-----Original Message-----
From: Philippe BODART [mailto:phbodart@club-internet.fr]
Sent: Monday, April 17, 2000 10:15 AM
To: AP-GTO List;
Subject: [ap-gto] Safe zone of the 600E GTO mount.

Hi everybody

I am a newbie on this list.
I am retired and I live in Provence in the South of France.
I built an observatory above my garage in the garden.
I received my new telescope one month ago.
It is a 155 EDFS refractor with a 600E GTO mount.

For the moment I am fighting with the problem of the safe zone.
I understand it is the angle between the optical axis and the vertical
under which the OTA could hit the tripod (or the pier in my case).
In other respects the overturn zone is comprised between the hour angles
of 10:40 (OTA towards West) and 22:40 or - 1:20 (OTA towards East).
As a result there is a very large safe zone for the hour angles
close to -1:20.I give more details hereafter.
Did you make the same observations?
(I apologize if the subject has already been discussed in your list).
Is there anybody at ASTROPHYSICS I could write to?
Which e-mail?

Thank you for advising me.
Regards
Philippe Bodart.

1.Overturn zone.

The overturn zone is comprised between the hour angles of 10:40
(OTA towards West) and 22:40 or - 1:20 (OTA towards East).
This zone is independant of the set up of the safe zone (see further on).
It operates if you ask for a "go to".On the other hand with the keypad
buttons you can reach any point geometrically accessible.

It is tricky as it is possible to leave the hour movement working for a
while
without any trouble after having reached the aimed object.
Unfortunately it increases the size of the safe zone when the OTA
is close to the vertical towards East (see further on).
It is a pity that this zone cannot be set up.

2.Safe zone.

It is the angle between the optical axis and the vertical under
which the OTA could hit the tripod (or the pier in my case).
The most dangerous zone is obviously related to an hour angle of -1:20
(see above).I decided to recut the collar of my pier but you will see
that it remains relatively annoying with a camera.
With HA = -1:20 I rotated the OTA until it hit the pier and I noted
the related value of the declination.The safe angle is the complement
to 90 of the altitude (that can be calculated as a function of the hour
angle,
of the declination and of the latitude of the site with the ad'hoc trigo
formula).The safe angle is not the same according to the way you are
going towards the pier (N side or S side).
My results are the following:
-with an eyepiece 16(N side) and 18 (S side).
-with the camera "horizontal" 23(N side) and 16(S side).
-with the camera "vertical" 16 (N side) and 16 (S side).
You see that with the maximum allowed set up of 20 it remains
a risk with the camera "horizontal" (in fact parallel to the RA axis,
that allows you to have the N upside on the photos).
The set up of the safe zone prevents the OTA from tilting less than the
requested value to the vertical , even if it is not dangerous.
It is the case for hour angles bigger than 0:00 for example (the system
ignores the azimuth).
If you ask for a "go to" to a position comprised in the safe zone there
is no movement and the keyboard displays the following message:
"Outside safe zone.Slewing canceled".
On the other hand with the keypad buttons you can reach any point
geometrically accessible.

Once again it is a pity you cannot set up the overturn zone as the choice
made by the manufacturer spoils the safe zone.
On the other hand it is a pity that the system ignores the azimuth when
deciding if the movement is dangerous or not.
It took me a long time to realize all that and it is also a pity that
the handbook is not more explicit.