Date   

Some pictures updated

marcolorenzi70
 

Dear all, I eventually found little time to update my home page with 8 new shots. They all were taken with my worthy 900GTO

The direct links to the images and the preview is accessible here
http://astrosurf.com/lorenzi/lastupdate.htm

All shots were made using my STL11K (now sold) and relative to the following objects:

M 51 the Whirlpool Galaxy, one of my preferred objects (Vixen Visac 20cm f/9)

M106 Another nice galaxy, quite extended (Vixen Visac 20cm f/9)

M65/66/NGC3628 The popular Leo Triplet (Vixen Visac 20cm f/9)

M97/M108 The intriguing Owl Nebula and its neighbour galaxy (Vixen Visac 20cm f/9)

M1 The Crab Nebula (Vixen Visac 20cm f/9)

M78 A charming reflecting nebula in Orion (Vixen Visac 20cm f/9)

NGC2264 The Christmas three and its jewels (Tec140)

M42 The Great Orion Nebula, this picture made with data from both the TEC140 and the Visac to increase core details

Comments and critics are welcome
Can't wait to have a chance to test my just arrived Mach1, perhaps under a thruly dark sky ^_^

Clear Skies
Marco Lorenzi
http://astrosurf.com/lorenzi/


Tante idee per la salvaguardia del nostro Pianeta su Yahoo! For Good
http://it.promotions.yahoo.com/forgood/environment.html


Re: PASILL4 on Mach1, update

Muhammed Samir Kharusi
 

At least from what you have drawn, the indication is that the
magnification is correct. It is thus fairly simple to verify that the
reticle is correctly engraved or not. Take a photograph, daytime
against a clear sky or a white sheet of paper, through the polar
scope. Just try various lenses on a digicam or dslr holding the lens
against the eyepiece. Something always works well enough. Match up
your photo, ie using Image Link, with The Sky. My old version of The
Sky did not show the location of the North Celestial Pole, but I
added it in as a user point. Be careful that you put it in for 2008!
The error in the sketch does seem to be too large to be blamable on
atmospheric refraction, IMHO, and if it is indeed in error, Losmandy
should be able to produce corrected reticles fairly quickly.

--- In ap-gto@yahoogroups.com, "phenrotay" <Pierre.Henrotay@...>
wrote:

Larry,

yes, I did.
PEMPro is giving slightly different results compared to PAM but of
the
same order of magnitude.
I used PAM because I am used to it (and it is fastest).
Images taken after polar alignment using PAM show no significant
drift
on 4 minutes exposures, at 2 arcsec/pixel. When the alignment is
done
using the PASILL4 only, the images for the same object and duration
show an evident drift - as expected from a 10 arcminutes
misalignment.

Pierre

--- In ap-gto@yahoogroups.com, "Larry Phillips" <llp41astro@> wrote:

Have you tried precise polar aligning using other methods besides
PAM? I have had mixed results using PAM, especially if you use
the
entire process. I have better success if I only reiterate the
initial 3 exposure step. Try drift align or one of AP's
alignment
methods to be sure it is the alignment scope and not the
alignment
procedure. Just a thought. I am usually very close after a
polar
scope alignment and need to make only small adjustments with a
precision alignment technique. I have a PASILL4 which I received
in
March.

Larry


Re: Focuser Backlash

Larry Phillips
 

Joe,
I have the same focuser motor that you have and it is on the 4"
FeatherTouch focuser on my new AP140 scope. I just assumed I had
back lash because the numbers I was getting from FocusMax were not
perfect. There was a 3.0 PI number and the bottom of the V was not
very pointed. This is only the second time I have used FocusMax so I
am still learning. But I just read that the offset PI number from
being in the center is due to the initial and final focus positions
that I use. Anyway, I thought maybe there might be some backlash I
could reduce out of the focuser.

Larry

--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@...> wrote:

Sorry, I must have misunderstood your post. Could you be more
explicit,
what focuser do you have and how did you determine you have
backlash in it?
Thkx...joe :)


"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Larry Phillips" <llp41astro@...>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 5:42 PM
Subject: [ap-gto] Re: Focuser Backlash


Everything is working fine. After getting a series of profiles I
thought maybe I could improve things. I did not know you could
correct backlash with the software. My original question was
making
a correction mechanically to the focuser. I will give your
suggestions a try.

Larry

--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@> wrote:

Larry, you can adjust your Backlash in either FMx itself or in
FT's
Driver
ASCOM window. L.Webber says not to use both. Go into FMx's
System
tab,
there you'll see FMx's Backlash settings. Click on Settings to
have the
ASCOM window displayed. On my AP155 using the FTF-3545 w/FT's
Digital
MicroFocuser motor I have 'both' set to Zero. Great combination.
BTW,
there's a FMx Yahoo group,
http://tech.groups.yahoo.com/group/FMaxUG/ ...joe
:)

PS: You didn't mention if you're experiencing any other problems.
Just in
case, be sure your focuser Locking knob is completely loose. The
FT Motor
holds my STL11K, A-P Field Flattener and adapters without
trouble.

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Larry Phillips" <llp41astro@>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 11:40 AM
Subject: [ap-gto] Focuser Backlash


After using FocusMax with my new AP 140 4" focuser using a
FeatherTouch
motor, I am wondering if there is anyway to adjuct the focuser
backlash.

Larry


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Re: Focuser Backlash

Joe Mize
 

Sorry, I must have misunderstood your post. Could you be more explicit, what focuser do you have and how did you determine you have backlash in it? Thkx...joe :)


"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Larry Phillips" <llp41astro@cox.net>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 5:42 PM
Subject: [ap-gto] Re: Focuser Backlash


Everything is working fine. After getting a series of profiles I
thought maybe I could improve things. I did not know you could
correct backlash with the software. My original question was making
a correction mechanically to the focuser. I will give your
suggestions a try.

Larry

--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@...> wrote:

Larry, you can adjust your Backlash in either FMx itself or in FT's
Driver
ASCOM window. L.Webber says not to use both. Go into FMx's System
tab,
there you'll see FMx's Backlash settings. Click on Settings to
have the
ASCOM window displayed. On my AP155 using the FTF-3545 w/FT's
Digital
MicroFocuser motor I have 'both' set to Zero. Great combination.
BTW,
there's a FMx Yahoo group,
http://tech.groups.yahoo.com/group/FMaxUG/ ...joe
:)

PS: You didn't mention if you're experiencing any other problems.
Just in
case, be sure your focuser Locking knob is completely loose. The
FT Motor
holds my STL11K, A-P Field Flattener and adapters without trouble.

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Larry Phillips" <llp41astro@...>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 11:40 AM
Subject: [ap-gto] Focuser Backlash


After using FocusMax with my new AP 140 4" focuser using a
FeatherTouch
motor, I am wondering if there is anyway to adjuct the focuser
backlash.

Larry


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

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see http://groups.yahoo.com/group/ap-gtoYahoo! Groups Links





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

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Re: DEC Backlash and RA "Drift" on AP1200GTO

Joe Mize
 

Richard not to get into a long discussion, I was just providing something Roland posted in a similar thread to yours earlier this year. His advice in both cases matches what I've been doing for quite some time now with great success...joe :)

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Richard Seavey" <reseavey@verizon.net>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 4:03 PM
Subject: Re: [ap-gto] Re: DEC Backlash and RA "Drift" on AP1200GTO


Joe
In paragraph 1), Roland is saying that he does a calibration at the
equator, and uses it for all other declinations. That might work OK
depending on what is causing the errors in RA to occur, but if the errors
are from something like a gust of wind, then it could take a lot of guide
cycles to correct that error. I think that correcting the RA guide speed
for declination is a better approach and is what I do. I'm sure that
Roland's technique works well if used for correcting such things as worm
periodic error.

In paragraph 2), it seems to say that one has to calibrate the guider with
the binning set to 1x1. I don't believe that is true. Maxim adjusts the
guide speed depending on how the guide chip binning is set. The confusion
might be that in the "tutorial" section of the MaxIm manual, it says to set
the binning to 1x1. I think that was just for the tutorial and not a
general statement. The detailed information in chapter 6 of the manual says
nothing about using 1x1 for calibration. Just my 2 cents.

Richard



At 02:14 AM 4/27/2008 -0400, you wrote:

Jim & Richard, I saved a post from Roland back on 02-19 in "Re: [ap-gto]
Guide star drifting in RA" thread.

At the time it made since but reading it now it's a little convoluted
without knowing went on beforehand. The important two things I saved it for
was what Roland said,

1) In his first paragraph he said don't use the Guider Tab's DEC Co-ordinate
box. I do this myself. If you're unfamiliar with this technique I'll 'try'
to explain. Set the DEC box to '0' and Uncheck the "Use Scope DEC" in the
Guider dropdown list. Then calibrate my Guider on the Equator near the
Meridian where the sky moves its fastest. The further away form the Equator
you are guiding the slower the sky moves and the smaller the deviations.
With the Calibration on the Equator the numbers generated are sufficient to
correct those larger deviations yet when deviations occur further away from
the Equator the same numbers are used to make smaller corrections. (hope
you get jist of what I'm trying to say) My Calibration lasts as long as I
don't make changes to my imaging train. The last time I Calibrated my
Guider was months ago. This method works even if you're not permanently
mounted, works great. My RMS' are usually in the lower 0.0xx's. You should
be able to do so too.

2) I believe what Roland says in his second paragraph: "...(p.s. you didn't
bin the guider by any chance?)." means when you Calibrate your Guider you
need to do so in Bin-1 scale. MaximDL says the same thing and goes further
by saying to turn off Backlash in the Guider settings while Calibrating.

The following is Roland's response. I hope I interpreted correctly.
HTH...joe :)

===
I looked at Maxim and do not see what you are talking about on the uncheck
"use Scope Dec" Is this by chance the make simultaneous corrections?
No, It's under Options. If you have an older version of the software, there
is a place for you to enter the Dec co-ordinate. Always use zero here,
otherwise the software will reduce the correction level by the cosine of the
angle
that you enter, and this is not good.

If you look in your parameters, it should tell you what te pixel scale is,
and that should be somewhere close to what you calculate for your focal
length
and pixel size (p.s. you didn't bin the guider by any chance?). If it isn't,
then indeed the software will make smaller corrections than is needed to
bring
the star back to zero.

In order for you to guide successfully, you need to know what every number
means. If you do not, you will never be able to troubleshoot the guide loop,
and
certainly I cannot do it very well for you because I have no idea what is in
your various parameter windows.

Roland Christen
===

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Richard Seavey" <<mailto:reseavey%40verizon.net>reseavey@verizon.net>
To: <<mailto:ap-gto%40yahoogroups.com>ap-gto@yahoogroups.com>
Sent: Saturday, April 26, 2008 11:03 PM
Subject: Re: [ap-gto] Re: DEC Backlash and RA "Drift" on AP1200GTO

Hi Jim
Your rms guiding errors are quite similar to what I get. I image at 0.72
arc-sec per pixel, so on nights when the seeing is 2.5 arc-sec or better,
I
need to keep the errors below about 0.3 arc-sec rms. Even more important
is
to get the same error in both axis so that the stars aren't elongated. For
me, oval stars are a lot more annoying than slightly bigger stars. I am
using MaxIm to control the guiding and usually turn on the feature that
plots the guiding errors in real time. I know I have backlash in the DEC
axis, but need to measure it again so I can compare it to what you are
getting. My sub exposures are 10 minutes and guide exposures are usually
between 2 and 6 seconds. I have been using 3 pixels of dither and my max
move is 0.13 sec. It would be very interesting to see what others are
getting for guiding errors.

Richard


At 03:06 AM 4/26/2008 +0000, you wrote:

Hi Richard,

It varies. And CCDSoft doesn't provide those numbers in a convenient
fashion, so I have to go through each 8min exposure to mine them.

Here are a couple of samples from last night. All are 8min imaging
exposures, with 4sec guide exposures. The numbers are in arc-seconds:

1. RAmax = 0.824, RArms = 0.252, DECmax = 0.705, DECrms = 0.303
2. RAmax = 1.337, RArms = 0.323, DECmax = 1.054, DECrms = 0.329
3. RAmax = 1.970, RArms = 0.666, DECmax = 1.967, DECrms = 0.524

These were: (1) the best image of the night (perhaps the best result
I've EVER seen at my site with my gear), (2) a more typical image of
the night, and (3) the worst image of the night, respectively. CCDI
says the FWHMs were 1.94", 3.07", and 4.25", for the actual images,
respectively.

To be fair, the seeing did seem to change over the course of the
night, starting and ending reasonably well but deteriorating for 45min
or so in the middle.

I'm not sure how representative the above numbers truly are. Most
times I bother to calculate out this stuff the DEC rms errors are
actually larger than the RA rms errors (and both are generally larger
than the numbers shown above) which suggests to me that DEC errors are
going uncorrected for one reason or another, and I personally believe
that reason to be DEC backlash.

This was also shooting M81, which is pretty far north, and so the
periodic error is only 1/3 what it would be at the equator, in terms
of "true sky angle".

Cheers,
JS

--- In
<mailto:ap-gto%40yahoogroups.com><mailto:ap-gto%40yahoogroups.com>ap-gto@yahoogroups.com,
Richard
Seavey <reseavey@...> wrote:

Jim
What are your typical peak and rms guide errors in DEC and RA when your
seeing is in the 2-3 arc-sec range?

Richard



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Re: PASILL4 on Mach1, update

Pierre Henrotay
 

Larry,

yes, I did.
PEMPro is giving slightly different results compared to PAM but of the
same order of magnitude.
I used PAM because I am used to it (and it is fastest).
Images taken after polar alignment using PAM show no significant drift
on 4 minutes exposures, at 2 arcsec/pixel. When the alignment is done
using the PASILL4 only, the images for the same object and duration
show an evident drift - as expected from a 10 arcminutes misalignment.

Pierre

--- In ap-gto@yahoogroups.com, "Larry Phillips" <llp41astro@...> wrote:

Have you tried precise polar aligning using other methods besides
PAM? I have had mixed results using PAM, especially if you use the
entire process. I have better success if I only reiterate the
initial 3 exposure step. Try drift align or one of AP's alignment
methods to be sure it is the alignment scope and not the alignment
procedure. Just a thought. I am usually very close after a polar
scope alignment and need to make only small adjustments with a
precision alignment technique. I have a PASILL4 which I received in
March.

Larry


Re: PASILL4 on Mach1, update

Larry Phillips
 

Have you tried precise polar aligning using other methods besides
PAM? I have had mixed results using PAM, especially if you use the
entire process. I have better success if I only reiterate the
initial 3 exposure step. Try drift align or one of AP's alignment
methods to be sure it is the alignment scope and not the alignment
procedure. Just a thought. I am usually very close after a polar
scope alignment and need to make only small adjustments with a
precision alignment technique. I have a PASILL4 which I received in
March.

Larry

--- In ap-gto@yahoogroups.com, "phenrotay" <Pierre.Henrotay@...>
wrote:

Dear,

I started a few weeks ago a long thread concerning the usage of the
PASILL4 polar scope on my Mach1 (starting with post #21642).

Hereby the updated status.

I got the chance yesterday night to test my PASILL4 on a friend's
900GTO.
We rechecked that the reticle was aligned with the optical axis of
the polar scope (by rotating the reticle housing) and was aligned
with the RA axis of the 900GTO (by rotating the RA axis).
All was fine, no need for any change.

We reproduced equivalent results as the ones that I previously
obtained on my Mach 1, that is:
- using the PASILL4 - 3 stars visible -, we end up about 10
arcminutes from the pole
- after a computer assisted polar alignment (bringing us about 1
arcminute from pole), the position of the 3 stars do not match the
one expected from the engravings:
when Polaris is brought within its gap by rotating the reticle
housing, the 2 other stars are at about 20 degrees hour angle from
their expected position
I think we can exclude operator error - we double checked what we
were doing.

So it seems that the problem lies in my PASILL4 itself. Unless
anyone
has a better idea.

I hesitate in asking my dealer for a replacement, as I do not know
if
10 arcminutes misalignment is out of specs. Maybe I am expecting
too
much accuracy from it - I am used to the Vixen Atlux polar scope,
which allowed me to be routinely under 5 arcminutes
and under 2 arcminutes when used carefully, in a matter of seconds
of
time.

Also, Roland mentioned that if one reticle was defective, all would
be. So, if out of specs, it might be worth to have a global check
anyway from AP about this issue (potentially, it could be a general
error in the engravings ? such thing can happen, someone mentioned
a
problem in the past with scope magnification).

Unfortunately I have no way to access a "good working" PASILL4, as
someone suggested.
There is none close to where I live, only non-rotating (pre-
PASILL3)
models - these are difficult to use on the Mach1 and a test would
not
be representative.

For the moment, I will thus concentrate on using other techniques
(the quick drift, as explained in the manual, which now has
additional drawings and detailed lists of candidate stars, thank
for
this) and use the PASILL4 only for a coarse start.

Again, not a major issue but a bit frustrating.
I think AP mounts deserve a first-class polar scope (as Takahashi
and
Vixen do have), and - unless mine is specifically a lemon - this
one
does not match up.


Pierre

PS:
Some info to avoid repostings:
- the model is the newest one (with engravings till 2030)
- PoleAlignMax was used for achieving precise alignment and
measuring
misalignment


Re: Focuser Backlash

Larry Phillips
 

Everything is working fine. After getting a series of profiles I
thought maybe I could improve things. I did not know you could
correct backlash with the software. My original question was making
a correction mechanically to the focuser. I will give your
suggestions a try.

Larry

--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@...> wrote:

Larry, you can adjust your Backlash in either FMx itself or in FT's
Driver
ASCOM window. L.Webber says not to use both. Go into FMx's System
tab,
there you'll see FMx's Backlash settings. Click on Settings to
have the
ASCOM window displayed. On my AP155 using the FTF-3545 w/FT's
Digital
MicroFocuser motor I have 'both' set to Zero. Great combination.
BTW,
there's a FMx Yahoo group,
http://tech.groups.yahoo.com/group/FMaxUG/ ...joe
:)

PS: You didn't mention if you're experiencing any other problems.
Just in
case, be sure your focuser Locking knob is completely loose. The
FT Motor
holds my STL11K, A-P Field Flattener and adapters without trouble.

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Larry Phillips" <llp41astro@...>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 11:40 AM
Subject: [ap-gto] Focuser Backlash


After using FocusMax with my new AP 140 4" focuser using a
FeatherTouch
motor, I am wondering if there is anyway to adjuct the focuser
backlash.

Larry


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

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gtoYahoo! Groups Links




Re: DEC Backlash and RA "Drift" on AP1200GTO

Richard Seavey
 

Joe
In paragraph 1), Roland is saying that he does a calibration at the
equator, and uses it for all other declinations. That might work OK
depending on what is causing the errors in RA to occur, but if the errors
are from something like a gust of wind, then it could take a lot of guide
cycles to correct that error. I think that correcting the RA guide speed
for declination is a better approach and is what I do. I'm sure that
Roland's technique works well if used for correcting such things as worm
periodic error.

In paragraph 2), it seems to say that one has to calibrate the guider with
the binning set to 1x1. I don't believe that is true. Maxim adjusts the
guide speed depending on how the guide chip binning is set. The confusion
might be that in the "tutorial" section of the MaxIm manual, it says to set
the binning to 1x1. I think that was just for the tutorial and not a
general statement. The detailed information in chapter 6 of the manual says
nothing about using 1x1 for calibration. Just my 2 cents.

Richard

At 02:14 AM 4/27/2008 -0400, you wrote:

Jim & Richard, I saved a post from Roland back on 02-19 in "Re: [ap-gto]
Guide star drifting in RA" thread.

At the time it made since but reading it now it's a little convoluted
without knowing went on beforehand. The important two things I saved it for
was what Roland said,

1) In his first paragraph he said don't use the Guider Tab's DEC Co-ordinate
box. I do this myself. If you're unfamiliar with this technique I'll 'try'
to explain. Set the DEC box to '0' and Uncheck the "Use Scope DEC" in the
Guider dropdown list. Then calibrate my Guider on the Equator near the
Meridian where the sky moves its fastest. The further away form the Equator
you are guiding the slower the sky moves and the smaller the deviations.
With the Calibration on the Equator the numbers generated are sufficient to
correct those larger deviations yet when deviations occur further away from
the Equator the same numbers are used to make smaller corrections. (hope
you get jist of what I'm trying to say) My Calibration lasts as long as I
don't make changes to my imaging train. The last time I Calibrated my
Guider was months ago. This method works even if you're not permanently
mounted, works great. My RMS' are usually in the lower 0.0xx's. You should
be able to do so too.

2) I believe what Roland says in his second paragraph: "...(p.s. you didn't
bin the guider by any chance?)." means when you Calibrate your Guider you
need to do so in Bin-1 scale. MaximDL says the same thing and goes further
by saying to turn off Backlash in the Guider settings while Calibrating.

The following is Roland's response. I hope I interpreted correctly.
HTH...joe :)

===
I looked at Maxim and do not see what you are talking about on the uncheck
"use Scope Dec" Is this by chance the make simultaneous corrections?
No, It's under Options. If you have an older version of the software, there
is a place for you to enter the Dec co-ordinate. Always use zero here,
otherwise the software will reduce the correction level by the cosine of the
angle
that you enter, and this is not good.

If you look in your parameters, it should tell you what te pixel scale is,
and that should be somewhere close to what you calculate for your focal
length
and pixel size (p.s. you didn't bin the guider by any chance?). If it isn't,
then indeed the software will make smaller corrections than is needed to
bring
the star back to zero.

In order for you to guide successfully, you need to know what every number
means. If you do not, you will never be able to troubleshoot the guide loop,
and
certainly I cannot do it very well for you because I have no idea what is in
your various parameter windows.

Roland Christen
===

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Richard Seavey" <<mailto:reseavey%40verizon.net>reseavey@verizon.net>
To: <<mailto:ap-gto%40yahoogroups.com>ap-gto@yahoogroups.com>
Sent: Saturday, April 26, 2008 11:03 PM
Subject: Re: [ap-gto] Re: DEC Backlash and RA "Drift" on AP1200GTO

Hi Jim
Your rms guiding errors are quite similar to what I get. I image at 0.72
arc-sec per pixel, so on nights when the seeing is 2.5 arc-sec or better,
I
need to keep the errors below about 0.3 arc-sec rms. Even more important
is
to get the same error in both axis so that the stars aren't elongated. For
me, oval stars are a lot more annoying than slightly bigger stars. I am
using MaxIm to control the guiding and usually turn on the feature that
plots the guiding errors in real time. I know I have backlash in the DEC
axis, but need to measure it again so I can compare it to what you are
getting. My sub exposures are 10 minutes and guide exposures are usually
between 2 and 6 seconds. I have been using 3 pixels of dither and my max
move is 0.13 sec. It would be very interesting to see what others are
getting for guiding errors.

Richard


At 03:06 AM 4/26/2008 +0000, you wrote:

Hi Richard,

It varies. And CCDSoft doesn't provide those numbers in a convenient
fashion, so I have to go through each 8min exposure to mine them.

Here are a couple of samples from last night. All are 8min imaging
exposures, with 4sec guide exposures. The numbers are in arc-seconds:

1. RAmax = 0.824, RArms = 0.252, DECmax = 0.705, DECrms = 0.303
2. RAmax = 1.337, RArms = 0.323, DECmax = 1.054, DECrms = 0.329
3. RAmax = 1.970, RArms = 0.666, DECmax = 1.967, DECrms = 0.524

These were: (1) the best image of the night (perhaps the best result
I've EVER seen at my site with my gear), (2) a more typical image of
the night, and (3) the worst image of the night, respectively. CCDI
says the FWHMs were 1.94", 3.07", and 4.25", for the actual images,
respectively.

To be fair, the seeing did seem to change over the course of the
night, starting and ending reasonably well but deteriorating for 45min
or so in the middle.

I'm not sure how representative the above numbers truly are. Most
times I bother to calculate out this stuff the DEC rms errors are
actually larger than the RA rms errors (and both are generally larger
than the numbers shown above) which suggests to me that DEC errors are
going uncorrected for one reason or another, and I personally believe
that reason to be DEC backlash.

This was also shooting M81, which is pretty far north, and so the
periodic error is only 1/3 what it would be at the equator, in terms
of "true sky angle".

Cheers,
JS

--- In
<mailto:ap-gto%40yahoogroups.com><mailto:ap-gto%40yahoogroups.com>ap-gto@yahoogroups.com,
Richard
Seavey <reseavey@...> wrote:

Jim
What are your typical peak and rms guide errors in DEC and RA when your
seeing is in the 2-3 arc-sec range?

Richard




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Groups Links




Re: Focuser Backlash

Joe Mize
 

Larry, you can adjust your Backlash in either FMx itself or in FT's Driver ASCOM window. L.Webber says not to use both. Go into FMx's System tab, there you'll see FMx's Backlash settings. Click on Settings to have the ASCOM window displayed. On my AP155 using the FTF-3545 w/FT's Digital MicroFocuser motor I have 'both' set to Zero. Great combination. BTW, there's a FMx Yahoo group, http://tech.groups.yahoo.com/group/FMaxUG/ ...joe :)

PS: You didn't mention if you're experiencing any other problems. Just in case, be sure your focuser Locking knob is completely loose. The FT Motor holds my STL11K, A-P Field Flattener and adapters without trouble.

"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Larry Phillips" <llp41astro@cox.net>
To: <ap-gto@yahoogroups.com>
Sent: Sunday, April 27, 2008 11:40 AM
Subject: [ap-gto] Focuser Backlash


After using FocusMax with my new AP 140 4" focuser using a FeatherTouch
motor, I am wondering if there is anyway to adjuct the focuser backlash.

Larry


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Re: PASILL4 on Mach1, update

Pierre Henrotay
 

I placed a drawing, not meant to be 100% accurate but it gives a fair
idea of the respective positions: look in the files section:
http://tech.groups.yahoo.com/group/ap-gto/files/phenrotay/
with name
PASILL4-2.jpg

This is +- what it looks like when the alignment is accurate (< 1
arcmin) and when Polaris brought in its gap after rotating the
reticle housing.

Pierre

--- In ap-gto@yahoogroups.com, "Jeff" <jlc@...> wrote:

The stars are off in the same direction, correct?

Is the star even within the marks for precession?

I have a pasill4 on a 1200 but usually just always do drift
alignment when
imaging. For visual it doesnt have to be very accurate.

Right now, the mount is stowed, but if I get out soon I'll check it.
(Planning on it, but work is distracting me.)

jeff


Re: PASILL4 on Mach1, update

Jeff <jlc@...>
 

The stars are off in the same direction, correct?

Is the star even within the marks for precession?

I have a pasill4 on a 1200 but usually just always do drift alignment when
imaging. For visual it doesnt have to be very accurate.

Right now, the mount is stowed, but if I get out soon I'll check it.
(Planning on it, but work is distracting me.)

jeff



_____

From: ap-gto@yahoogroups.com [mailto:ap-gto@yahoogroups.com] On Behalf Of
phenrotay
Sent: Sunday, April 27, 2008 8:58 AM
To: ap-gto@yahoogroups.com
Subject: [ap-gto] PASILL4 on Mach1, update



Dear,

I started a few weeks ago a long thread concerning the usage of the
PASILL4 polar scope on my Mach1 (starting with post #21642).

Hereby the updated status.

I got the chance yesterday night to test my PASILL4 on a friend's
900GTO.
We rechecked that the reticle was aligned with the optical axis of
the polar scope (by rotating the reticle housing) and was aligned
with the RA axis of the 900GTO (by rotating the RA axis).
All was fine, no need for any change.

We reproduced equivalent results as the ones that I previously
obtained on my Mach 1, that is:
- using the PASILL4 - 3 stars visible -, we end up about 10
arcminutes from the pole
- after a computer assisted polar alignment (bringing us about 1
arcminute from pole), the position of the 3 stars do not match the
one expected from the engravings:
when Polaris is brought within its gap by rotating the reticle
housing, the 2 other stars are at about 20 degrees hour angle from
their expected position
I think we can exclude operator error - we double checked what we
were doing.

So it seems that the problem lies in my PASILL4 itself. Unless anyone
has a better idea.

I hesitate in asking my dealer for a replacement, as I do not know if
10 arcminutes misalignment is out of specs. Maybe I am expecting too
much accuracy from it - I am used to the Vixen Atlux polar scope,
which allowed me to be routinely under 5 arcminutes
and under 2 arcminutes when used carefully, in a matter of seconds of
time.

Also, Roland mentioned that if one reticle was defective, all would
be. So, if out of specs, it might be worth to have a global check
anyway from AP about this issue (potentially, it could be a general
error in the engravings ? such thing can happen, someone mentioned a
problem in the past with scope magnification).

Unfortunately I have no way to access a "good working" PASILL4, as
someone suggested.
There is none close to where I live, only non-rotating (pre-PASILL3)
models - these are difficult to use on the Mach1 and a test would not
be representative.

For the moment, I will thus concentrate on using other techniques
(the quick drift, as explained in the manual, which now has
additional drawings and detailed lists of candidate stars, thank for
this) and use the PASILL4 only for a coarse start.

Again, not a major issue but a bit frustrating.
I think AP mounts deserve a first-class polar scope (as Takahashi and
Vixen do have), and - unless mine is specifically a lemon - this one
does not match up.

Pierre

PS:
Some info to avoid repostings:
- the model is the newest one (with engravings till 2030)
- PoleAlignMax was used for achieving precise alignment and measuring
misalignment


PASILL4 on Mach1, update

Pierre Henrotay
 

Dear,

I started a few weeks ago a long thread concerning the usage of the
PASILL4 polar scope on my Mach1 (starting with post #21642).

Hereby the updated status.

I got the chance yesterday night to test my PASILL4 on a friend's
900GTO.
We rechecked that the reticle was aligned with the optical axis of
the polar scope (by rotating the reticle housing) and was aligned
with the RA axis of the 900GTO (by rotating the RA axis).
All was fine, no need for any change.

We reproduced equivalent results as the ones that I previously
obtained on my Mach 1, that is:
- using the PASILL4 - 3 stars visible -, we end up about 10
arcminutes from the pole
- after a computer assisted polar alignment (bringing us about 1
arcminute from pole), the position of the 3 stars do not match the
one expected from the engravings:
when Polaris is brought within its gap by rotating the reticle
housing, the 2 other stars are at about 20 degrees hour angle from
their expected position
I think we can exclude operator error - we double checked what we
were doing.

So it seems that the problem lies in my PASILL4 itself. Unless anyone
has a better idea.

I hesitate in asking my dealer for a replacement, as I do not know if
10 arcminutes misalignment is out of specs. Maybe I am expecting too
much accuracy from it - I am used to the Vixen Atlux polar scope,
which allowed me to be routinely under 5 arcminutes
and under 2 arcminutes when used carefully, in a matter of seconds of
time.

Also, Roland mentioned that if one reticle was defective, all would
be. So, if out of specs, it might be worth to have a global check
anyway from AP about this issue (potentially, it could be a general
error in the engravings ? such thing can happen, someone mentioned a
problem in the past with scope magnification).

Unfortunately I have no way to access a "good working" PASILL4, as
someone suggested.
There is none close to where I live, only non-rotating (pre-PASILL3)
models - these are difficult to use on the Mach1 and a test would not
be representative.

For the moment, I will thus concentrate on using other techniques
(the quick drift, as explained in the manual, which now has
additional drawings and detailed lists of candidate stars, thank for
this) and use the PASILL4 only for a coarse start.

Again, not a major issue but a bit frustrating.
I think AP mounts deserve a first-class polar scope (as Takahashi and
Vixen do have), and - unless mine is specifically a lemon - this one
does not match up.


Pierre

PS:
Some info to avoid repostings:
- the model is the newest one (with engravings till 2030)
- PoleAlignMax was used for achieving precise alignment and measuring
misalignment


Focuser Backlash

Larry Phillips
 

After using FocusMax with my new AP 140 4" focuser using a FeatherTouch
motor, I am wondering if there is anyway to adjuct the focuser backlash.

Larry


Re: DEC Backlash and RA "Drift" on AP1200GTO

Joe Mize
 

Jim & Richard, I saved a post from Roland back on 02-19 in "Re: [ap-gto] Guide star drifting in RA" thread.

At the time it made since but reading it now it's a little convoluted without knowing went on beforehand. The important two things I saved it for was what Roland said,

1) In his first paragraph he said don't use the Guider Tab's DEC Co-ordinate box. I do this myself. If you're unfamiliar with this technique I'll 'try' to explain. Set the DEC box to '0' and Uncheck the "Use Scope DEC" in the Guider dropdown list. Then calibrate my Guider on the Equator near the Meridian where the sky moves its fastest. The further away form the Equator you are guiding the slower the sky moves and the smaller the deviations. With the Calibration on the Equator the numbers generated are sufficient to correct those larger deviations yet when deviations occur further away from the Equator the same numbers are used to make smaller corrections. (hope you get jist of what I'm trying to say) My Calibration lasts as long as I don't make changes to my imaging train. The last time I Calibrated my Guider was months ago. This method works even if you're not permanently mounted, works great. My RMS' are usually in the lower 0.0xx's. You should be able to do so too.

2) I believe what Roland says in his second paragraph: "...(p.s. you didn't bin the guider by any chance?)." means when you Calibrate your Guider you need to do so in Bin-1 scale. MaximDL says the same thing and goes further by saying to turn off Backlash in the Guider settings while Calibrating.

The following is Roland's response. I hope I interpreted correctly. HTH...joe :)

===
I looked at Maxim and do not see what you are talking about on the uncheck
"use Scope Dec" Is this by chance the make simultaneous corrections?
No, It's under Options. If you have an older version of the software, there
is a place for you to enter the Dec co-ordinate. Always use zero here,
otherwise the software will reduce the correction level by the cosine of the angle
that you enter, and this is not good.

If you look in your parameters, it should tell you what te pixel scale is,
and that should be somewhere close to what you calculate for your focal length
and pixel size (p.s. you didn't bin the guider by any chance?). If it isn't,
then indeed the software will make smaller corrections than is needed to bring
the star back to zero.

In order for you to guide successfully, you need to know what every number
means. If you do not, you will never be able to troubleshoot the guide loop, and
certainly I cannot do it very well for you because I have no idea what is in
your various parameter windows.

Roland Christen
===


"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Richard Seavey" <reseavey@verizon.net>
To: <ap-gto@yahoogroups.com>
Sent: Saturday, April 26, 2008 11:03 PM
Subject: Re: [ap-gto] Re: DEC Backlash and RA "Drift" on AP1200GTO


Hi Jim
Your rms guiding errors are quite similar to what I get. I image at 0.72
arc-sec per pixel, so on nights when the seeing is 2.5 arc-sec or better, I
need to keep the errors below about 0.3 arc-sec rms. Even more important is
to get the same error in both axis so that the stars aren't elongated. For
me, oval stars are a lot more annoying than slightly bigger stars. I am
using MaxIm to control the guiding and usually turn on the feature that
plots the guiding errors in real time. I know I have backlash in the DEC
axis, but need to measure it again so I can compare it to what you are
getting. My sub exposures are 10 minutes and guide exposures are usually
between 2 and 6 seconds. I have been using 3 pixels of dither and my max
move is 0.13 sec. It would be very interesting to see what others are
getting for guiding errors.

Richard


At 03:06 AM 4/26/2008 +0000, you wrote:

Hi Richard,

It varies. And CCDSoft doesn't provide those numbers in a convenient
fashion, so I have to go through each 8min exposure to mine them.

Here are a couple of samples from last night. All are 8min imaging
exposures, with 4sec guide exposures. The numbers are in arc-seconds:

1. RAmax = 0.824, RArms = 0.252, DECmax = 0.705, DECrms = 0.303
2. RAmax = 1.337, RArms = 0.323, DECmax = 1.054, DECrms = 0.329
3. RAmax = 1.970, RArms = 0.666, DECmax = 1.967, DECrms = 0.524

These were: (1) the best image of the night (perhaps the best result
I've EVER seen at my site with my gear), (2) a more typical image of
the night, and (3) the worst image of the night, respectively. CCDI
says the FWHMs were 1.94", 3.07", and 4.25", for the actual images,
respectively.

To be fair, the seeing did seem to change over the course of the
night, starting and ending reasonably well but deteriorating for 45min
or so in the middle.

I'm not sure how representative the above numbers truly are. Most
times I bother to calculate out this stuff the DEC rms errors are
actually larger than the RA rms errors (and both are generally larger
than the numbers shown above) which suggests to me that DEC errors are
going uncorrected for one reason or another, and I personally believe
that reason to be DEC backlash.

This was also shooting M81, which is pretty far north, and so the
periodic error is only 1/3 what it would be at the equator, in terms
of "true sky angle".

Cheers,
JS

--- In <mailto:ap-gto%40yahoogroups.com>ap-gto@yahoogroups.com, Richard
Seavey <reseavey@...> wrote:

Jim
What are your typical peak and rms guide errors in DEC and RA when your
seeing is in the 2-3 arc-sec range?

Richard



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

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Re: DEC Backlash and RA "Drift" on AP1200GTO

Richard Seavey
 

Hi Jim
Your rms guiding errors are quite similar to what I get. I image at 0.72
arc-sec per pixel, so on nights when the seeing is 2.5 arc-sec or better, I
need to keep the errors below about 0.3 arc-sec rms. Even more important is
to get the same error in both axis so that the stars aren't elongated. For
me, oval stars are a lot more annoying than slightly bigger stars. I am
using MaxIm to control the guiding and usually turn on the feature that
plots the guiding errors in real time. I know I have backlash in the DEC
axis, but need to measure it again so I can compare it to what you are
getting. My sub exposures are 10 minutes and guide exposures are usually
between 2 and 6 seconds. I have been using 3 pixels of dither and my max
move is 0.13 sec. It would be very interesting to see what others are
getting for guiding errors.

Richard

At 03:06 AM 4/26/2008 +0000, you wrote:

Hi Richard,

It varies. And CCDSoft doesn't provide those numbers in a convenient
fashion, so I have to go through each 8min exposure to mine them.

Here are a couple of samples from last night. All are 8min imaging
exposures, with 4sec guide exposures. The numbers are in arc-seconds:

1. RAmax = 0.824, RArms = 0.252, DECmax = 0.705, DECrms = 0.303
2. RAmax = 1.337, RArms = 0.323, DECmax = 1.054, DECrms = 0.329
3. RAmax = 1.970, RArms = 0.666, DECmax = 1.967, DECrms = 0.524

These were: (1) the best image of the night (perhaps the best result
I've EVER seen at my site with my gear), (2) a more typical image of
the night, and (3) the worst image of the night, respectively. CCDI
says the FWHMs were 1.94", 3.07", and 4.25", for the actual images,
respectively.

To be fair, the seeing did seem to change over the course of the
night, starting and ending reasonably well but deteriorating for 45min
or so in the middle.

I'm not sure how representative the above numbers truly are. Most
times I bother to calculate out this stuff the DEC rms errors are
actually larger than the RA rms errors (and both are generally larger
than the numbers shown above) which suggests to me that DEC errors are
going uncorrected for one reason or another, and I personally believe
that reason to be DEC backlash.

This was also shooting M81, which is pretty far north, and so the
periodic error is only 1/3 what it would be at the equator, in terms
of "true sky angle".

Cheers,
JS

--- In <mailto:ap-gto%40yahoogroups.com>ap-gto@yahoogroups.com, Richard
Seavey <reseavey@...> wrote:

Jim
What are your typical peak and rms guide errors in DEC and RA when your
seeing is in the 2-3 arc-sec range?

Richard


Re: DEC Backlash and RA "Drift" on AP1200GTO

Bill Bradford
 

Glad you posted this, Anthony. I was going to ask you in your previous post if you were dithering.

Joe's post was of great benefit to me since (now that I have a Mach1, my tracking and guiding will be good enough to NEED dithering, unlike with my previous mount :>), and I would have gone crazy trying to dither with so short a max move.

I have always used about .3 secs as max move on my old mount and would have used that with the Mach1 while trying to dither.

Bill

----- Original Message -----
From: ayiomamitis
To: ap-gto@yahoogroups.com
Sent: Saturday, April 26, 2008 2:47 AM
Subject: [ap-gto] Re: DEC Backlash and RA "Drift" on AP1200GTO


--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@...> wrote:
>
> Jim, change you Max Move from 0.2sec to 2.0sec. 0.2sec limits the
> correction to a Maximum drive time of 0.2sec. Changing to 2.0sec will allow
> you to correct longer excursions and Dither moves. I actually have mine set
> to 3.0sec because of the size of my Dither moves...joe :)

Aha! Now perhaps I see why the Dither plugin for CCDSoft was hanging on my machine. I
will go back and check but this time using a purposely much higher setting for MAX.

Thanks Joe!

Anthony.

>
>
> "May You Go Among The Imperishable Stars"
> Joe Mize www.cav-sfo.com
> Chiefland Astronomy Village, Fla.
>
> ----- Original Message -----
> From: "Jim S." <blues_rule_solomon_1999@...>
> To: <ap-gto@yahoogroups.com>
> Sent: Friday, April 25, 2008 3:53 PM
> Subject: [ap-gto] DEC Backlash and RA "Drift" on AP1200GTO
>
>
> > Hi,
> >
> > I've got some questions about getting the best possible guiding
> > results out of my AP1200. It's performing better than any mount I've
> > ever owned, by a mile, but there might be some room for me to improve
> > my results, which is the topic of this post.
> >
> > Dec Backlash:
> >
> > First, I've measured my DEC backlash at mean = 12.55", sigma = 3.59".
> > (See below for the method I'm using.) A friend and I removed the DEC
> > cover and one of the reduction gears, and could not "feel" any
> > backlash in the worm gear to worm wheel mesh. Rather, it looked to us
> > as if all or most of that backlash was in the mesh among the reduction
> > gears, in which we could indeed feel some slop.
> >
> > DEC Backlash is causing me some grief in guiding, as I can see the
> > tell-tale signs of the DEC axis "wandering between the rails" when
> > looking at the Autoguider.log file in CCDSoft, with the result that
> > DEC errors take many guide-exposure periods to correct. Sometimes it
> > takes CCD Commander a long time to "dither" because it has to unwind
> > the backlash, and sometimes it gives up because it takes too long to
> > reach my minimum-error threshold before kicking off an exposures. And
> > in so dithering in the DEC direction, it almost always overshoots.
> >
> > I'm using the "Roland-approved" guiding parameters: guide rate = 1x
> > Sidereal, min = 0.02s, max = 0.2s, backlash compensation = OFF, and
> > calibration time = 30s, guide exposures = 4s (sometimes longer), PEC =
> > ON, Aggressiveness = 8; and my polar alignment error is VERY small,
> > well less than an arc-minute according to PAM and verified with a
> > drift. The measured calibration speeds agree with the analytical
> > computed values to within tenths of a percent, so indeed the
> > calibration results are "correct".
> >
> > My question is thus: Is it possible on the AP1200 to adjust the
> > reduction-gear mesh to trim some of this backlash? If indeed the
> > "slop" is in the reduction gears, then I don't believe "intentional
> > DEC misbalance" will help as a "solution" to this problem, though
> > perhaps intentional polar misalignment -- to induce some drift in a
> > constant direction -- might help. I think this latter case, however,
> > is inevitable when atmospheric refraction and ANY polar alignment
> > error is taken into account. And there will be an inevitable
> > "reversal" when dithering.
> >
> > RA "Drift":
> >
> > My long-term RA "drift" has an odd shape that I can't quite explain,
> > and fitting a curve to that "drift" is imperative when using PEMPro to
> > dial in an optimal PE curve. I've uploaded a chart to my web site for
> > inspection:
> >
> > http://www.SaratogaSkies.com/tmp/ra-drift.gif
> >
> > The spot data is the instantaneous RA error (with PEC off) measured by
> > PEMPro. The solid line is a "curve fit" I've done which is simply a
> > moving average of the instantaneous errors, wherein the "window" of
> > that moving average is equal to the worm period (382.95 seconds).
> >
> > Can someone explain why the "RA drift" curve has the odd shape it
> > does? I would expect it to be roughly monotonically increasing or
> > decreasing, as polar misalignment and/or atmospheric refraction affect
> > the apparent RA of the star.
> >
> > Could this be the reduction gears at work? Or perhaps flexure/sagging
> > of the camera/focuser? I'm using a 6" refractor with the FT3545
> > focuser, and an all-threaded coupling between a ST-2000XM camera and
> > the focuser, and the data was collected at DEC=0 beginning JUST west
> > of the Meridian and running for roughly 8 worm periods.
> >
> > More importantly, is this indicative of any issue with the mount? Or
> > is it just a long-term, slowly varying "drift", that I shouldn't sweat
> > because it can be easily guided out?
> >
> > Backlash Measurement Method:
> >
> > For those interested, here's how I'm measuring DEC Backlash:
> >
> > 1. Preload the DEC gear by moving (at 1x Sidereal) in the Y+ direction
> > (I use the "move" buttons in PulseGuide for this).
> > 2. Do a calibration in CCDSoft of a specified calibration time.
> > 3. Derive DEC backlash from the measured Y+ and Y- speeds.
> >
> > Note: Y+ is the first direction that CCDSoft moves in DEC, and then it
> > moves the same amount in Y-.
> >
> > I then compute the DEC Backlash as follows:
> >
> > DEC backlash = (Y+ - Y-) * Tc * Res
> >
> > where:
> >
> > o Y+ and Y- are the speeds in pixels/second measured by CCDsoft (px/s)
> > o Tc is the calibration time in seconds (s)
> > o Res is the imaging scale produced by my scope/camera combination in
> > arc-seconds/pixel ("/s)
> >
> > Is this method valid? If not, why not?
> >
> > Thanks for any help/advice you folks might be able to offer.
> >
> > Cheers,
> > Jim S.
> >
> >
> > ------------------------------------
> >
> > To UNSUBSCRIBE, or for general information on the ap-gto list
> > see http://groups.yahoo.com/group/ap-gtoYahoo! Groups Links
> >
> >
> >
> >
>


Re: DEC Backlash and RA "Drift" on AP1200GTO

ayiomamitis
 

--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@...> wrote:

Jim, change you Max Move from 0.2sec to 2.0sec. 0.2sec limits the
correction to a Maximum drive time of 0.2sec. Changing to 2.0sec will allow
you to correct longer excursions and Dither moves. I actually have mine set
to 3.0sec because of the size of my Dither moves...joe :)
Aha! Now perhaps I see why the Dither plugin for CCDSoft was hanging on my machine. I
will go back and check but this time using a purposely much higher setting for MAX.

Thanks Joe!

Anthony.



"May You Go Among The Imperishable Stars"
Joe Mize www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Jim S." <blues_rule_solomon_1999@...>
To: <ap-gto@yahoogroups.com>
Sent: Friday, April 25, 2008 3:53 PM
Subject: [ap-gto] DEC Backlash and RA "Drift" on AP1200GTO


Hi,

I've got some questions about getting the best possible guiding
results out of my AP1200. It's performing better than any mount I've
ever owned, by a mile, but there might be some room for me to improve
my results, which is the topic of this post.

Dec Backlash:

First, I've measured my DEC backlash at mean = 12.55", sigma = 3.59".
(See below for the method I'm using.) A friend and I removed the DEC
cover and one of the reduction gears, and could not "feel" any
backlash in the worm gear to worm wheel mesh. Rather, it looked to us
as if all or most of that backlash was in the mesh among the reduction
gears, in which we could indeed feel some slop.

DEC Backlash is causing me some grief in guiding, as I can see the
tell-tale signs of the DEC axis "wandering between the rails" when
looking at the Autoguider.log file in CCDSoft, with the result that
DEC errors take many guide-exposure periods to correct. Sometimes it
takes CCD Commander a long time to "dither" because it has to unwind
the backlash, and sometimes it gives up because it takes too long to
reach my minimum-error threshold before kicking off an exposures. And
in so dithering in the DEC direction, it almost always overshoots.

I'm using the "Roland-approved" guiding parameters: guide rate = 1x
Sidereal, min = 0.02s, max = 0.2s, backlash compensation = OFF, and
calibration time = 30s, guide exposures = 4s (sometimes longer), PEC =
ON, Aggressiveness = 8; and my polar alignment error is VERY small,
well less than an arc-minute according to PAM and verified with a
drift. The measured calibration speeds agree with the analytical
computed values to within tenths of a percent, so indeed the
calibration results are "correct".

My question is thus: Is it possible on the AP1200 to adjust the
reduction-gear mesh to trim some of this backlash? If indeed the
"slop" is in the reduction gears, then I don't believe "intentional
DEC misbalance" will help as a "solution" to this problem, though
perhaps intentional polar misalignment -- to induce some drift in a
constant direction -- might help. I think this latter case, however,
is inevitable when atmospheric refraction and ANY polar alignment
error is taken into account. And there will be an inevitable
"reversal" when dithering.

RA "Drift":

My long-term RA "drift" has an odd shape that I can't quite explain,
and fitting a curve to that "drift" is imperative when using PEMPro to
dial in an optimal PE curve. I've uploaded a chart to my web site for
inspection:

http://www.SaratogaSkies.com/tmp/ra-drift.gif

The spot data is the instantaneous RA error (with PEC off) measured by
PEMPro. The solid line is a "curve fit" I've done which is simply a
moving average of the instantaneous errors, wherein the "window" of
that moving average is equal to the worm period (382.95 seconds).

Can someone explain why the "RA drift" curve has the odd shape it
does? I would expect it to be roughly monotonically increasing or
decreasing, as polar misalignment and/or atmospheric refraction affect
the apparent RA of the star.

Could this be the reduction gears at work? Or perhaps flexure/sagging
of the camera/focuser? I'm using a 6" refractor with the FT3545
focuser, and an all-threaded coupling between a ST-2000XM camera and
the focuser, and the data was collected at DEC=0 beginning JUST west
of the Meridian and running for roughly 8 worm periods.

More importantly, is this indicative of any issue with the mount? Or
is it just a long-term, slowly varying "drift", that I shouldn't sweat
because it can be easily guided out?

Backlash Measurement Method:

For those interested, here's how I'm measuring DEC Backlash:

1. Preload the DEC gear by moving (at 1x Sidereal) in the Y+ direction
(I use the "move" buttons in PulseGuide for this).
2. Do a calibration in CCDSoft of a specified calibration time.
3. Derive DEC backlash from the measured Y+ and Y- speeds.

Note: Y+ is the first direction that CCDSoft moves in DEC, and then it
moves the same amount in Y-.

I then compute the DEC Backlash as follows:

DEC backlash = (Y+ - Y-) * Tc * Res

where:

o Y+ and Y- are the speeds in pixels/second measured by CCDsoft (px/s)
o Tc is the calibration time in seconds (s)
o Res is the imaging scale produced by my scope/camera combination in
arc-seconds/pixel ("/s)

Is this method valid? If not, why not?

Thanks for any help/advice you folks might be able to offer.

Cheers,
Jim S.


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Re: DEC Backlash and RA "Drift" on AP1200GTO

ayiomamitis
 

--- In ap-gto@yahoogroups.com, "Jim S." <blues_rule_solomon_1999@...> wrote:

Hi Joe,
Jim,


Thanks for the suggestion. I hesitate to do that, though, due to a
rare anomaly which can cause a huge, instantaneous, guide error. Wind
gusts, cosmic ray hits, a momentary fade from a cloud, a satellite
trail ... all of these things can cause a very large instantaneous
error, the damage of which I prefer to limit with that relatively
small maximum move. I certainly see the upside of increasing it though.
I am with you on this one as well ... my MIN is 0.01 sec and my MAX is 0.2 sec .... my
guiding results are stunning.

Anthony.


JS

--- In ap-gto@yahoogroups.com, "JoeMize" <jmize@> wrote:

Jim, change you Max Move from 0.2sec to 2.0sec. 0.2sec limits the
correction to a Maximum drive time of 0.2sec. Changing to 2.0sec
will allow
you to correct longer excursions and Dither moves. I actually have
mine set
to 3.0sec because of the size of my Dither moves...joe :)


Re: DEC Backlash and RA "Drift" on AP1200GTO

Jim S.
 

Hi Richard,

It varies. And CCDSoft doesn't provide those numbers in a convenient
fashion, so I have to go through each 8min exposure to mine them.

Here are a couple of samples from last night. All are 8min imaging
exposures, with 4sec guide exposures. The numbers are in arc-seconds:

1. RAmax = 0.824, RArms = 0.252, DECmax = 0.705, DECrms = 0.303
2. RAmax = 1.337, RArms = 0.323, DECmax = 1.054, DECrms = 0.329
3. RAmax = 1.970, RArms = 0.666, DECmax = 1.967, DECrms = 0.524

These were: (1) the best image of the night (perhaps the best result
I've EVER seen at my site with my gear), (2) a more typical image of
the night, and (3) the worst image of the night, respectively. CCDI
says the FWHMs were 1.94", 3.07", and 4.25", for the actual images,
respectively.

To be fair, the seeing did seem to change over the course of the
night, starting and ending reasonably well but deteriorating for 45min
or so in the middle.

I'm not sure how representative the above numbers truly are. Most
times I bother to calculate out this stuff the DEC rms errors are
actually larger than the RA rms errors (and both are generally larger
than the numbers shown above) which suggests to me that DEC errors are
going uncorrected for one reason or another, and I personally believe
that reason to be DEC backlash.

This was also shooting M81, which is pretty far north, and so the
periodic error is only 1/3 what it would be at the equator, in terms
of "true sky angle".

Cheers,
JS

--- In ap-gto@yahoogroups.com, Richard Seavey <reseavey@...> wrote:

Jim
What are your typical peak and rms guide errors in DEC and RA when your
seeing is in the 2-3 arc-sec range?

Richard