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Hi everyone,
I am in the process of purchasing a used G-11 with Losmandy digital setting
circles and polar alignment scope from a fellow club member. After years of
using fork mounts, I'm still getting used to using German mounts and I have
a few questions that don't seem to be really covered in the manuals, mostly
about the DSCs. Fortunately, the current owner is allowing me to borrow the
mount before actually purchasing it so I can "kick the tires" and get any
questions answered up front.

1) The manual states that the polar bore scope should rotate freely when
inserted in the RA housing. However, after tightening the retaining ring,
the finder won't budge. Is it normal to have to loosen the retaining ring
slightly to rotate the polar finder?

2) Will the DSCs in alt-az mode with the G-11?

3) Will the polar scope give me a sufficiently close alignment that the DSCs
will work with a 1-star alignment?

4) Appendix A in the DSC manual describes a process for determining the +90
degree position for the telescope/mount that is necessary for a 2-star
alignment with a GEM. Shimming the mount may be all fine and dandy if you
have a permanent installation, but it sounds impractical if you have to
setup and take down the scope and mount for every viewing session. How
accurate does this process have to be? Will centering Polaris and setting
the mechanical declination circle get me close enough?

5) The illuminator and battery pack for the polar bore scope seems a little
cumbersome. Is there an illuminator available with a self-contained
battery?

I'm sure I'll have other questions as I start using the mount.

Thanks,
================================================
Ray Porter
Applications Analyst Programmer
Administrative Information Services, UNC-CH
Phone: 966-5878
email: ray_porter@...
dragon@...
Home Page:

"Meddle not in the affairs of dragons,
for thou art crunchy and taste good with ketchup."

Ray,

You should be able to turn the polar finder without releasing the
locking ring. The polar finder may be stuck from old grease??

You can't use the DSC's in alt-az mode on a GEM. You CAN use them
without polar aligning.

You do need to do two star alignments initially. Generally the first
alignment may be off by quite a bit, but the second if done well with
bring everything into alignment. After two stars, I am still off a bit,
so I use "guide" to M13 which is easily picked up in my finderscope as a
third and final alignment target.
If you leave the DSC's powered up all of the time via AC then you
obviously would not need to worry about aligning. Just occasionally
update by aligning on any target.

The polar alignment scope will give you a very close polar alignment
though, enough to test CCD's for focus, study clusters or nebula, watch
for comet or neo movements, etc.. Take your time. Every effort here only
pays off in the long runs.

I am not sure of the +90 question. There is an initial balancing of the
GEM and initializing to 0 DEC (for my DSC's) which is a process I have
to do each time I set up. After a few times, it requires a little
effort. The LX200 series does make this process a lot easier, granted.

Your polar finder illuminator sounds like an older model, mine is from
JMI and has small actuator button with the built in battery compartment.
About an inch square for the whole thing. You may be able to change to
newer switch if they are sold independant of the polar finder. Give JMI
a call.

Hope this helps.

Take care,
Gregory david Stempel
FIREFRAME

Hi Gregory,
Thanks for replying. The previous owner of the mount is of the opinion that
the polar finder will get me close enough to use the DSCs with only a 1-star
alignment. Do you agree?

I'm almost certainly going to buy this mount. It is being offered to me at
about 1/2 the price for a new mount, DSCs and other accessories and as far
as I can determine, it is in pretty much new condition. Are there other
accessories I should consider getting? I'm certain I'm going to want the
side-by-side saddle plate. Are the RA/Dec replacement clutch knobs useful?
The replacement knobs for the screws that attach the mount to the tripod
look useful. Is a similar replacement knob available for the screw that
locks down the latitude adjustment? I hate fumbling with allen wrenches in
the dark.

There is no grease on the polar scope or where it mounts. I have the polar
scope, a small, white plastic washer that fits against a flange on the
widest part of the polar scope (not sure which side of the flange it goes
on, closest to the objective or the eyepiece?) and the retaining ring that
screws onto the RA housing to secure the polar scope. If I tighten the
retaining ring completely, the polar scope won't move (in fact, attempting
to move it only unscrews the retaining ring). Should there be a second
washer or something to allow the polar scope to float against the retaining
ring and the RA housing?

Is a dust cover of some kind available to protect the polar scope if it is
left in place all the time and to close the end of the RA housing when the
polar scope is not in place?

Here's what the manual says about setting the scope to +90 degrees when
doing a 2-star alignment with a GEM:

Losmandy DSC Manual, Section 5.3, Page 6
"When you are prompted for 1 or 2-star alignment, select 2-star. You will
be prompted to set the scope to +90 degrees. This means relative to the
scope, not the sky. For instance, if the scope is on a fork mount, it
should be positioned parallel to the form arms. For a German Eq, the scope
should be parallel the polar shaft.

For fork mounts, this positioning is not very critical (within a degree or
so is fine). If the mount is a German Eq, you must set this position with
some accuracy. See appendix (A) which describes a method for determining
the +90 degree position for German equatorial."

Appendix A describes a method for determining the +90 degree point by
sighting on Polaris and rotating the scope from one side of the mount to the
other -- centering Polaris using the alt-az controls on one side and shims
on the other (not something I particularly want to do every time I set the
scope up).

There is something else I noticed last night. The manual, in the section on
calibrating the mechanical declination setting circle, a set screw to lock
down the dec circle is mentioned. The manual also says the screw should be
between 0 and 10 degrees declination. I can't find that screw anywhere. Is
it so small that it is hard to see or is my mount an older model that is
missing something?

Thanks,
================================================
Ray Porter
Applications Analyst Programmer
Administrative Information Services, UNC-CH
Phone: 966-5878
email: ray_porter@...
dragon@...
Home Page:

"Meddle not in the affairs of dragons,
for thou art crunchy and taste good with ketchup."

Ray Porter wrote:

Hi Gregory,
Thanks for replying. The previous owner of the mount is of the opinion that
the polar finder will get me close enough to use the DSCs with only a 1-star
alignment. Do you agree?

Just want to mention that my G-11 polar scope gets me close enough to do
CCD imaging with no further refinement. I've tried to improve with drift alignment
(which I did for years with my previous mount) but found it wasn't necessary.

I've also found the 1 star alignment is fine for my DSCs. In order to place
a deepsky object on my CCD chip however (often a 12' x 8' piece of
sky), I usually find it necessary to realign on a nearby double star.

take care,
Rockett Crawford
----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)

How long are your exposures? The polar alignment scope on my older GM100
attaches to the side of the RA housing and is woefully inaccurate. I have
to drift for nearly an hour to get accurate alignment.

Paul

--- Rockett Crawford <Rockett@...> wrote:

Just want to mention that my G-11 polar scope gets me close enough to do
CCD imaging with no further refinement. I've tried to improve with drift
alignment (which I did for years with my previous mount) but found it
wasn't necessary.

__________________________________________________
Do You Yahoo!?
Yahoo! Mail - Free email you can access from anywhere!

Paul Sterngold wrote:

How long are your exposures? The polar alignment scope on my older GM100
attaches to the side of the RA housing and is woefully inaccurate. I have
to drift for nearly an hour to get accurate alignment.

I sum integrations, but as far as the polar alignment goes, it
is the same as a continuous exposure. I typically do 60 to
90 minute shots.

Here is a 90 minute shot at 1375mm focal length/9u pixels


Rockett Crawford

Paul

--- Rockett Crawford <Rockett@...> wrote:

Just want to mention that my G-11 polar scope gets me close enough to do
CCD imaging with no further refinement. I've tried to improve with drift
alignment (which I did for years with my previous mount) but found it
wasn't necessary.

----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)

Sorry to respond to my own post, but I wanted to add that the
G-11 polar alignment scope is mounted directly through the
polar axis of the mount.

Rockett Crawford wrote:

Paul Sterngold wrote:

How long are your exposures? The polar alignment scope on my older GM100
attaches to the side of the RA housing and is woefully inaccurate. I have
to drift for nearly an hour to get accurate alignment.

I sum integrations, but as far as the polar alignment goes, it
is the same as a continuous exposure. I typically do 60 to
90 minute shots.

Here is a 90 minute shot at 1375mm focal length/9u pixels


Rockett Crawford

----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)

This has been my experience with my one year old G11 too. I
have stopped drifting even for photography.

Pete

Just want to mention that my G-11 polar scope gets me close enough to do
CCD imaging with no further refinement. I've tried to improve with drift

alignment

(which I did for years with my previous mount) but found it wasn't

necessary.

I've also found the 1 star alignment is fine for my DSCs. In order to

place

a deepsky object on my CCD chip however (often a 12' x 8' piece of
sky), I usually find it necessary to realign on a nearby double star.

take care,
Rockett Crawford
--------------------------------------------------------------------------

--

Capella's Observatory (CCD Imaging)





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How long are you able to go in a single exposure without trailing?

Paul

--- Rockett Crawford <Rockett@...> wrote:

I sum integrations, but as far as the polar alignment goes, it
is the same as a continuous exposure. I typically do 60 to
90 minute shots.

__________________________________________________
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Yahoo! Mail - Free email you can access from anywhere!

My (actually, soon to be mine) polar scope also inserts through the polar
axis. There's no set screw that I've spotted yet. You just insert the
polar scope into the polar axis of the mount and screw down a retaining ring
to hold the finder in place. According to the manual the finder scope
should then rotate freely so you can align it with the position of the stars
in the sky (as seen with the naked eye). My problem is that once I tighten
down the retaining ring, the polar scope won't rotate.

As far as determining the correct +90 degree position, upon further
reflection I realized that the OTA could be shimmed within its rings. The
shims could then be left in place. I do think Gregory's suggestion about a
line level is probably a good one. All I need to do is make sure the OTA is
aligned with the polar axis of the mount, then lock down the mechanical
declination setting circle (assuming I can find the lock screw).

Thanks to everyone for their comments. This is a lot more mount than I've
ever used before and I'm still getting used to a German mount after years of
nothing but forks.

================================================
Ray Porter
Applications Analyst Programmer
Administrative Information Services, UNC-CH
Phone: 966-5878
email: ray_porter@...
dragon@...
Home Page:

"Meddle not in the affairs of dragons,
for thou art crunchy and taste good with ketchup."

Paul Sterngold wrote:

How long are you able to go in a single exposure without trailing?

Paul

--- Rockett Crawford <Rockett@...> wrote:

I sum integrations, but as far as the polar alignment goes, it
is the same as a continuous exposure. I typically do 60 to
90 minute shots.

It doesn't matter. Summed exposures are the same as a
continuous exposures as far as field rotation is concerned.

It doesn't matter if you sum 90 one minute shots or just take
one 90 minute shot. The same amount of field rotation will
show up in the shot either way.

(Actually there will be a little more field rotation in summed
shots because the field rotation keeps occurring in the
interval between integrations, during readout and the saving
of a file)

90 minutes is the longest I have shot so I can't say where
field rotation starts becoming apparent.


take care,
Rockett Crawford

----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)

Nice image of the Eagle Neb, Rockett. See my LRGB image of the same subject
at:



Taken with an SXP MX916 CCD camera through a 6" f/8 refractor on my GM100
mount. This is a sum of 3 x 5 mins luminance exposures, 1 x 5 mins each
RGB.

Paul Sterngold

--- Rockett Crawford <Rockett@...> wrote:

Here is a 90 minute shot at 1375mm focal length/9u pixels

__________________________________________________
Do You Yahoo!?
Yahoo! Mail - Free email you can access from anywhere!

Me too, but after I tweaked the polar alignment scope. A friend does one star
DSC alignments after using the polar scope.

Do a precise drift alignment and then check how far off your polar scope is,
adjust he polar scope reticle with the tiny screws, note that they all push on
the glass reticle, do not break the reticle. Good luck finding the allan wrench
for the scope, its smaller than 0.050"

Herm

"Peter Santangeli" <psantangeli@...> wrote:

This has been my experience with my one year old G11 too. I
have stopped drifting even for photography.

Pete

Just want to mention that my G-11 polar scope gets me close enough to do
CCD imaging with no further refinement. I've tried to improve with drift

alignment

Astropics

20 to 90 minutes..

Herm

Paul Sterngold <psterngold@...> wrote:

How long are your exposures? The polar alignment scope on my older GM100
attaches to the side of the RA housing and is woefully inaccurate. I have
to drift for nearly an hour to get accurate alignment.

Paul

Astropics

If you rotate the images prior to stacking, then you can cancel out field
rotation (obviously some of the rotation, not all)...in other words, you do x-y
adjustments on your images to stack, but if you also do a rotation of one of the
images then field rotation is canceled.

I can stack two 90 min exposures, there is noticeable rotation on one of the
images to make them align. Picture Window Pro will do this kind of alignment.

Herm

Rockett Crawford <Rockett@...> wrote:

It doesn't matter. Summed exposures are the same as a
continuous exposures as far as field rotation is concerned.

It doesn't matter if you sum 90 one minute shots or just take
one 90 minute shot. The same amount of field rotation will
show up in the shot either way.

Astropics

Very nice!, very high resolution, you can see an eagle within an eagle, both of
them diving to the 4:00 position. Take a look at mine:



Herm

Paul Sterngold <psterngold@...> wrote:

Nice image of the Eagle Neb, Rockett. See my LRGB image of the same subject
at:



Taken with an SXP MX916 CCD camera through a 6" f/8 refractor on my GM100
mount. This is a sum of 3 x 5 mins luminance exposures, 1 x 5 mins each
RGB.

Paul Sterngold

Astropics

Paul Sterngold wrote:

Nice image of the Eagle Neb, Rockett. See my LRGB image of the same subject
at:



Taken with an SXP MX916 CCD camera through a 6" f/8 refractor on my GM100
mount. This is a sum of 3 x 5 mins luminance exposures, 1 x 5 mins each
RGB.

That's really nice Paul. Looks good.

Rockett Crawford

----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)

hermperez@... wrote:

If you rotate the images prior to stacking, then you can cancel out field
rotation (obviously some of the rotation, not all)...in other words, you do x-y
adjustments on your images to stack, but if you also do a rotation of one of the
images then field rotation is canceled.

I can stack two 90 min exposures, there is noticeable rotation on one of the
images to make them align. Picture Window Pro will do this kind of alignment.

Herm

That's a good point Herm. Someone could take shorter exposures,
de-rotate, and register them if they needed to during image processing
as long as no one image smeared.

A friend of a friend of mine was supposed to have been experimenting
with shooting through an alt-az arrangment doing this with very short
integrations.


take care,
Rockett Crawford

----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)

hermperez@... wrote:

Very nice!, very high resolution, you can see an eagle within an eagle, both of
them diving to the 4:00 position. Take a look at mine:

Beautiful shot Herm.


Rockett Crawford

----------------------------------------------------------------------------

Capella's Observatory (CCD Imaging)