New GPS Hand Control
4 June 2002
During late May 2002, Celestron started shipping a new version of hand control with
their NexStar 8 GPS and 11 GPS telescopes. This new version is 1.6 while the
original version was 1.2 - see the Odds & Ends section for determining the version
number of your scope. Additionally, it should be noted that most of the items in this review also apply to
the iComp hand control for the new N5i and N8i; it has virtually all the same features as
the N8/11 GPS hand control.
As I have stated in my other reviews of NexStar telescopes, it has
always been my opinion that the NexStar telescopes (all models) have been a clear step
above any other computerized telescope (or self-contained computer add-on) for ease of
use. The direct access to common catalogs, such as Messier and NGC, is far superior
to anything else I've seen. This should not to be considered too lightly since ease of use
directly affects how much time you spend punching keys on the hand control compared to how
much time you spend looking through the eyepiece.
The N8/11 GPS line has been remarkably trouble-free since it's introduction, but there
were some flaws. The most serious was the source of vibration that was remedied by a
motor control (MC) board replacement to upgrade the MC firmware to version 3.0 or
higher. There is more info about the upgraded MC at the Odds & Ends link above
and it should be noted that some of the new features I will discuss below require
MC version 3.0 or higher. Some of the features will actually require the MC to be
upgraded to version 4.0; Celestron will release details for this procedure soon. See
the Odds & Ends section for instructions to determine the version on your scope.
First, here is the list of well-known flaws in the original GPS hand control (HC) and
the status in this new version:
- No cordwrap prevention feature - added in this HC.
- Error in the coordinates of M2, M10 and M110 - fixed.
- No compensation for the difference in magnetic and true North - added in this HC.
I will discuss this more below.
- Filter limits reference the base of the scope, rather than the local horizon (only an
issue when the scope is mounted on a wedge) - in the new HC, filter limits now reference
local horizon, while slew limits still reference the base of the scope in order to protect
larger accessories (cameras, etc.) during 'goto' slews.
Many other changes are included as well:
- You can now check the version of the HC and MC firmware via the Menu - no more
"press 6, then 7, be careful not to hit the wrong buttons or you might ruin your
- Calibrate Compass - after performing a successful alignment in Alt-Az mode the Calibrate
Compass function allows your scope to calculate and store the difference between true and
magnetic North at your location. Future GPS alignments will then know the correct
offset and act accordingly. On my scope, it is common for the two alignment stars to
be very near the center of the finder scope during the alignment routine. This
method is more accurate than static magnetic declination tables, but if you travel far
with your scope you may need to recalibrate - a wise solution in my opinion.
- Hibernate mode - after your scope is properly aligned (GPS, two-star, polar, etc.) you
can set it to 'Hibernate' and then turn the power off. The next time you power on
the scope, the alignment will still be accurate. This is useful if your scope is
mounted in an observatory, when leaving your scope setup at a weekend star party, or when
you desire to observe the Sun or planets during the day. In the last case, you would
align the night before, hibernate the scope and the next day 'goto' will place the Sun or
planets in the field of view.
- To protect equipment attached to the scope, during GPS alignment the scope now dips
about 10 degrees before seeking level. This prevents the original alarming behavior
of looping over 180 degrees at the beginning of GPS alignment. Previously we
prevented this by insuring the optical tube assembly (OTA) was pointed below level prior
to starting an alignment, now it is sufficient to start with the OTA pointed roughly
- Polar alignment routine - unfortunately I am mostly a visual astronomer and do not own a
wedge, so I cannot fully comment on this feature. Basically, this new routine
simplifies the alignment process by providing GPS Alignment on a wedge. If an imager
would like to comment on this new feature, I would be glad to post it here.
- The HC provides new RS-232 commands for setting tracking rate. This allows a
PC/Mac program to directly move the scope in the same fashion as the arrow buttons on the
- There are now 32-bit RS-232 'goto' and 'get' commands. This provides a software
resolution of 0.083 and will allow software such as PinPoint and TPoint to provide
the type of extremely accurate goto performance required for the most demanding
- The final direction on a 'goto' slew has been changed to right and down (direction of
the front of the scope when viewed from behind the scope) - this is the correct motion to
minimize backlash in the gears due to the back-heavy nature of the N8/11 GPS scopes.
- Final direction on 'goto' slews can be user selected. This can be useful when the
scope is balanced differently, particularly with a Fastar camera which will likely make
the scope front-heavy rather than the usual back-heavy.
- For visual use, tracking in Alt-Az mode is now virtually perfect. Objects stay in
the field of view for hours.
- User objects have been increased to 200 sky and 200 land objects, an increase from 25 of
each in the original HC.
- View Time-Site now displays Time-Zone and Daylight Savings settings to eliminate
confusion as to the current state of these parameters.
- Improved ephemeris calculations now put the Moon right in the field of view every time.
- The time zones in the HC now match international conventions and for areas outside of
the United States they are simply your offset from UTC.
- There are menu functions to move the scope to level and move the scope to North.
- Coupled with MC version 4, the 'goto' slew now gets to its new coordinates a bit faster.
This is most noticeable when you perform a second 'goto' to the same object. The
familiar left-and-dip (actually hop now) movement does not move as far from the object
before returning and the final slow-rate movements are shorter.
- And while talking about MC version 4, it provides silent tracking.
After a slew, you will hear nothing when the scope is tracking ... owners of
coffee-grinder scopes will be green (or is it blue :-) with envy.
Celestron has made substantial improvements in their flagship product. While the
original GPS was a fine product, the further refinement of the NexStar line is testament
to Celestron's commitment to their customers. The upgrade was well worth the wait!