Counter weight up slew vs. continuing past the meridian, any real differences?


skester@...
 

I've seen many comments about the ability of AP mounts to slew to a counterweight up position with the scope on the east side, so that you can avoid the flip and continue west.  Assuming I want to track the target from -3hrs to +3hrs of the meridian, how if at all is this different to starting with a normal slew with the scope on the west side, and ending in the counter weight up position (assuming clearance of course)?  Earlier this week it was mentioned that due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety slew thus making very small adjustments quit slow.  It would seem a solution would be to just reverse the process and end rather than start counter weight up.  Am I missing something here?


Geof Lewis
 

Hi,
IMHO there is no difference. I don't use APCC/APMM, but just use SGP and set any required meridian delay in the V2 driver. For me the decision is determined by what the starting position of my target is and how long I want to image it. So, if I have a target within 3 hours east of the meridian and want to image it for say 8 hours, then I'll set the meridian delay such that I start CW up and finish CW down. However, if the target is 5 hours east of the meridian and I want to image for 8 hours, then the reverse is true and I'll start CW down and finish CW up. I've never encountered any issues with slow slews, or back and forth sides, as plate solving runs. Of course, I do need to check that I won't get any pier crashes and I find it easier to monitor that with CW up at the start, knowing that if I'm good there then very likely to be good after all the way through and past the meridian.
Best regards,

Geof


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of skester@... <skester@...>
Sent: 13 March 2021 17:02
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?
 
I've seen many comments about the ability of AP mounts to slew to a counterweight up position with the scope on the east side, so that you can avoid the flip and continue west.  Assuming I want to track the target from -3hrs to +3hrs of the meridian, how if at all is this different to starting with a normal slew with the scope on the west side, and ending in the counter weight up position (assuming clearance of course)?  Earlier this week it was mentioned that due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety slew thus making very small adjustments quit slow.  It would seem a solution would be to just reverse the process and end rather than start counter weight up.  Am I missing something here?


Ray Gralak
 

Earlier this week it was mentioned that
due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety
slew thus making very small adjustments quit slow.
APCC has a variety of meridian limit configuration settings. When setup appropriately, counterweight-up slews within APCC's meridian limits will not do safety slews, and thus do not result in extra time in SGPro. However, if SGPro issues a move outside of the meridian limits then a pier flip will occur.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of skester@gmail.com
Sent: Saturday, March 13, 2021 9:02 AM
To: main@ap-gto.groups.io
Subject: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

I've seen many comments about the ability of AP mounts to slew to a counterweight up position with the scope on
the east side, so that you can avoid the flip and continue west. Assuming I want to track the target from -3hrs to
+3hrs of the meridian, how if at all is this different to starting with a normal slew with the scope on the west side, and
ending in the counter weight up position (assuming clearance of course)? Earlier this week it was mentioned that
due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety
slew thus making very small adjustments quit slow. It would seem a solution would be to just reverse the process
and end rather than start counter weight up. Am I missing something here?


Luca Marinelli
 

Ray,

How would I set up APCC so that slews within the East limits with CW up from SGP do not invoke safety slews? Is it in the APCC manual?

Thanks,

Luca

On Mar 13, 2021, at 12:19 PM, Ray Gralak via groups.io <iogroups=siriusimaging.com@groups.io> wrote:



Earlier this week it was mentioned that
due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety
slew thus making very small adjustments quit slow.
APCC has a variety of meridian limit configuration settings. When setup appropriately, counterweight-up slews within APCC's meridian limits will not do safety slews, and thus do not result in extra time in SGPro. However, if SGPro issues a move outside of the meridian limits then a pier flip will occur.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of skester@gmail.com
Sent: Saturday, March 13, 2021 9:02 AM
To: main@ap-gto.groups.io
Subject: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

I've seen many comments about the ability of AP mounts to slew to a counterweight up position with the scope on
the east side, so that you can avoid the flip and continue west. Assuming I want to track the target from -3hrs to
+3hrs of the meridian, how if at all is this different to starting with a normal slew with the scope on the west side, and
ending in the counter weight up position (assuming clearance of course)? Earlier this week it was mentioned that
due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety
slew thus making very small adjustments quit slow. It would seem a solution would be to just reverse the process
and end rather than start counter weight up. Am I missing something here?





Ray Gralak
 

Luca,

How would I set up APCC so that slews within the East limits with CW up from SGP do not invoke safety slews?
If the SGPro move is 0.5 degrees or less in Declination then there will be no safety slew.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Luca Marinelli
Sent: Saturday, March 13, 2021 2:09 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

Ray,

How would I set up APCC so that slews within the East limits with CW up from SGP do not invoke safety slews? Is
it in the APCC manual?

Thanks,

Luca

On Mar 13, 2021, at 12:19 PM, Ray Gralak via groups.io <iogroups=siriusimaging.com@groups.io> wrote:



Earlier this week it was mentioned that
due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety
slew thus making very small adjustments quit slow.
APCC has a variety of meridian limit configuration settings. When setup appropriately, counterweight-up slews
within APCC's meridian limits will not do safety slews, and thus do not result in extra time in SGPro. However, if
SGPro issues a move outside of the meridian limits then a pier flip will occur.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of skester@gmail.com
Sent: Saturday, March 13, 2021 9:02 AM
To: main@ap-gto.groups.io
Subject: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

I've seen many comments about the ability of AP mounts to slew to a counterweight up position with the scope
on
the east side, so that you can avoid the flip and continue west. Assuming I want to track the target from -3hrs to
+3hrs of the meridian, how if at all is this different to starting with a normal slew with the scope on the west side,
and
ending in the counter weight up position (assuming clearance of course)? Earlier this week it was mentioned that
due to how SGP commands the mount during a plate solve/center, starting counter weight up invokes the safety
slew thus making very small adjustments quit slow. It would seem a solution would be to just reverse the
process
and end rather than start counter weight up. Am I missing something here?







Luca Marinelli
 

On Sat, Mar 13, 2021 at 05:29 PM, Ray Gralak wrote:
Luca,

How would I set up APCC so that slews within the East limits with CW up from SGP do not invoke safety slews?
If the SGPro move is 0.5 degrees or less in Declination then there will be no safety slew.

-Ray


Thanks, Ray. So if I read your statement correctly, there is no special setting in APCC that will avoid safety slews within the meridian limits but if the slew issued is close enough in Dec, then APCC will simply nudge the mount to the right place, without going back to CW down first.

It's not a big deal either way; we are only talking about two or three slews per target. But then again, neither is a Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.

Luca


Ray Gralak
 

Hi Luca,

It's not a big deal either way; we are only talking about two or three slews per target. But then again, neither is a
Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.
Can you clarify? Are you saying that SGPro needs to slew two or three times in the course of platesolving a new target, and in the process of doing this APCC is doing a pier flip and multiple safe slews for the *same* target?

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Luca Marinelli
Sent: Sunday, March 14, 2021 6:56 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

On Sat, Mar 13, 2021 at 05:29 PM, Ray Gralak wrote:


Luca,



How would I set up APCC so that slews within the East limits with CW up from SGP do not invoke
safety slews?

If the SGPro move is 0.5 degrees or less in Declination then there will be no safety slew.

-Ray




Thanks, Ray. So if I read your statement correctly, there is no special setting in APCC that will avoid safety slews
within the meridian limits but if the slew issued is close enough in Dec, then APCC will simply nudge the mount to
the right place, without going back to CW down first.

It's not a big deal either way; we are only talking about two or three slews per target. But then again, neither is a
Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.

Luca


Michael 'Mikey' Mangieri
 

SGP sometimes needs three slews to get on target. I have found in the past that my scope did in fact due three meridian flips when trying to plate solve.

On Mar 14, 2021, at 10:07 AM, Ray Gralak <iogroups@siriusimaging.com> wrote:

Hi Luca,

It's not a big deal either way; we are only talking about two or three slews per target. But then again, neither is a
Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.
Can you clarify? Are you saying that SGPro needs to slew two or three times in the course of platesolving a new target, and in the process of doing this APCC is doing a pier flip and multiple safe slews for the *same* target?

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Luca Marinelli
Sent: Sunday, March 14, 2021 6:56 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

On Sat, Mar 13, 2021 at 05:29 PM, Ray Gralak wrote:


Luca,



How would I set up APCC so that slews within the East limits with CW up from SGP do not invoke
safety slews?

If the SGPro move is 0.5 degrees or less in Declination then there will be no safety slew.

-Ray




Thanks, Ray. So if I read your statement correctly, there is no special setting in APCC that will avoid safety slews
within the meridian limits but if the slew issued is close enough in Dec, then APCC will simply nudge the mount to
the right place, without going back to CW down first.

It's not a big deal either way; we are only talking about two or three slews per target. But then again, neither is a
Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.

Luca





Marcelo Figueroa
 


I just let SGP handle the meridian flips on its own (I have these settings disabled in APCC, too lazy to set them up right), it works perfect every time with a Mach2 on a single attempt.
 
The only time it has failed was in a cloud attack that prevented SGP from doing its plate solving.


Luca Marinelli
 
Edited

On Sun, Mar 14, 2021 at 10:07 AM, Ray Gralak wrote:
Hi Luca,

It's not a big deal either way; we are only talking about two or three slews per target. But then again, neither is a
Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.
Can you clarify? Are you saying that SGPro needs to slew two or three times in the course of platesolving a new target, and in the process of doing this APCC is doing a pier flip and multiple safe slews for the *same* target?

-Ray

When I set up a target in SGP, I'll enter RA and DEC coordinates for the center of the image, as well as rotation angle of the frame. I start the evening with a "closed loop slew" to use TSX terminology to the target. The precision I require for the centering process is 30 points maximum error, which translates to roughly 20 arc-sec. If I am not running a model on the Mach2 or the AP1100, the "closed loop slew"  to the target will usually take 2-3 slews. The first gets you within half a degree to a degree of the target, depending on its position in the sky, and the second one gets you perfectly there or almost. If I am using a model, depending on where the target is in the sky, it will take 1-2 slews to get there.

If I allow APCC to run counterweight up slews within East limits and if the target is within East limits, when SGP issues the first slew command to center the target, the mount will go in a CW up position with the scope on the East side pointing East. When I have been next to the mount I have observed that the next slew or two to refine the position of the mount and meet the required precision for centering the frame will be safety slews.

The same holds for meridian flips. After issuing the slew command that triggers the meridian flip, SGP will run a platosolve task to confirm the correct position of the target. Typically, it will then issue a second and rarely a third slew to center the target with 20 arc-sec precision. The slews after a meridan flip will not be safety slews because they are CW down.

My observation was that in theory starting from a CW up position saves imaging time, in practice I have found the opposite because safety slews take longer. That's all I was saying. Again, this is an entirely minor difference and overall minute contribution to overhead compared to time spent focusing, dithering, saving files, etc. If you relax the precision requirement, obviously it will take fewer slew to get the frame centered. I image targets over the course of several months and require this precision so I don't have to trim the edge of the frames excessively.

If there is a better way to set up APCC to reduce this time overhead, I am always looking for ways to improve how the software works together.

Luca


Ray Gralak
 

Hi Luca,

My observation was that in theory starting from a CW up position saves imaging time, in practice I have found the
opposite because safety slews take longer.
First, the primary purpose of starting or ending in a counterweight-up position is not necessarily to save time but to be able to use the same guide star across the meridian. If you are using an off-axis autoguider without a camera rotator you may not get a good guide star (or any guide star) after a pier flip. But, if you have a camera rotator, using a separate guide scope, or unguided, there is not much advantage to counterweight-up imaging.

The precision I
require for the centering process is 30 points maximum error, which translates to roughly 20 arc-sec. If I am not
running a model on the Mach2 or the AP1100, the "closed loop slew" (to use TSX terminology) to the target will
usually take 2-3 slews. the first gets you with a degree, usually, and the second one gets you perfectly there or
If you are using an APCC pointing model, the declination pointing error should not be much less than the +/- 1/2 degree declination tolerance before a safety slew. If it is, then you probably should redo the pointing model, including adding more counterweight-up points.

If I allow APCC to run counterweight up slews within East limits and if the target is within East limits, when SGP
issues the first slew command to center the target, the mount will go in a CW up position with the scope on the East
side pointing East. When I have been next to the mount I have observed that the next slew or two to refine the
position of the mount and meet the required precision for centering the frame will be safety slews.
Again, a better pointing model should prevent safety slews, as exceeding the +/- 1/2 degree declination tolerance is unlikely unless SGPro is purposely moving the mount away from the target.

-Ray


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Luca Marinelli
Sent: Sunday, March 14, 2021 3:17 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Counter weight up slew vs. continuing past the meridian, any real differences?

On Sun, Mar 14, 2021 at 10:07 AM, Ray Gralak wrote:


Hi Luca,



It's not a big deal either way; we are only talking about two or three slews per target. But then again,
neither is a
Meridian flip, which also take a couple of slews per target for plate solving. That was my original point.

Can you clarify? Are you saying that SGPro needs to slew two or three times in the course of platesolving a
new target, and in the process of doing this APCC is doing a pier flip and multiple safe slews for the *same* target?

-Ray


When I set up a target in SGP, I'll enter RA and DEC coordinates for the center of the image, as well as rotation
angle of the frame. I start the evening with a "closed loop slew" to use TSX terminology to the target. The precision I
require for the centering process is 30 points maximum error, which translates to roughly 20 arc-sec. If I am not
running a model on the Mach2 or the AP1100, the "closed loop slew" (to use TSX terminology) to the target will
usually take 2-3 slews. the first gets you with a degree, usually, and the second one gets you perfectly there or
almost. If I am using a model, depending on where the target is in the sky, it will take 1-2 slews to get there.

If I allow APCC to run counterweight up slews within East limits and if the target is within East limits, when SGP
issues the first slew command to center the target, the mount will go in a CW up position with the scope on the East
side pointing East. When I have been next to the mount I have observed that the next slew or two to refine the
position of the mount and meet the required precision for centering the frame will be safety slews.

The same holds for meridian flips. After issuing the slew command that triggers the meridian flip, SGP will run a
platosolve task to confirm the correct position of the target. Typically, it will then issue a second and rarely a third
slew to center the target with 20 arc-sec precision. The slews after a meridan flip will not be safety slews because
they are CW down.

My observation was that in theory starting from a CW up position saves imaging time, in practice I have found the
opposite because safety slews take longer. That's all I was saying. Again, this is an entirely minor difference and
overall minute contribution to overhead compared to time spent focusing, dithering, saving files, etc. If you relax the
precision requirement, obviously it will take fewer slew to get the frame centered. I image targets over the course of
several months and require this precision so I don't have to trim the edge of the frames excessively.

If there is a better way to set up APCC to reduce this time overhead, I am always looking for ways to improve how
the software works together.

Luca