Scope Setup

Scope Setup configures MaxPoint for your telescope. All settings in this dialog box are extremely important for accurate telescope modelling. Be sure to set them accurately.

Note: MaxPoint gets the current Universal Time from Windows directly. You must make sure that your computer clock is set accurately, including the time zone and daylight savings time settings.

Important: if you set your computer clock to GMT, use (GMT) Casablanca, Monrovia not (GMT) Greenwich Mean Time : Dublin, Edinburgh, Lisbon, London, because the latter locations use daylight savings time. If you use the latter setting, Windows will calculate Universal Time incorrectly during the summer months.

Click Select Telescope to choose the ASCOM telescope driver for your instrument. The ASCOM Chooser will display a list of telescope drivers. Note that you must set the telescope Properties before the chooser will allow you to click OK. (Tip: if you want to experiment with MaxPoint before using it on a telescope, pick the Telescope Simulator.)

You can set up a custom local Horizon for your location. The horizon limit will restrict the list of alignment stars, and limit the positions used for auto-calibration, but it does not restrict telescope pointing. You can point beyond these limits from your telescope control application.

The Latitude and Longitude are essential for determining the correct telescope mount model. Enter the Lat (deg N+) and Long (deg E+) in DD MM SS.S format; for example, if you are at 45 degrees, 30 minutes north, then enter 45 30. An ultra-precise position is not required, but it should be accurate to better than a degree.

Two numbers are necessary for calculating atmospheric refraction. Atm (kPa) is the atmospheric pressure in kilopascals. Standard pressure at sea level is 101.3 kPa (equivalent to 1013 millibars). If your scope has built-in atmospheric correction set this value to zero. The ambient air temperature T (C) must also be entered in degrees Celsius. Using these two values, MaxPoint will calculate and correct for atmospheric refraction at low altitudes.

If you have a German Equatorial mount, turn on German. In this mode, MaxPoint will perform slightly different modelling when the telescope is on the west and east sides of the pier. MaxPoint also tries to guess when the telescope flips over the pier.

The Flip limit E (deg) and Flip Limit W (deg) settings tell MaxPoint when to assume the telescope has flipped. Typically the GOTO controllers allow the telescope to go past the meridian a certain distance before forcing a flip. If this is set to 5 degrees, MaxPoint will assume the telescope has not flipped until it moves more than 5 degrees past the meridian. Some mounts flip at different points when moving East to West and West to East; see below for an explanation of the two controls. Note that if MaxPoint guesses incorrectly, you can correct the setting by changing the West of pier setting in the Control Panel.

Flip Limit E (east) applies when the telescope is on the East side of the mount, and attempts to cross the meridian. The telescope is allowed to go past the meridian (i.e. to the west) by this amount before the telescope's GOTO controller flips it over.

Flip Limit W (west) applies when the telescope is on the West side of the mount, and attempts to cross the meridian. The telescope is allowed to go past the meridian (i.e. to the east) by this amount before the telescope's GOTO controller flips it over.

To determine the correct values, try adjusting the telescope mount in small steps, and observe when it actually flips. (Note that since RA is measured in hours, not degrees, one minute of RA is actually 15 arc-minutes.)

For some telescopes, especially fork mounts, there may be a maximum declination; going above this limit may cause a collision between your camera equipment and the mount. You can enter the maximum declination in Dec Limit; this will prevent MaxPoint from trying to use calibration fields in this area.  

Alt Limit provides a similar limit for altitude. Note that this only prevents MaxPoint from issuing a command to slew to a position inside the limit; it is possible for the telescope to slew through the region on a long slew. If you do not wish to limit the altitude, set this to 90 degree.

Enforce Slew Limits will cause MaxPoint to refuse a request from a controlling program to slew to coordinates within the Alt Limit and Dec Limit zones. MaxPoint will throw an exception, which should be reported to the user by the controlling software. Note that a slew through the altitude cannot be prevented by MaxPoint since it is up to the telescope's built-in computer to determine the slew trajectory.

Anti-Backlash can be turned on to reduce inaccuracies caused by backlash in the mount. When this is on, the telescope will always make two moves instead of one.  The first move will offset the telescope in both RA and Declination by twice the amount specified in Backlash (Arc Sec). The second move will position the telescope on-target. The initial offset is always in the same direction, so the telescope will always approach the final destination from the exact same direction. The offset of the first slew is double the amount of backlash specified, to make absolutely sure that the backlash is completely removed. This safety factor is used because backlash often varies somewhat from position to position. Note that some popular mounts have 120 arc-seconds of backlash or more.

During automatic calibration, the Slew Pause (sec) setting allows time for the mount to settle down after a slew operation, before an exposure is taken. This may help prevent streaked exposures, because some mounts take a second or two to resume normal sidereal tracking, especially if Anti-Backlash is not enabled. For most telescopes, this can be set to zero if Anti-Backlash is in use. This has no effect when using the nudge or manual slew controls.

When Anti-Backlash is on, the option 1st AB Slew Pause is enabled. When this option is off, the Slew Pause is applied only to the second part of the two-stage anti-backlash slew operation. Turn this on if your telescope requires a pause after each and every slew, including the initial slew of the two-stage anti-backlash operation.

For most telescopes, the epoch used for positions is the "epoch of date". This means that precession and nutation are taken into account when sending positions to the telescope. A few telescopes do the conversion from J2000 automatically within their electronics; in that case only, you should turn on the J2000 check box.

The Poll Interval determines how often MaxPoint asks the telescope for its current position. Setting a shorter time updates the scope position display more often; however, some telescopes respond extremely slowly, and this can in turn slow down operation of the software. You can slow down the rate by increasing the number above 1 second. In general it is not necessary to reduce this number below 1 second.

Once all the settings are made, click OK to save them, or Cancel to throw out the changes.