Mounts - two quick questions

What's the difference between a German EQ mount and a 'normal' one?

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?

"Alan" wrote in message
...
What's the difference between a German EQ mount and a 'normal' one?

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?




What do think 'normal' is? I always thought german EQ was a normal mount for
an astronomical telescope.


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Alan wrote:
What's the difference between a German EQ mount and a 'normal' one?

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?

The German EQ mounts comes with built-in brass music 8-)

No, seriously, a german equatorial *is* a 'normal' equatorial. Of course, a
fork mount on a wedge is also equatorial, so a german equatorial identifies
the design used by e.g. Vixen GP-DX and similar mounts. Btw., here is a
picture of a German EQ (a Vixen GP-DX)
http://home.online.no/~arnholm/astro..._east_gpdx.jpg

A DEC motor is not a *must* in all cases, but it is very handy for some
uses:

* Manual slewing in 2 directions (using a dual axis controller). Much easier
than manual handling for one axis and motor for the other.

* If you are using autoguiding with imaging, you may want to autoguide also
in DEC, and then a DEC motor is needed.

Clear skies
Carsten A. Arnholm
http://home.online.no/~arnholm/astro/astro.htm
N59.776 E10.457

On Tue, 18 Nov 2003 21:45:28 +0000 (UTC), "Yunus"
wrote:


"Alan" wrote in message
...
What's the difference between a German EQ mount and a 'normal' one?

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?

I think the German mount is the "normal" one with two axes and
corresponding counterweight. There are other EQ mounts like the fork
mount and also EQ platforms for altazimuth mounted scopes to sit on.

I wish I had the dec axis motor for my mount as it could be used for
aligning the scope "remotely" - I can't reach my knob when looking
through the EP (though this has nothing to do with astronomy!). It
would also help with fine movements with less wobble/vibration when
working at high magnification.

Mark

Alan wrote:
What's the difference between a German EQ mount and a 'normal' one?

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?

The German eq mount is usually the crap one. Unless the manufacturer is
either outstandingly creative or stupifyingly inept, any other eq design is
demonstrably more stable. The reason the German design is so pervasive is
that it is by far the easiest precision mount to mass produce - hence it's
cheap. However designing one that actually works kinematically is absolutely
non-trivial and the renders the product extremely expensive, (see
http://www.scsastro.co.uk/it250009.htm). Just about any other design of
mounting you care to consider is better than a German one. .

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?

Although not stated in the manuals, usually it's to allow some means of
countering minor inaccuracies in the polar alignment of the mounting. On
permanently mounted scopes, it allows corrections to be applied for
differential refraction of the atmosphere and to allow guiding on moving
objects such as comets or asteroids.

Regards
Chef!

In message , Chef!
writes
Alan wrote:

Why would you ever want to motorise the dec axis (assuming you are not
GOTO-ing) ? I.e. why are there dual-axis motors?

Although not stated in the manuals, usually it's to allow some means of
countering minor inaccuracies in the polar alignment of the mounting. On
permanently mounted scopes, it allows corrections to be applied for
differential refraction of the atmosphere and to allow guiding on moving
objects such as comets or asteroids.

I would say the ability to have a GO-TO facility has been the bigger
reason for most of the last fifteen years.
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" The German eq mount is usually the crap one. Unless the manufacturer is
either outstandingly creative or stupifyingly inept, any other eq design
is
demonstrably more stable. The reason the German design is so pervasive is
that it is by far the easiest precision mount to mass produce - hence it's
cheap. However designing one that actually works kinematically is
absolutely
non-trivial and the renders the product extremely expensive, (see
http://www.scsastro.co.uk/it250009.htm). Just about any other design of
mounting you care to consider is better than a German one. .
Regards
Chef!


I would respectfully disagree with this statement as it is misleading as the
original post was probably referring to the options for a beginner. You
could be comparing the German Eq with some thing like an English cradle
mount which indeed is an extremely stable design, but hardly an off the
shelf item for a first time buyer! But for the 'normal equipment' you will
see in a shop, I consider the German Eq to be one of the most stable designs
that are commercially available and by your own quote is cheap for the
precision. I would be interested in what the other 'demonstrably more
stable' designs are and how the costs compare to the 'good ol GEM'.

Regards
Dave Rose