Re: [ap-gto] 1200 mount STV guiding


Jan 30, 2003

 


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

#6574 Jan 30, 2003

Clear Day

Sorry to take up time once again on this issue



I know that by now this might be a beaten issue but last night I took 5 hours to try an experiment with the STV and 1200 mount, with many many different settings all 8 min exposures. FL/ 2700 F/9.1 SBIG 8e



If you are interested in what I have found and would like to try an image or two with these settings you might find you get much better tracking. I would be interested to know if this works on other mounts or it was a fluke on mine last night. I say this because I have had nights that the STV has tracked and given me perfect stars and other nights with the same settings I got elongated stars.



First I ran the mount with my PEM * running and found only drift on the Stars in RA

Dec showed no drift.

I ran the STV with the following settings

STV on guide scope with cords facing down



Mount hand controller speed at .5



STV while calibrating

exposure 7 seconds

mount corrections 15 seconds



STV while tracking

exposure 5 seconds

Y = 0 aggressiveness

X = .4 aggressiveness



ALSO very important, ignore the graph and whatever the error numbers are. I found that I was seeing more error than I wanted yet the stars were round



Not sure but the STV might want to correct the mount more than needed and the 15 second mount calibration time is very important, since when I had it lower no setting worked perfectly

If not these exact setting you may want to think about making the Y axis though very low since that is what wad giving me the trouble



While it was late by the time I decided that this was the best way to image I took 4 images at this setting with round stars.

Was it a fluke? Was it set right for the seeing?



If you would like to try an image or two with these settings and see if it works for you of something closer than you are getting now





Thank you



Mark



* PEM was recorded a few weeks back though when seeing was exceptional one night. Though I ran the STV for the recording with the following settings. This more than likely will have an affect on actual number slightly I think



STV setting while calibrating

exposure 7 seconds

Mount calibrations 5 seconds

STV setting while guiding

exposure 7 seconds

Y = .3 agressiveness

X = .3 aggressiveness











[Non-text portions of this message have been removed]



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

#6575 Jan 30, 2003

In a message dated 1/30/03 5:54:56 AM, aajohnah@... writes:

>Clear Day

>Sorry to take up time once again on this issue

>

>I know that by now this might be a beaten issue but last night I took 5

>hours to try an experiment with the STV and 1200 mount, with many many

>different settings all 8 min exposures. FL/ 2700 F/9.1 SBIG 8e

>

>If you are interested in what I have found and would like to try an image

>or two with these settings you might find you get much better tracking.

>I would be interested to know if this works on other mounts or it was a

>fluke on mine last night. I say this because I have had nights that the

>STV has tracked and given me perfect stars and other nights with the same

>settings I got elongated stars.

>

>First I ran the mount with my PEM * running and found only drift on the

>Stars in RA

>Dec showed no drift.

>I ran the STV with the following settings

>STV on guide scope with cords facing down

>

>Mount hand controller speed at .5

>

>STV while calibrating

>exposure 7 seconds

>mount corrections 15 seconds

>

>STV while tracking

>exposure 5 seconds

>Y = 0 aggressiveness

>X = .4 aggressiveness

>

>ALSO very important, ignore the graph and whatever the error numbers are.

> I found that I was seeing more error than I wanted yet the stars were

>round

>

>Not sure but the STV might want to correct the mount more than needed and

>the 15 second mount calibration time is very important, since when I had

>it lower no setting worked perfectly

>If not these exact setting you may want to think about making the Y axis

>though very low since that is what wad giving me the trouble

>

>While it was late by the time I decided that this was the best way to image

>I took 4 images at this setting with round stars.

>Was it a fluke? Was it set right for the seeing?

>

>If you would like to try an image or two with these settings and see if

>it works for you of something closer than you are getting now

>

>

>Thank you

>

>Mark



MarK:

I don't think you should apologize for posting this information.

There are plenty of STV/AP1200 mount users who are glad to get any

information that might assist them in getting this combination to guide

properly and consistently, myself included.



I think it is also important to post information on your imaging instrument

and guidescope, as their pocal lengths probably figure into the guiding

equation.



Kent Kirkley







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

#6576 Jan 30, 2003

Kirk,



Sorry forgot about the guidescope



On my first go around I was using a Tak FC-60 with focal reducer

FL/380 F/5.3 on a finder bracket

Since the stars were nice but not perfect I figured some flexure had

occurred

At this point I had taken 14 different 8 min images already to get almost

perfect stars



took the scope and finder bracket ( Fc-60 and 70mm bracket) off the main

scope

I also have a FSQ mounted on a top plate on the scope. I re-balanced

everything with it slightly heavier in the east

Used the STV on the FSQ

FL/530 F/5



Stars were perfect so I figure slight flexure on the finder bracket



Main scope is a Mewlon 300 with reducer



Hope that this is more specific and helps in some way



Mark ----- Original Message -----

From: KGKirkley@...>

To: ap-gto@yahoogroups.com>

Sent: Thursday, January 30, 2003 9:02 AM

Subject: Re: [ap-gto] 1200 mount STV guiding





>

> In a message dated 1/30/03 5:54:56 AM, aajohnah@... writes:

>

> >Clear Day

> >Sorry to take up time once again on this issue

> >

> >I know that by now this might be a beaten issue but last night I took 5

> >hours to try an experiment with the STV and 1200 mount, with many many

> >different settings all 8 min exposures. FL/ 2700 F/9.1 SBIG 8e

> >

> >If you are interested in what I have found and would like to try an image

> >or two with these settings you might find you get much better tracking.

> >I would be interested to know if this works on other mounts or it was a

> >fluke on mine last night. I say this because I have had nights that the

> >STV has tracked and given me perfect stars and other nights with the same

> >settings I got elongated stars.

> >

> >First I ran the mount with my PEM * running and found only drift on the

> >Stars in RA

> >Dec showed no drift.

> >I ran the STV with the following settings

> >STV on guide scope with cords facing down

> >

> >Mount hand controller speed at .5

> >

> >STV while calibrating

> >exposure 7 seconds

> >mount corrections 15 seconds

> >

> >STV while tracking

> >exposure 5 seconds

> >Y = 0 aggressiveness

> >X = .4 aggressiveness

> >

> >ALSO very important, ignore the graph and whatever the error numbers

are.

> > I found that I was seeing more error than I wanted yet the stars were

> >round

> >

> >Not sure but the STV might want to correct the mount more than needed and

> >the 15 second mount calibration time is very important, since when I had

> >it lower no setting worked perfectly

> >If not these exact setting you may want to think about making the Y axis

> >though very low since that is what wad giving me the trouble

> >

> >While it was late by the time I decided that this was the best way to

image

> >I took 4 images at this setting with round stars.

> >Was it a fluke? Was it set right for the seeing?

> >

> >If you would like to try an image or two with these settings and see if

> >it works for you of something closer than you are getting now

> >

> >

> >Thank you

> >

> >Mark

>

> MarK:

> I don't think you should apologize for posting this information.

> There are plenty of STV/AP1200 mount users who are glad to get any

> information that might assist them in getting this combination to guide

> properly and consistently, myself included.

>

> I think it is also important to post information on your imaging

instrument

> and guidescope, as their pocal lengths probably figure into the guiding

> equation.

>

> Kent Kirkley

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>



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

#6577 Jan 30, 2003

In a message dated 1/30/03 8:23:42 AM, aajohnah@... writes:

>Kirk,

>

>Sorry forgot about the guidescope

>

>On my first go around I was using a Tak FC-60 with focal reducer

>FL/380 F/5.3 on a finder bracket

>Since the stars were nice but not perfect I figured some flexure had

>occurred

>At this point I had taken 14 different 8 min images already to get almost

>perfect stars

>

>took the scope and finder bracket ( Fc-60 and 70mm bracket) off the main

>scope

>I also have a FSQ mounted on a top plate on the scope. I re-balanced

>everything with it slightly heavier in the east

>Used the STV on the FSQ

>FL/530 F/5

>

>Stars were perfect so I figure slight flexure on the finder bracket

>

>Main scope is a Mewlon 300 with reducer

>

>Hope that this is more specific and helps in some way

>

>Mark



Mark:

Thanks for the info.

As I've posted before, my situation is a little different.

I really want the STV-efinder combination to work with my 1200 & 155 OTA

because the STV-efinder combination is a perfect solution to the guiding

equipment situation.

Small, light, almost no chance of flexure and one less optical tube to

transport.



I've used an ST-4 with various guidescopes since 1996 with excellent results.

The past six months I have had very inconsistent results with the STV, with

guidescopes (AP Traveler), telephoto lens (180mm Nikon ED) and the efinder.

The STV is a far more complicated animal than the St-4 and SBIG's manual is

useless in explaining how to get it to guide accurately and consistently.



Kent Kirkley







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

#6578 Jan 30, 2003

Kent,





Would love to use the E-finder in fact I sold mine three weeks ago

Just does not work well on Focal Lengths over 1800 from what I found and

others I have talked to tell me

Now someone told me just this morning to put a Barlow on the E-finder and it

should work on longer focal lengths. So maybe I will go out and buy another

one g>



After many many hours on this I actually thinking that there is some problem

between the mount and the STV

I am not computer expert but I think that the STV talks a different language

than the mount understands





Mark ----- Original Message -----

From: KGKirkley@...>

To: ap-gto@yahoogroups.com>

Sent: Thursday, January 30, 2003 9:42 AM

Subject: Re: [ap-gto] 1200 mount STV guiding





>

> In a message dated 1/30/03 8:23:42 AM, aajohnah@... writes:

>

> >Kirk,

> >

> >Sorry forgot about the guidescope

> >

> >On my first go around I was using a Tak FC-60 with focal reducer

> >FL/380 F/5.3 on a finder bracket

> >Since the stars were nice but not perfect I figured some flexure had

> >occurred

> >At this point I had taken 14 different 8 min images already to get almost

> >perfect stars

> >

> >took the scope and finder bracket ( Fc-60 and 70mm bracket) off the main

> >scope

> >I also have a FSQ mounted on a top plate on the scope. I re-balanced

> >everything with it slightly heavier in the east

> >Used the STV on the FSQ

> >FL/530 F/5

> >

> >Stars were perfect so I figure slight flexure on the finder bracket

> >

> >Main scope is a Mewlon 300 with reducer

> >

> >Hope that this is more specific and helps in some way

> >

> >Mark

>

> Mark:

> Thanks for the info.

> As I've posted before, my situation is a little different.

> I really want the STV-efinder combination to work with my 1200 & 155 OTA

> because the STV-efinder combination is a perfect solution to the guiding

> equipment situation.

> Small, light, almost no chance of flexure and one less optical tube to

> transport.

>

> I've used an ST-4 with various guidescopes since 1996 with excellent

results.

> The past six months I have had very inconsistent results with the STV,

with

> guidescopes (AP Traveler), telephoto lens (180mm Nikon ED) and the

efinder.

> The STV is a far more complicated animal than the St-4 and SBIG's manual

is

> useless in explaining how to get it to guide accurately and consistently.

>

> Kent Kirkley

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>



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

#6579 Jan 30, 2003

--- In ap-gto@yahoogroups.com, "AA Johnah Fish Estates"

aajohnah@t...> wrote: > Kent,

>

>

> Would love to use the E-finder in fact I sold mine three weeks ago

> Just does not work well on Focal Lengths over 1800 from what I

found and > others I have talked to tell me

> Now someone told me just this morning to put a Barlow on the E-

finder and it > should work on longer focal lengths.



Interesting idea regarding using a barlow to increase the focal

length of an STV efinder. Has it actually been done? How is it done

physically?



Perhaps the other way to think about this is to use a different lens

on the efinder to change the focal length from 100mm to something

longer. Roland, perhaps you can comment?



Jim McMillan



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

#6584 Jan 31, 2003

I have a basic question about guiding, it seems like the STV

overcorrects my mount. The guide star sometimes jumps back and forth

in the box. I turn down the aggressiveness, to maybe 0.3 and it's

better, but not all the way. There must be something wrong with either

the algorithm in the STV, its electrical response, or the mechanics of

correcting the mount.



During calibration, the STV moves the mount for 10 seconds and figures

out how many arcseconds it moves in that time to give arcseconds/second

in four directions. Then when it needs a correction of half an

arcsecond it should be able to "press" the right button for the right

number of milliseconds to achieve that. Why doesn't it that work?

Does a button press of 50 ms really move the mount for 100 ms? In that

case an aggressiveness setting of 0.5 ought to do it. Maybe the mount

is really moving fast during that 50ms, like it's taking up backlash?

Maybe you can't really press the button for such a short amount of time

due to the circuitry in the mount.



I always guide at 0.5x, and am looking forward to the software update

that will let me set guiding rate separate from hand controller button

rate.



By the way, this really only shows up on the STV screen. My stars are

perfectly round on the film, but it bugs me as someone who used to work

in control systems.



--Rick Thurmond

www.rickthurmond.com







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

#6585 Jan 31, 2003

In a message dated 1/31/03 10:15:58 AM, thurmond@... writes:

>I have a basic question about guiding, it seems like the STV

>overcorrects my mount. The guide star sometimes jumps back and forth

>in the box. I turn down the aggressiveness, to maybe 0.3 and it's

>better, but not all the way. There must be something wrong with either

>

>the algorithm in the STV, its electrical response, or the mechanics of

>

>correcting the mount.

>

>During calibration, the STV moves the mount for 10 seconds and figures

>

>out how many arcseconds it moves in that time to give arcseconds/second

>

>in four directions. Then when it needs a correction of half an

>arcsecond it should be able to "press" the right button for the right

>number of milliseconds to achieve that. Why doesn't it that work?

>Does a button press of 50 ms really move the mount for 100 ms? In that

>

>case an aggressiveness setting of 0.5 ought to do it. Maybe the mount

>

>is really moving fast during that 50ms, like it's taking up backlash?

>

>Maybe you can't really press the button for such a short amount of time

>

>due to the circuitry in the mount.

>

>I always guide at 0.5x, and am looking forward to the software update

>that will let me set guiding rate separate from hand controller button

>

>rate.

>

>By the way, this really only shows up on the STV screen. My stars are

>

>perfectly round on the film, but it bugs me as someone who used to work

>

>in control systems.

>

>--Rick Thurmond



Hi Rick:

Join the club.

A lot of people are having trouble with the AP1200 and STV combination,

myself included.

And yes, although I have weird tracking results showing up on the Track

Screen, the apparent inaccuracies don't tend to show up on film.



I've contacted SBIG and they don't have any answers.

Roland at AP now has an STV and is testing it at the WSP in Florida.

He wants to see just what you are asking concerning how long the mount

corrects with a given command.



I'm using the 1200 with my 155, STV with efinder, as this should be a very

cool, simple set-up without extra guidescope, rings, cases, etc.



Kent Kirkley



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

#6586 Jan 31, 2003

Kent,



I have talked with people that are using film and the tracking errors do not

show up on it



However with CCD and a long focal length it shows big time



Mark

----- Original Message -----

From: KGKirkley@...>

To: ap-gto@yahoogroups.com>

Sent: Friday, January 31, 2003 11:30 AM

Subject: Re: [ap-gto] 1200 mount STV guiding





>

> In a message dated 1/31/03 10:15:58 AM, thurmond@... writes:

>

> >I have a basic question about guiding, it seems like the STV

> >overcorrects my mount. The guide star sometimes jumps back and forth

> >in the box. I turn down the aggressiveness, to maybe 0.3 and it's

> >better, but not all the way. There must be something wrong with either

> >

> >the algorithm in the STV, its electrical response, or the mechanics of

> >

> >correcting the mount.

> >

> >During calibration, the STV moves the mount for 10 seconds and figures

> >

> >out how many arcseconds it moves in that time to give arcseconds/second

> >

> >in four directions. Then when it needs a correction of half an

> >arcsecond it should be able to "press" the right button for the right

> >number of milliseconds to achieve that. Why doesn't it that work?

> >Does a button press of 50 ms really move the mount for 100 ms? In that

> >

> >case an aggressiveness setting of 0.5 ought to do it. Maybe the mount

> >

> >is really moving fast during that 50ms, like it's taking up backlash?

> >

> >Maybe you can't really press the button for such a short amount of time

> >

> >due to the circuitry in the mount.

> >

> >I always guide at 0.5x, and am looking forward to the software update

> >that will let me set guiding rate separate from hand controller button

> >

> >rate.

> >

> >By the way, this really only shows up on the STV screen. My stars are

> >

> >perfectly round on the film, but it bugs me as someone who used to work

> >

> >in control systems.

> >

> >--Rick Thurmond

>

> Hi Rick:

> Join the club.

> A lot of people are having trouble with the AP1200 and STV combination,

> myself included.

> And yes, although I have weird tracking results showing up on the Track

> Screen, the apparent inaccuracies don't tend to show up on film.

>

> I've contacted SBIG and they don't have any answers.

> Roland at AP now has an STV and is testing it at the WSP in Florida.

> He wants to see just what you are asking concerning how long the mount

> corrects with a given command.

>

> I'm using the 1200 with my 155, STV with efinder, as this should be a very

> cool, simple set-up without extra guidescope, rings, cases, etc.

>

> Kent Kirkley

>

>

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>







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

#6587 Jan 31, 2003

Hi Rick,



Since you've analyzed control systems, you must know that any system with

feedback can become unstable and will oscillate if the loop delay and

feedback are at/above critical values. This is what happens when

agressiveness is too "high". The value that would be considered "high"

depends on parameters of the mount/guidestar that are going to be different

every time you setup/calibrate.



It is impossible to build a guiding system such as the STV that cannot be

made to oscillate. With the STV, the only real controls you have are the

iteration rate (exposure iteration time) and the overall loop gain

(agressiveness). With experience and some patience, it is possible to

control these so that oscillations do not occur. Although it may take me a

few minutes to adjust my STV, I have always been able to adjust it for good

guiding and no oscillations.



Some basics that have worked for me:

(1) I always calibrate the system before every exposure. Moving the mount to

a different location in the sky can yield different calibrations.

(2) I use 1x guiding (button) setting on my AP1200GTO

(3) I use the longest calibration time that keeps the star on the STV

screen. I think this is 30 seconds with my particular setup. I have found

that using short calibrations is a really bad idea, the STV will then try to

make movements in dec that are unnecessary. This is due (I suppose) to

quantization in the STV calculations.

(4) I use an iteration that give a brightness value on the STV of around

1000 to 2000. Sometimes I have to pick different guidestars since the STV

will pick the brightest one and that is sometimes too bright.

(5) I then set agressiveness to 1.0 and watch the guiding. Always I have to

reduce it but it depends on how long the integration time is. Longer

integrations need more agressive corrections. I just reduce it until the STV

guiding is randomly stepping about the center line (this assumes a good

polar alignment) with less than 1 arcsecond average corrections and less

than 3 or 4 arcseconds instantaneous corrections.



So far, after 2 years of STV use, I've always been able to do this. But

there is no single set of parameters that will work for any guidestar in any

position.



Steve...

----- Original Message -----

From: "Rick Thurmond" thurmond@...>

To: ap-gto@yahoogroups.com>

Sent: Friday, January 31, 2003 11:13 AM

Subject: [ap-gto] 1200 mount STV guiding





> I have a basic question about guiding, it seems like the STV

> overcorrects my mount. The guide star sometimes jumps back and forth

> in the box. I turn down the aggressiveness, to maybe 0.3 and it's

> better, but not all the way. There must be something wrong with either

> the algorithm in the STV, its electrical response, or the mechanics of

> correcting the mount.

>

> During calibration, the STV moves the mount for 10 seconds and figures

> out how many arcseconds it moves in that time to give arcseconds/second

> in four directions. Then when it needs a correction of half an

> arcsecond it should be able to "press" the right button for the right

> number of milliseconds to achieve that. Why doesn't it that work?

> Does a button press of 50 ms really move the mount for 100 ms? In that

> case an aggressiveness setting of 0.5 ought to do it. Maybe the mount

> is really moving fast during that 50ms, like it's taking up backlash?

> Maybe you can't really press the button for such a short amount of time

> due to the circuitry in the mount.

>

> I always guide at 0.5x, and am looking forward to the software update

> that will let me set guiding rate separate from hand controller button

> rate.

>

> By the way, this really only shows up on the STV screen. My stars are

> perfectly round on the film, but it bugs me as someone who used to work

> in control systems.

>

> --Rick Thurmond

> www.rickthurmond.com

>

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>



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

#6588 Jan 31, 2003

Steve,



I find that very interesting

If I go above .4 on my RA or above .1 on my DEC I get to much movement

I also find that 20 seconds works fine for me

I do set my hand controller to .5 though maybe that is the key??????

YET in a single 3 hour time frame of imaging the STV is not constant



A few questions though

Why does the guidestar need to be between 1000 and 2000 brightness

also are you using CCD or film?

And what is your scopes Focal Length and what are you using to guide the STV

with



Thank you



----- Original Message -----

From: "Steve..." s-walters@...>

To: ap-gto@yahoogroups.com>

Sent: Friday, January 31, 2003 11:37 AM

Subject: Re: [ap-gto] 1200 mount STV guiding





> Hi Rick,

>

> Since you've analyzed control systems, you must know that any system with

> feedback can become unstable and will oscillate if the loop delay and

> feedback are at/above critical values. This is what happens when

> agressiveness is too "high". The value that would be considered "high"

> depends on parameters of the mount/guidestar that are going to be

different

> every time you setup/calibrate.

>

> It is impossible to build a guiding system such as the STV that cannot be

> made to oscillate. With the STV, the only real controls you have are the

> iteration rate (exposure iteration time) and the overall loop gain

> (agressiveness). With experience and some patience, it is possible to

> control these so that oscillations do not occur. Although it may take me a

> few minutes to adjust my STV, I have always been able to adjust it for

good

> guiding and no oscillations.

>

> Some basics that have worked for me:

> (1) I always calibrate the system before every exposure. Moving the mount

to

> a different location in the sky can yield different calibrations.

> (2) I use 1x guiding (button) setting on my AP1200GTO

> (3) I use the longest calibration time that keeps the star on the STV

> screen. I think this is 30 seconds with my particular setup. I have found

> that using short calibrations is a really bad idea, the STV will then try

to

> make movements in dec that are unnecessary. This is due (I suppose) to

> quantization in the STV calculations.

> (4) I use an iteration that give a brightness value on the STV of around

> 1000 to 2000. Sometimes I have to pick different guidestars since the STV

> will pick the brightest one and that is sometimes too bright.

> (5) I then set agressiveness to 1.0 and watch the guiding. Always I have

to

> reduce it but it depends on how long the integration time is. Longer

> integrations need more agressive corrections. I just reduce it until the

STV

> guiding is randomly stepping about the center line (this assumes a good

> polar alignment) with less than 1 arcsecond average corrections and less

> than 3 or 4 arcseconds instantaneous corrections.

>

> So far, after 2 years of STV use, I've always been able to do this. But

> there is no single set of parameters that will work for any guidestar in

any

> position.

>

> Steve...

>

> ----- Original Message -----

> From: "Rick Thurmond" thurmond@...>

> To: ap-gto@yahoogroups.com>

> Sent: Friday, January 31, 2003 11:13 AM

> Subject: [ap-gto] 1200 mount STV guiding

>

>

> > I have a basic question about guiding, it seems like the STV

> > overcorrects my mount. The guide star sometimes jumps back and forth

> > in the box. I turn down the aggressiveness, to maybe 0.3 and it's

> > better, but not all the way. There must be something wrong with either

> > the algorithm in the STV, its electrical response, or the mechanics of

> > correcting the mount.

> >

> > During calibration, the STV moves the mount for 10 seconds and figures

> > out how many arcseconds it moves in that time to give arcseconds/second

> > in four directions. Then when it needs a correction of half an

> > arcsecond it should be able to "press" the right button for the right

> > number of milliseconds to achieve that. Why doesn't it that work?

> > Does a button press of 50 ms really move the mount for 100 ms? In that

> > case an aggressiveness setting of 0.5 ought to do it. Maybe the mount

> > is really moving fast during that 50ms, like it's taking up backlash?

> > Maybe you can't really press the button for such a short amount of time

> > due to the circuitry in the mount.

> >

> > I always guide at 0.5x, and am looking forward to the software update

> > that will let me set guiding rate separate from hand controller button

> > rate.

> >

> > By the way, this really only shows up on the STV screen. My stars are

> > perfectly round on the film, but it bugs me as someone who used to work

> > in control systems.

> >

> > --Rick Thurmond

> > www.rickthurmond.com

> >

> >

> > To UNSUBSCRIBE, or for general information on the ap-gto list

> > see groups.yahoo.com/group/ap-gto

> >

> > Your use of Yahoo! Groups is subject to

docs.yahoo.com/info/terms/

> >

> >

>

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>

>







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

#6589 Jan 31, 2003

Mark,



My focal length is 50", I use an offaxis guider on a Tak BRC250.



I believe that setting the controller to 0.5 versus 1.0 rate would tend to

make the problem worse. Which occurs depends on many many things regarding

the particular mount/guiding arrangement you're using. Doing this would

reduce the overall gain in the system but it will just be made up for inside

the STV. In other words, setting the controller to 0.5 means the STV will

issue corrections that are twice as long as if you used 1.0 when

calibrating. Overall this is a bad thing IMO.



Also, I know that some folks like to calibrate at 1 setting and then guide

at a different one. This means that the STV will issue one correction and

the mount will under correct by 50%. Doing this will not eliminate

oscillations in the most general sense, by increasing agressiveness enough,

the mount will still oscillate even at 0.5X.



The selection of a guidestar brightness between 1000 and 2000 is based

simply on experience. What I should have typed is that I select a guidestar

and an integration interval that gives a value in this range. If the star is

too bright, the STV will see a big fat blob and the centroid calculation

will be noisy and produce corrections. Of course, if it's too dim, the STV

will quit guiding should it decrease further due to sky transparency. Also,

the integration interval can be too long, I try for 0.5 seconds but often

will have to use 10 seconds. Ideally, I prefer between 0.5 and 1.0 seconds

provided the brightness is 1000 to 2000. But ya' can't always get that.



I have done both film and CCD imaging with my setup.



Incidentally, along the way, I had lots of problems such as mirror shift,

flexure and polar alignment that "looked like" guiding errors. These can be

very hard to isolate.



For a time, I was using a 200 mm eFinder that I made from a finderscope. I

found that this had two problems for me. One was that my OTA has a small

amount of mirror shift, not much and not often, but it would ruin about 1

image out of every five. But I also realized that the short focal length of

the guidescope means that the STV receives a smaller error signal from the

guidestar centroid which it has to "magnify" to calculate a correction. Even

though this can be done in theory, I found that in practice I got much much

better guiding with the OAG. This meant smaller corrections and with greater

accuracy.



When I have steady seeing (a very rare moment) and my STV is "tuned", I

routinely see average corrections of 0.2 and instantaneous corrections of

0.5 arcseconds. Sometimes this will hold for a minute or so. Then,

turbulence will make it shoot up to 2.0 or even 4.0 arcsecond corrections

for a bit. This is normal operation in the presence of seeing. I was never

able to get such tight guiding using the eFinder.



I know the eFinder is really popular and I really loved its convenience. I'm

actually thinking of getting a cheap CCD to bolt on and use just as a

finder. I am sure the eFinder can be made to guide some systems. But it

never worked well for me.



Steve...



----- Original Message -----

From: "AA Johnah Fish Estates" aajohnah@...>

To: ap-gto@yahoogroups.com>

Sent: Friday, January 31, 2003 11:53 AM

Subject: Re: [ap-gto] 1200 mount STV guiding





> Steve,

>

> I find that very interesting

> If I go above .4 on my RA or above .1 on my DEC I get to much movement

> I also find that 20 seconds works fine for me

> I do set my hand controller to .5 though maybe that is the key??????

> YET in a single 3 hour time frame of imaging the STV is not constant

>

> A few questions though

> Why does the guidestar need to be between 1000 and 2000 brightness

> also are you using CCD or film?

> And what is your scopes Focal Length and what are you using to guide the

STV

> with

>

> Thank you

>

>

> ----- Original Message -----

> From: "Steve..." s-walters@...>

> To: ap-gto@yahoogroups.com>

> Sent: Friday, January 31, 2003 11:37 AM

> Subject: Re: [ap-gto] 1200 mount STV guiding

>

>

> > Hi Rick,

> >

> > Since you've analyzed control systems, you must know that any system

with

> > feedback can become unstable and will oscillate if the loop delay and

> > feedback are at/above critical values. This is what happens when

> > agressiveness is too "high". The value that would be considered "high"

> > depends on parameters of the mount/guidestar that are going to be

> different

> > every time you setup/calibrate.

> >

> > It is impossible to build a guiding system such as the STV that cannot

be

> > made to oscillate. With the STV, the only real controls you have are the

> > iteration rate (exposure iteration time) and the overall loop gain

> > (agressiveness). With experience and some patience, it is possible to

> > control these so that oscillations do not occur. Although it may take me

a

> > few minutes to adjust my STV, I have always been able to adjust it for

> good

> > guiding and no oscillations.

> >

> > Some basics that have worked for me:

> > (1) I always calibrate the system before every exposure. Moving the

mount

> to

> > a different location in the sky can yield different calibrations.

> > (2) I use 1x guiding (button) setting on my AP1200GTO

> > (3) I use the longest calibration time that keeps the star on the STV

> > screen. I think this is 30 seconds with my particular setup. I have

found

> > that using short calibrations is a really bad idea, the STV will then

try

> to

> > make movements in dec that are unnecessary. This is due (I suppose) to

> > quantization in the STV calculations.

> > (4) I use an iteration that give a brightness value on the STV of around

> > 1000 to 2000. Sometimes I have to pick different guidestars since the

STV

> > will pick the brightest one and that is sometimes too bright.

> > (5) I then set agressiveness to 1.0 and watch the guiding. Always I have

> to

> > reduce it but it depends on how long the integration time is. Longer

> > integrations need more agressive corrections. I just reduce it until the

> STV

> > guiding is randomly stepping about the center line (this assumes a good

> > polar alignment) with less than 1 arcsecond average corrections and less

> > than 3 or 4 arcseconds instantaneous corrections.

> >

> > So far, after 2 years of STV use, I've always been able to do this. But

> > there is no single set of parameters that will work for any guidestar in

> any

> > position.

> >

> > Steve...

> >

> > ----- Original Message -----

> > From: "Rick Thurmond" thurmond@...>

> > To: ap-gto@yahoogroups.com>

> > Sent: Friday, January 31, 2003 11:13 AM

> > Subject: [ap-gto] 1200 mount STV guiding

> >

> >

> > > I have a basic question about guiding, it seems like the STV

> > > overcorrects my mount. The guide star sometimes jumps back and forth

> > > in the box. I turn down the aggressiveness, to maybe 0.3 and it's

> > > better, but not all the way. There must be something wrong with

either

> > > the algorithm in the STV, its electrical response, or the mechanics of

> > > correcting the mount.

> > >

> > > During calibration, the STV moves the mount for 10 seconds and figures

> > > out how many arcseconds it moves in that time to give

arcseconds/second

> > > in four directions. Then when it needs a correction of half an

> > > arcsecond it should be able to "press" the right button for the right

> > > number of milliseconds to achieve that. Why doesn't it that work?

> > > Does a button press of 50 ms really move the mount for 100 ms? In

that

> > > case an aggressiveness setting of 0.5 ought to do it. Maybe the mount

> > > is really moving fast during that 50ms, like it's taking up backlash?

> > > Maybe you can't really press the button for such a short amount of

time

> > > due to the circuitry in the mount.

> > >

> > > I always guide at 0.5x, and am looking forward to the software update

> > > that will let me set guiding rate separate from hand controller button

> > > rate.

> > >

> > > By the way, this really only shows up on the STV screen. My stars are

> > > perfectly round on the film, but it bugs me as someone who used to

work

> > > in control systems.

> > >

> > > --Rick Thurmond

> > > www.rickthurmond.com

> > >

> > >

> > > To UNSUBSCRIBE, or for general information on the ap-gto list

> > > see groups.yahoo.com/group/ap-gto

> > >

> > > Your use of Yahoo! Groups is subject to

> docs.yahoo.com/info/terms/

> > >

> > >

> >

> >

> > To UNSUBSCRIBE, or for general information on the ap-gto list

> > see groups.yahoo.com/group/ap-gto

> >

> > Your use of Yahoo! Groups is subject to

docs.yahoo.com/info/terms/

> >

> >

> >

>

>

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>







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

#6590 Jan 31, 2003

Steve,



Thank you

I am using a Mewlon 300 and a FSQ with the STV on it

Who's off axis guider are you using ? I was thinking of going that route,

but then my back focus is increased more than my scope might like

Will try the 1 on the hand controller next



Have only been doing this now for about 10 weeks but it is frustrating with

the STV to say the least



Thank you for all your input



Mark ----- Original Message -----

From: "Steve..." s-walters@...>

To: ap-gto@yahoogroups.com>

Sent: Friday, January 31, 2003 1:09 PM

Subject: Re: [ap-gto] 1200 mount STV guiding





> Mark,

>

> My focal length is 50", I use an offaxis guider on a Tak BRC250.

>

> I believe that setting the controller to 0.5 versus 1.0 rate would tend to

> make the problem worse. Which occurs depends on many many things regarding

> the particular mount/guiding arrangement you're using. Doing this would

> reduce the overall gain in the system but it will just be made up for

inside

> the STV. In other words, setting the controller to 0.5 means the STV will

> issue corrections that are twice as long as if you used 1.0 when

> calibrating. Overall this is a bad thing IMO.

>

> Also, I know that some folks like to calibrate at 1 setting and then guide

> at a different one. This means that the STV will issue one correction and

> the mount will under correct by 50%. Doing this will not eliminate

> oscillations in the most general sense, by increasing agressiveness

enough,

> the mount will still oscillate even at 0.5X.

>

> The selection of a guidestar brightness between 1000 and 2000 is based

> simply on experience. What I should have typed is that I select a

guidestar

> and an integration interval that gives a value in this range. If the star

is

> too bright, the STV will see a big fat blob and the centroid calculation

> will be noisy and produce corrections. Of course, if it's too dim, the STV

> will quit guiding should it decrease further due to sky transparency.

Also,

> the integration interval can be too long, I try for 0.5 seconds but often

> will have to use 10 seconds. Ideally, I prefer between 0.5 and 1.0 seconds

> provided the brightness is 1000 to 2000. But ya' can't always get that.

>

> I have done both film and CCD imaging with my setup.

>

> Incidentally, along the way, I had lots of problems such as mirror shift,

> flexure and polar alignment that "looked like" guiding errors. These can

be

> very hard to isolate.

>

> For a time, I was using a 200 mm eFinder that I made from a finderscope. I

> found that this had two problems for me. One was that my OTA has a small

> amount of mirror shift, not much and not often, but it would ruin about 1

> image out of every five. But I also realized that the short focal length

of

> the guidescope means that the STV receives a smaller error signal from the

> guidestar centroid which it has to "magnify" to calculate a correction.

Even

> though this can be done in theory, I found that in practice I got much

much

> better guiding with the OAG. This meant smaller corrections and with

greater

> accuracy.

>

> When I have steady seeing (a very rare moment) and my STV is "tuned", I

> routinely see average corrections of 0.2 and instantaneous corrections of

> 0.5 arcseconds. Sometimes this will hold for a minute or so. Then,

> turbulence will make it shoot up to 2.0 or even 4.0 arcsecond corrections

> for a bit. This is normal operation in the presence of seeing. I was never

> able to get such tight guiding using the eFinder.

>

> I know the eFinder is really popular and I really loved its convenience.

I'm

> actually thinking of getting a cheap CCD to bolt on and use just as a

> finder. I am sure the eFinder can be made to guide some systems. But it

> never worked well for me.

>

> Steve...

>

>

> ----- Original Message -----

> From: "AA Johnah Fish Estates" aajohnah@...>

> To: ap-gto@yahoogroups.com>

> Sent: Friday, January 31, 2003 11:53 AM

> Subject: Re: [ap-gto] 1200 mount STV guiding

>

>

> > Steve,

> >

> > I find that very interesting

> > If I go above .4 on my RA or above .1 on my DEC I get to much movement

> > I also find that 20 seconds works fine for me

> > I do set my hand controller to .5 though maybe that is the key??????

> > YET in a single 3 hour time frame of imaging the STV is not constant

> >

> > A few questions though

> > Why does the guidestar need to be between 1000 and 2000 brightness

> > also are you using CCD or film?

> > And what is your scopes Focal Length and what are you using to guide the

> STV

> > with

> >

> > Thank you

> >

> >

> > ----- Original Message -----

> > From: "Steve..." s-walters@...>

> > To: ap-gto@yahoogroups.com>

> > Sent: Friday, January 31, 2003 11:37 AM

> > Subject: Re: [ap-gto] 1200 mount STV guiding

> >

> >

> > > Hi Rick,

> > >

> > > Since you've analyzed control systems, you must know that any system

> with

> > > feedback can become unstable and will oscillate if the loop delay and

> > > feedback are at/above critical values. This is what happens when

> > > agressiveness is too "high". The value that would be considered "high"

> > > depends on parameters of the mount/guidestar that are going to be

> > different

> > > every time you setup/calibrate.

> > >

> > > It is impossible to build a guiding system such as the STV that cannot

> be

> > > made to oscillate. With the STV, the only real controls you have are

the

> > > iteration rate (exposure iteration time) and the overall loop gain

> > > (agressiveness). With experience and some patience, it is possible to

> > > control these so that oscillations do not occur. Although it may take

me

> a

> > > few minutes to adjust my STV, I have always been able to adjust it for

> > good

> > > guiding and no oscillations.

> > >

> > > Some basics that have worked for me:

> > > (1) I always calibrate the system before every exposure. Moving the

> mount

> > to

> > > a different location in the sky can yield different calibrations.

> > > (2) I use 1x guiding (button) setting on my AP1200GTO

> > > (3) I use the longest calibration time that keeps the star on the STV

> > > screen. I think this is 30 seconds with my particular setup. I have

> found

> > > that using short calibrations is a really bad idea, the STV will then

> try

> > to

> > > make movements in dec that are unnecessary. This is due (I suppose) to

> > > quantization in the STV calculations.

> > > (4) I use an iteration that give a brightness value on the STV of

around

> > > 1000 to 2000. Sometimes I have to pick different guidestars since the

> STV

> > > will pick the brightest one and that is sometimes too bright.

> > > (5) I then set agressiveness to 1.0 and watch the guiding. Always I

have

> > to

> > > reduce it but it depends on how long the integration time is. Longer

> > > integrations need more agressive corrections. I just reduce it until

the

> > STV

> > > guiding is randomly stepping about the center line (this assumes a

good

> > > polar alignment) with less than 1 arcsecond average corrections and

less

> > > than 3 or 4 arcseconds instantaneous corrections.

> > >

> > > So far, after 2 years of STV use, I've always been able to do this.

But

> > > there is no single set of parameters that will work for any guidestar

in

> > any

> > > position.

> > >

> > > Steve...

> > >

> > > ----- Original Message -----

> > > From: "Rick Thurmond" thurmond@...>

> > > To: ap-gto@yahoogroups.com>

> > > Sent: Friday, January 31, 2003 11:13 AM

> > > Subject: [ap-gto] 1200 mount STV guiding

> > >

> > >

> > > > I have a basic question about guiding, it seems like the STV

> > > > overcorrects my mount. The guide star sometimes jumps back and

forth

> > > > in the box. I turn down the aggressiveness, to maybe 0.3 and it's

> > > > better, but not all the way. There must be something wrong with

> either

> > > > the algorithm in the STV, its electrical response, or the mechanics

of

> > > > correcting the mount.

> > > >

> > > > During calibration, the STV moves the mount for 10 seconds and

figures

> > > > out how many arcseconds it moves in that time to give

> arcseconds/second

> > > > in four directions. Then when it needs a correction of half an

> > > > arcsecond it should be able to "press" the right button for the

right

> > > > number of milliseconds to achieve that. Why doesn't it that work?

> > > > Does a button press of 50 ms really move the mount for 100 ms? In

> that

> > > > case an aggressiveness setting of 0.5 ought to do it. Maybe the

mount

> > > > is really moving fast during that 50ms, like it's taking up

backlash?

> > > > Maybe you can't really press the button for such a short amount of

> time

> > > > due to the circuitry in the mount.

> > > >

> > > > I always guide at 0.5x, and am looking forward to the software

update

> > > > that will let me set guiding rate separate from hand controller

button

> > > > rate.

> > > >

> > > > By the way, this really only shows up on the STV screen. My stars

are

> > > > perfectly round on the film, but it bugs me as someone who used to

> work

> > > > in control systems.

> > > >

> > > > --Rick Thurmond

> > > > www.rickthurmond.com

> > > >

> > > >

> > > > To UNSUBSCRIBE, or for general information on the ap-gto list

> > > > see groups.yahoo.com/group/ap-gto

> > > >

> > > > Your use of Yahoo! Groups is subject to

> > docs.yahoo.com/info/terms/

> > > >

> > > >

> > >

> > >

> > > To UNSUBSCRIBE, or for general information on the ap-gto list

> > > see groups.yahoo.com/group/ap-gto

> > >

> > > Your use of Yahoo! Groups is subject to

> docs.yahoo.com/info/terms/

> > >

> > >

> > >

> >

> >

> >

> > To UNSUBSCRIBE, or for general information on the ap-gto list

> > see groups.yahoo.com/group/ap-gto

> >

> > Your use of Yahoo! Groups is subject to

docs.yahoo.com/info/terms/

> >

> >

>

>

> To UNSUBSCRIBE, or for general information on the ap-gto list

> see groups.yahoo.com/group/ap-gto

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

>

>







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

#6591 Jan 31, 2003

Mark,



I'm using the Mitsuboshi OAG and 6x9 camera from Hutech. Backfocus is also a

bit short with the Tak BRC (106 mm I think) but Mitsuboshi has a setup that

puts the camera at the right position. The construction is very precise. Of

course, using an OAG is a royal pain in the a** but I have found a way that

works well for me that takes advantage of the AP1200GTO. I simply use "The

Sky" and overlay a Field-Of-View circle that is the diameter of the OAG

offset. I can then place a guidestar right on the circle by moving the mount

around and can also estimate the position to put the OAG at. I simply rotate

the OAG near this position and watch the STV display until the guidestar

shows up. If the guidestar is dim, it will try my patience a bit but I no

longer even remove the STV camera head when positioning it. It's firmly

bolted onto the OAG guiding port and is never removed. I replaced the

knurled screws with allen head screws and leave it locked down, the STV

camera head and OAG are mated for life.



My friend who had glitches with his STV was driven half crazy by it (some

would say entirely crazy but I think he was that way to start with). It does

have a learning curve but you'll surely get past that.



Steve...

----- Original Message -----

From: "AA Johnah Fish Estates" aajohnah@...>

To: ap-gto@yahoogroups.com>

Sent: Friday, January 31, 2003 1:28 PM

Subject: Re: [ap-gto] 1200 mount STV guiding





> Steve,

>

> Thank you

> I am using a Mewlon 300 and a FSQ with the STV on it

> Who's off axis guider are you using ? I was thinking of going that route,

> but then my back focus is increased more than my scope might like

> Will try the 1 on the hand controller next

>

> Have only been doing this now for about 10 weeks but it is frustrating

with

> the STV to say the least

>

> Thank you for all your input

>

> Mark

>



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

#6592 Jan 31, 2003

In a message dated 1/31/2003 10:16:00 AM Central Standard Time,

thurmond@... writes:



> Maybe the mount

> is really moving fast during that 50ms, like it's taking up backlash?

> Maybe you can't really press the button for such a short amount of time

> due to the circuitry in the mount.

>



The mount will respond to 8 millisecond button pushes. 8 msec @1x= 0.12 arc.

If you have your settings set for minimum on-time of 100 msec, then the STV

will send out a minimum pulse equal to 1.5 arc sec. Keep the min on-time as

low as possible. Also, make sure that Dec backlash setting is ZERO during

guiding, otherwise you may get overshoot in Dec. (RA backlash setting has no

effect in guiding.)



Roland Christen





[Non-text portions of this message have been removed]


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