Re: GPS on a German Equatorial Mount


I don't understand either. What does an Alt/Az mount have to do with a
proper GE? The GE will only work if polar aligned and it could really
care less where it is on earth. For visual use, polar alignment by
pointing in the general direction by looking through the polar axis
hole and centering Polaris is plenty close enough. For Goto syncing I
just power up, GOTO a star east of the meridian, manually adjust the
scope to center that star, sync on it and carry on.

For astro-photography, the closer you want to shoot to the pole, the
better the polar alignment has to be to remove field rotation. I
regularly use just the PAS to align for astrophotography for object
further from the pole than 50 degrees or more. Syncing the scope is
identical to the above.

If you are doing astro-photography closer than about 50 degrees from
the pole with long deep shots or asteroid or supernova searches or
photometry with multiple targets through the night then excellent
polar alignment is required. If you are doing long exposure
astro-photography then flipping around the sky to multiple targets is
not an issue. Tricking GTO alignment can even come in handy. Say you
have an object you want to shoot but the database goto doesn't match
your selected positioning for field composition. You can "GOTO" your
selected object, move the scope with the direction buttons to select
your field framing, "RCAL" with the keypad, move the scope away using
the keypad direction buttons to focus on a nearby star or calibrate
the guider or whatever and when done, goto that object again to place
you right back where you wanted to be. Only in the case of multiple
target solutions over the course of a night would high accuracy goto
be required. In this case mount modeling would be nice but this is
normally the purvey of a fixed instrument. As well, target selection,
mount control, and data acquisition for multiple targets is really the
forte of computer software. If you have a computer then there is a lot
of modeling software available for less than the cost of putting it in
a keypad that will most likely go completely unused. Remember that the
keypad is just another planetarium program and has NO input on
pointing performed by any external coumputer controlled pointing!

In summary, in my opinion, GPS data is not required by the mount.

--- In ap-gto@..., "Joel" <jeguthals@...> wrote:


Yes, I understand that the Celestron Alt/Az mount needs the data
supplied by the GPS to work, but it is the same data that has to
supplied to the AP900GTO and the Losmandy/Gemini systems to make
their GOTO features work. What I do is take my Garmin GPS with me
when I go to a remote location, and use its longitude and latitude
data to enter into the AP computer, and I also use the GPS to check
the clock. It is very convenient to allow the GPS to download the
data automatically as the Nexstar GPS system allows rather than enter
the data manually. Thanks.


--- In ap-gto@..., chris1011@ wrote:

In a message dated 6/16/2007 5:09:10 PM Central Daylight Time,
jeguthals@ writes:

I have a NX11GPS that I use for star
parties and the GPS feature is great--accurate location and time
entered automatically at the beginning of every session. No

You have a GPS in the Celestron BECAUSE it is Alt-Azimuth and
requires it. The Celestron would NOT work without it, do you
understand this? You
cannot do without GPS in this scope, since tracking is absolutely
dependent on
your location. That does not mean that you need GPS to make your
work, or a German equatorial. GEMS have always worked just fine for
hundreds of
years before any satellites were put up there, but now that
satellites are up
there, computerized alt-az mounts are a possibility for the masses.


See what's free at

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