used to allow independent operation from "non OnStep aware" applications.

A few users just want tracking to start immediately when OnStep is powered up.  I don't recommend this but there is a Config.xxx.h option (#define AUTOSTART_TRACKING_ON) just be sure to use extra caution since limits of motion are ineffective/disabled in this case!  To switch to Goto operation with limits enabled let OnStep know you have manually moved back to the home position with the [Home(Reset)] button in the Android App, Sky Planetarium, etc.  You can then use OnStep as described below.


Mount Orientation

When starting OnStep (or after a reset) it always assumes the telescope is in the polar home position. That means the polar axis (RA axis) and telescope are pointing at the North Celestial Pole (NCP/roughly where Polaris is.) For southern hemisphere users it's the South Celestial Pole (SCP) that you want the polar axis and telescope pointing at.

For a German Equatorial Mount (GEM) the counterweight should be down (|HA|=6.)

For a Fork Mount (or similar) the forks should be left and right of the OTA (HA=0.) For a one-star align start with the finder-scope down, for two/three star align start with the finder-scope on top.

For Alt/Az telescopes, Dobsonains etc, you start in the polar home position - which just means the mount is carefully leveled and the telescope is roughly pointing at the NCP (or SCP.)

  • Tip: Your mount might have a manual that describes the polar alignment procedure (specific to its polar finder perhaps) and if not you can find much helpful advice on the internet.  The Starizona site, for example, has a nice tutorial on polar alignment.
  • Tip: If your mount doesn't have clutches and you need to use OnStep to move to the polar home position you can do so by enabling tracking or starting an Align (see below.)  Then use a guide control (N/S/E/W pad,) and a fast guide rate setting, to move the 'scope.  Finally use a Reset (At Home) command to tell OnStep this is the polar home position and that you are "starting over."

Site

The site information specifies the Latitude, Longitude, and UTC Offset (opposite of a Time Zone value.)  The Android App (Menu->Site Selection,) website, and ASCOM driver all have facilities to upload site information.  Sky Planetarium can be configured to send the site information when connecting.  Many 3rd party planetarium programs (etc.) can do the same.

  • Tip: Since OnStep remembers these settings site info. usually only needs to be updated if your observing location has changed since the last use.  When the observing location (site) does change the Android App can use GPS (if available) to automatically fill the site information for quick upload.

Date/time

OnStep needs the current date and time to locate celestial coordinates and know where the limits of motion are.  The date/time can be sent up by commands or automatically retrieved from an RTC (a real time clock, like the DS3234) at startup.  The Android App has a button to set the date/time.  The website has a clock button that does the same.  My Sky Planetarium can be configured to automatically send up the date/time whenever you connect.  Many 3rd party planetarium programs (etc.) can do the same.

Alignment

Now that OnStep has the correct site information and date/time you can start an Align, depending on your configuration, up to 9 stars may be used.  Generally its best pick stars that are a bit away from the NCP or SCP and spread out across the sky.  For a GEM type mount its a good idea to have stars on both sides of the Meridian.

Android App/Smart Hand Controller:

In the Android App and SHC start an align then a list of suitable stars will be displayed to choose from. Pick a bright easily identified star and do a goto. If the mount is well constructed and polar aligned and OnStep was setup correctly the star should be in a wide field eyepiece of a small telescope or in your finder 'scope. Use the guide controls to center the star in the eyepiece. Then accept the alignment point.  For the Android App you need to then press and hold the "Align" button on the direction pad.  For the SHC simply press the center button.  If more alignment stars are required the list of stars will reappear and this sequence will repeat until done.

Sky Planetarium:

In Sky Planetarium the "ASCOM Telescope Control" dialog has has controls to initiate the alignment.  Again, pick bright easily identified star(s).  Do a goto (right-click map and select goto) to the first star.  Center the star then in the "Control" dialog then right-click on the map and select "Telescope accept align".  Repeat this process for each align star until done.

In addition to this functionality there is "Goto Assist" in Sky Planetarium which works with OnStep to do high precision n-star alignment.  Documentation for using this (and other alignment methods) is in Sky Planetarium's built-in help.

The OnStep Website:

If you have the WiFi or Ethernet add-on the website also provides the ability to set the date/time/location and perform a multi-star alignment working side-by-side with 3rd party applications.  The process is similar to that described above.

Other Planetarium Programs:

In lieu of using the above Sky Safari, CdC, etc. can perform a Sync (similar to a 1-Star Align) or simply enable Tracking to get going.

Use

You're now ready to find objects. Since this example is for a 1-star align the accuracy will be somewhat less than what a 3-star align can do (for example) and you might want to do a goto and sync on a nearby bright star every now and then to help with pointing accuracy depending on how far you travel from location to location in the sky.

If using an Android tablet this is where I usually exit my App and start Sky Safari and connect for control from there.