¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. ServoCAT
  2. Topics

Settings for use of AutoGUIDE

 
Edited

Here comes a description of the hardware and settings i have used to successfully Autoguide with my ServoCat driven Starstructure:
?
?
1. Hardware:
- I use a 50mm /180mm focal length Guidescope (Omegon Guidescope Modul-Finder) and it has worked just fine, of course a larger guidescope? ? ? ?would be better as long as it does not flex.
- ST4 cable, if you can find the right length RJ12 6P6C in a local store it will be much cheaper, at least here 3 meters was in stock.
- Guidecamera like the ZWO ASI 120MM Mini (comes with a 2 meter ST4 and USB cable). Touptek or a similar brand could have a cheaper alternative.
?
The above hardware was selected because it was the lowest cost alternative that i could find which did not require any modification to my telescope.
?
1. Software?
- PHD2
- Camera driver
?
After mounting the Guidescope, connecting the ST4 cable from the Guidecamera to the back of the ServoCAT to the AUX/AG port and connecting the USB cable from the Guidecamera to your PC you are ready to go from a hardware standpoint except aligning the guidescope with the main scope.
?
In ServoCAT sky i use 6 arc seconds per second for the GUIDE 2 value (0.40 x Sidereal) and in the PHD2 Profile Wizard i use 0.20x Sidereal. The reason is beacuse the measured guidespeed for my scope is lower than the speed entered in ServoCAT Sky due to friction.
?
When you first start PHD2 and follow the Profile Wizard, choose "On camera" when selecting mount.
The instructions will end with creating a dark library where it asks you to cover the scope, after that the setup is done!
?
Click on the brain icon and choose Algorithms at the top of the window. Change the declination Algorithm to "Hysteresis" like is already selected on RA and make sure dec mode is on auto. In our case RA is AZ and DEC is ALT.
?
When aligning the Guidescope to the main scope you could align the guidescope off center with regards to the main scope as long as you know where in the guidescope field of view the main scope is pointing, and as long as the guidestar you choose when imaging is as close to that point as possible since the field will appear to rotate around the guidestar.?
?
Make sure that the "Guide" button on the ServoCAT handpad is selected or PHD2 will not be able to send pulse commands.
?
Slew the scope to 30 -40 degrees above the horizon in altitude and in azimuth around 90 degrees has worked well for me, as long as you don't point directly north or south. Take out the backlash in Altitude before performing the PHD2 calibration.
?
At the bottom of the window hit Guide, now the calibration will start. PHD2 will move the mount West, East, North, and South in order to understand how the mount behaves. When the calibration is done the scope will begin guiding, this is when i stop guiding and slew to my target to begin capture.
?
You don't have to recalibrate if you change target. PHD2 will prompt you to enter declination when starting to guide (ALT for us). If using a mount driver like the Meade Generic PHD2 will automatically know where the scope is pointing.
?
If you check "Auto restore calibration" in PHD2 settings you don't have to recalibrate the next imaging session, and as long as the scope behaviour has not changed like if the bearings have been lubricated or become dirty it should work.
?
In my experience Multi-star guiding gives much better results than guiding on 1 star, it averages the star movement on up to 12 stars (if i remember correctly). There is a box in PHD2 settings to check "Use multiple stars". However you don't get to choose the main star so if it is very far from where your scope is pointing the object will move out of the main field of view faster, however it has not been a major issue for me.
?
I recommend running the Guide assistant when you have begun guiding on the nights target. It will suggest improvements and you only have to click on "apply". The standard settings should work well though! I uncheck "measure declination backlash" since i have not found a reason to measure it.
?
It's important that the guidescope is firmly mounted since just a few microns of flexure is capable of throwing of the guidestar by 6 arc seconds, several star diameters, a human hair is 50 microns thick.
?
The best i have achieved so far with my Starstructure is 0.69" arc seconds total RMS during a 2.5 minute period, something i never even thought was possible with a dob.
?
Seeing plays a huge roll, so even if everything is "perfect" you could get 2 arc second RMS guiding just beacuse of rough seeing.
I have found that Multi-star guiding does a lot to mitigate this. I think my seeing is below avarege compared to global standards.
?
1.5 arc seconds and below is what i find acceptable. It's easy to get hung up on the numbers, if the results are good forget the numbers!
?
Clear skies!
Gabriel
?
 

Hi Gabriel,
Thank you so much to have described in detail how to autoguide !
It will be very usefull if I decided to autoguide in future !
Thanks
Rapha?l
 

Hi Raphael,
?
Your welcome
?
Thank you and clear skies!
?
/Gabriel
 

Just for fun this evening i tried using Easytrack on it's own without any DSC just to see if autoguiding is able to compensate for such basic tracking. I have marks on my scope so i manually can point it at roughly 0 az and 63 alt, so with SPEED 2 i pressed the CCW button on the handpad, switched on the ServoCAT and let go of the button when the yellow SPM light turned on = scope is tracking.
?
Here is a 60 second sub (crop of the very center), i just slewed the scope randomly to the north east at about 50 degrees in altitude. In actual capture i would of course never use that kind of exposure time since my scope is sky fog limited after only 20 seconds.
?
?
Here is the graph in PHD2:
?
?
Pherhaps hard to see but total RMS is 1.28" arc seconds, not bad for only using Easytrack if you ask me.
?
So in other words, the 2-star alignment is less critical when using autoguiding.
?
/ Gabriel
?
?
 

Gabriel,

HATS OFF TO YOU SIR!?

Super exercise ... and definitive results. Great job.?

Gary Myers
StellarCAT



------ Original Message ------
From "Gabriel Wiklund via groups.io" <gabriel.wiklundholeshot@...>
Date 2/17/2025 5:53:55 PM
Subject Re: [ServoCAT] Settings for use of AutoGUIDE

Just for fun this evening i tried using Easytrack on it's own without any DSC just to see if autoguiding is able to compensate for such basic tracking. I have marks on my scope so i manually can point it at roughly 0 az and 63 alt, so with SPEED 2 i pressed the CCW button on the handpad, switched on the ServoCAT and let go of the button when the yellow SPM light turned on = scope is tracking.
?
Here is a 60 second sub (crop of the very center), i just slewed the scope randomly to the north east at about 50 degrees in altitude. In actual capture i would of course never use that kind of exposure time since my scope is sky fog limited after only 20 seconds.
?
?
Here is the graph in PHD2:
?
?
Pherhaps hard to see but total RMS is 1.28" arc seconds, not bad for only using Easytrack if you ask me.
?
So in other words, the 2-star alignment is less critical when using autoguiding.
?
/ Gabriel
?
?
 

Thank you Gary, much appreciated!
?
/Gabriel
 

I will add one note to this info - and thanks Gabriel - MUCH more than I was asking for but very much appreciated.?

That note is that using a standard refractor as a guide scope (i.e. a guide scope) if you position the camera such that the name on the back of the camera is upside down but horizontal, you should have proper arrangements that correlate to movement - i.e. east moves the image east, north moves it up.?

I found this to be helpful if for any reason I wanted to use the guide image to move around the sky. (that orientation I believe is universal - name upside down - but I can't say that for a fact, it just makes sense to me since on my SVBony guide camera, the 305 Pro, it is as noted.)?

When you do this the chip is horizontal and by making it upside down you basically counter the effective 'mirror image' that the lens produces.?

g.




------ Original Message ------
From "Gabriel Wiklund via groups.io" <gabriel.wiklundholeshot@...>
Date 2/17/2025 1:11:52 PM
Subject [ServoCAT] Settings for use of AutoGUIDE

[Edited Message Follows]

Here comes a description of the hardware and settings i have used to successfully Autoguide with my ServoCat driven Starstructure:
?
?
1. Hardware:
- Generic 50mm/180mm Guidescope, i ordered this one:
it's very light and stiff, comes with mounting options so i even could use one of the threads for the Telrad base to mount it.?
It is almost a crime in imaging to guide with 180mm focal length on 2725mm FL that i am using, but it is enough to provide corrections for and verify guiding down to 0.8" arc seconds total RMS.
?
- 5 meter ST4 cable, if you can find the right length RJ12 6P6C in a local store it will be much cheaper, at least here 3 meters was in stock.
- ZWO ASI 120 MM Mini Guidecamera (comes with a 2 meter ST4 and USB cable). Touptek or a similar brand could have a cheaper alternative.
?
The above hardware was selected because it was the lowest cost alternative that i could find which did not require any modification to my telescope.
?
1. Software?
- PHD2
?
After mounting the Guidescope, connecting the ST4 cable from the Guidecamera to the back of the ServoCAT AUX/AG port and connecting the USB cable from the Guidecamera to your PC you are ready to go from a hardware standpoint except aligning the guidescope with the main scope.
?
In ServoCAT sky i use 6 arc seconds per second for the GUIDE 2 value (0.40 x Sidereal).
?
Download PHD2 and the camera driver, start PHD2 and follow the instructions. When choosing mount select "On camera" and for the Mount guide speed enter 0.30 x Sidereal since the measured guidespeed at least in my case has been lower.
?
The instructions will end with creating a dark library where it asks you to cover the scope, after that the setup is done!
?
Click on the brain icon and choose Algorithms at the top of the window. Change the declination Algorithm to "Hysteresis" like is already selected on RA and make sure dec mode is on auto. In our case RA is AZ and DEC is ALT. Now click on Global and uncheck "use multiple stars" and uncheck Star mass detection.
?
I then pointed the main scope at the moon with a 28mm eyepiece and the guidecamera looping exposures connected to SharpCap. I then adjusted the Guidescope untill the moon was centered in the guidescope as well. You could align the guidescope off center with regards to the main scope as long as the main scope is pointing within the guidescope field of view, and as long as the guidestar you choose when imaging is as close to that point as possible since the field will appear to rotate around the guidestar. PHD2 has a crosshair overlay that can be used.
?
You can now focus the guidecamera on the moon by slightly moving it in or out before locking the lock screws. Personally i reached better focus later on by doing the same on stars (the guide assistant will tell you if you need to focus), be aware that the movements required to reach focus are very small.
?
Make sure that the "Guide" button on the ServoCAT handpad is selected or PHD2 will not be able to send pulse commands.
?
Slew the scope to the South slightly east of the meridian about 35 degrees above the horizon, PHD2 recommends that the calibration should be done close to the Celestial Equator. Begin looping 1s exposures, now slew the scope UP in Alt untill it moves to resolve backlash. Make Sure you are on the east side of the Meridian since Alt will change directions and move down after the meridian.
?
At the bottom of the window hit Guide, now the calibration will start. PHD2 will move the mount East, Weast, North, and South in order to understand how the mount behaves. When the calibration is done click on tools at the top of the window then "review" calibration data.? Verify that between 8-12 steps where used on either axis during the calibration.
?
If much more than 12 steps where used the guidespeed entered when creating the PHD2 profile is faster than the actual guidespeed, that will result in PHD2 not moving the mount enough, the reason being PHD2 sending short guide pulses assuming a fast guidespeed.
?
If less than 8 steps where used that means the entered guidespeed when creating the PHD2 profile is slower than the actual guidespeed, causing PHD2 to send long guidepulses moving the mount to much = same distance covered but with fewer steps.
?
If the guidespeed is incorrect PHD2 advises not to change that manually, but to create a new profile. In the new profile enter the measured guidespeed you got from the calibration.
?
The scope will already have begun guiding after the calibration, and don't worry if the guiding is bad, since the scope is only 35 degrees above the horizon the atmosphere will cause the guidestar to bounce around causing the scope to chase the seeing if it is bad with the 1s exposures from the calibration.
?
Stop guiding and slew to the object, loop 2s exposures and begin guiding and wait a minute or so, then click tools on the top of the window then choose "Guiding assistant". PHD2 will stop guiding and measure the mounts unguided tracking performance/behaviour. Uncheck "Measure declination backlash" in the lower left corner.
?
PHD2 recommends waiting 2 minutes, click on "STOP" and follow the recommendations, you don't have to go and change the settings, you simply press on "apply" for the suggestions PHD2 comes up with, with the exception of improving guidescope focus which it may suggest, or polar alignment which is not relevant for us.
?
If you after all this see very large guidestar deflections especially after corrections, the PHD2 documentation recommends that you should not wildly begin changing settings, you should however take a closer look at how the guidescope is mounted.
?
Just a few microns of flexure is capable of throwing of the guidestar by 6 arc seconds, several star diameters, a human hair is 50 microns thick.
?
I followed that recommendation and tightened the adjustments screws as best i could on the Guidescope, it did change the pointing of the guidescope slighlty but my main scope is still pointing in the lower right corner of the Guidescope field of view so i just select guidestars there instead. It helped a lot taming the deflections.
?
Besides that seeing plays a huge roll, if the seeing is really bad guiding will be bad since the stars will move even if the scope is not moving.
?
If the seeing is good, guiding should work very well, If the guiding looks bad but the exposures look good, don't worry about the guidegraph, if the guidegraph looks bad and the exposures are bad then it's worth taking a look at.
?
I tested this 2 days ago for 1 hour on M106 and it stayed locked with M106 exactly in the center for 1 hour with 1-1.3 arc seconds total RMS guiding with round stars.
?
I did not mention the following above to not complicate things but it is possible to connect the Meade Generic or ServoCAT? driver to PHD2 in order to provide PHD2 with pointing information so that it can use dec compensation. If you use "On Camera" like i have suggested above you will have to enter the DEC (ALT) manually before calibration and before guiding on a new object.
?
?
Clear skies!
Gabriel
?
?
?
?
?
?
?
?
 
Edited

Thank you Gary, happy to help!
?
Great tip, this also means you will visually get a rough idea/understanding of the guide calibration, so when PHD2 moves the scope east, back west, north back to south the path in a perfect calibration should create a 90¡ã degree angle. (also visualized in review calibration data).
?
In other words in such a scenario the scope is fully responsive to PHD2 pulse commands, if the angles are questionable it could be because of backlash or poor unguided tracking.
?
With a good 2-star alignment i get a very good calibration, yesterday with EasyTrack i got the warning: "RA and DEC angles are questionable guiding may be impaired" but as you can see guiding can still work well despite a warning.
?
If tracking is slightly off prior to performing the calibration, click on the brain icon and then on guiding? at the top of the window if I remember correctly, then check "assume RA/AZ orthogonal to DEC/ALT" so that the RA/AZ tracking error does not affect the DEC/ALT calibration.
?
/Gabriel?
?
?
 

Update:
?
I got sub arc second guiding with Easytrack and Autoguide when i was out a few days ago: (Graph uploaded on Astrobin)
?
?
Even though it is possible to calibrate (with a warning from PHD2 after the result) and also guide at the celestial equator, i get? a much better calibration at for example 60 degrees azimuth and 30-40 degrees in altitude. Probably beacuse the Altitude rate is almost zero at the celestial equator.
?
It's probably best to calibrate at the same azimuth as the object that will be imaged and at 30-40 degrees above the horizon with dec compensation.
?
The key to get a good calibration in PHD2 is to make sure it uses 8-12 steps per axis. With 6 arc seconds per second in ServoCAT Sky for the GUIDE 2 value and a calibration step size of around 5000 ms (pulse) results in 8-12 steps.
?
If the calibration step size is say 2300 ms you simple change the guidespeed x sidereal in the box above when on the guiding tab in PHD2 untill you get a step size of around 5000ms (not necessary to create a new profile). However, if i was to lower or increase the GUIDE 2 value in ServoCAT Sky, 5000ms steps size would no longer result in 8-12 steps. Also not sure if the GUIDE 2 value on a Starstructure would translate to other dobs.
?
Here is how my latest calibration looks like:
?
?
?
/Gabriel
?
?
?
 

Needed !!

Cheers
Wes Smith?


On Tue, Feb 18, 2025 at 4:03?AM Gabriel Wiklund via <gabriel.wiklundholeshot=[email protected]> wrote:

Here comes a description of the hardware and settings i have used to successfully Autoguide with my ServoCat driven Starstructure:
?
?
1. Hardware:
- Generic 50mm/180mm Guidescope, i ordered this one:
it's very light and stiff, comes with mounting options so i even could use one of the threads for the Telrad base to mount it.?
It is almost a crime in imaging to guide with 180mm focal length on 2725mm FL that i am using, but it is enough to provide corrections for and verify guiding down to 0.8" arc seconds total RMS.
?
- 5 meter ST4 cable, if you can find the right length RJ12 6P6C in a local store it will be much cheaper, at least here 3 meters was in stock.
- ZWO ASI 120 MM Mini Guidecamera (comes with a 2 meter ST4 and USB cable). Touptek or a similar brand could have a cheaper alternative.
?
The above hardware was selected because it was the lowest cost alternative that i could find which did not require any modification to my telescope.
?
1. Software?
- PHD2
?
After mounting the Guidescope, connecting the ST4 cable from the Guidecamera to the back of the ServoCAT AUX/AG port and connecting the USB cable from the Guidecamera to your PC you are ready to go from a hardware standpoint except aligning the guidescope with the main scope.
?
In ServoCAT sky i use 6 arc seconds per second for the GUIDE 2 value (0.40 x Sidereal).
?
Download PHD2 and the camera driver, start PHD2 and follow the instructions. When choosing mount select "On camera" and for the Mount guide speed enter 0.30 x Sidereal since the measured guidespeed at least in my case has been lower.
?
The instructions will end with creating a dark library where it asks you to cover the scope, after that the setup is done!
?
Click on the brain icon and choose Algorithms at the top of the window. Change the declination Algorithm to "Hysteresis" like is already selected on RA and make sure dec mode is on auto. In our case RA is AZ and DEC is ALT. Now click on Global and uncheck "use multiple stars" and uncheck Star mass detection.
?
I then pointed the main scope at the moon with a 28mm eyepiece and the guidecamera looping exposures connected to SharpCap. I then adjusted the Guidescope untill the moon was centered in the guidescope as well. You could align the guidescope off center with regards to the main scope as long as the main scope is pointing within the guidescope field of view, and as long as the guidestar you choose when imaging is as close to that point as possible since the field will appear to rotate around the guidestar. PHD2 has a crosshair overlay that can be used.
?
You can now focus the guidecamera on the moon by slightly moving it in or out before locking the lock screws. Personally i reached better focus later on by doing the same on stars (the guide assistant will tell you if you need to focus), be aware that the movements required to reach focus are very small.
?
Make sure that the "Guide" button on the ServoCAT handpad is selected or PHD2 will not be able to send pulse commands.
?
Slew the scope to the South about 35 degrees above the horizon, PHD2 recommends that the calibration should be done close to the Celestial Equator. Begin looping 1s exposures, now slew the scope UP in Alt untill it moves to resolve backlash.
?
At the bottom of the window hit Guide, now the calibration will start. PHD2 will move the mount East, Weast, North, and South in order to understand how the mount behaves. When the calibration is done click on tools at the top of the window then "review" calibration data.? Verify that between 8-12 steps where used on either axis during the calibration.
?
If much more than 12 steps where used the guidespeed entered when creating the PHD2 profile is faster than the actual guidespeed, that will result in PHD2 not moving the mount enough, the reason being PHD2 sending short guide pulses assuming a fast guidespeed.
?
If less than 8 steps where used that means the entered guidespeed when creating the PHD2 profile is slower than the actual guidespeed, causing PHD2 to send long guidepulses moving the mount to much = same distance covered but with fewer steps.
?
If the guidespeed is incorrect PHD2 advises not to change that manually, but to create a new profile. In the new profile enter the measured guidespeed you got from the calibration.
?
The scope will already have begun guiding after the calibration, and don't worry if the guiding is bad, since the scope is only 35 degrees above the horizon the atmosphere will cause the guidestar to bounce around causing the scope to chase the seeing if it is bad with the 1s exposures from the calibration.
?
Stop guiding and slew to the object, loop 2s exposures and begin guiding and wait a minute or so, then click tools on the top of the window then choose "Guiding assistant". PHD2 will stop guiding and measure the mounts unguided tracking performance/behaviour. Uncheck "Measure declination backlash" in the lower left corner.
?
PHD2 recommends waiting 2 minutes, click on "STOP" and follow the recommendations, you don't have to go and change the settings, you simply press on "apply" for the suggestions PHD2 comes up with, with the exception of improving guidescope focus which it may suggest, or polar alignment which is not relevant for us.
?
If you after all this see very large guidestar deflections especially after corrections, the PHD2 documentation recommends that you should not wildly begin changing settings, you should however take a closer look at how the guidescope is mounted.
?
Just a few microns of flexure is capable of throwing of the guidestar by 6 arc seconds, several star diameters, a human hair is 50 microns thick.
?
I followed that recommendation and tightened the adjustments screws as best i could on the Guidescope, it did change the pointing of the guidescope slighlty but my main scope is still pointing in the lower right corner of the Guidescope field of view so i just select guidestars there instead. It helped a lot taming the deflections.
?
Besides that seeing plays a huge roll, if the seeing is really bad guiding will be bad since the stars will move even if the scope is not moving.
?
If the seeing is good, guiding should work very well, If the guiding looks bad but the exposures look good, don't worry about the guidegraph, if the guidegraph looks bad and the exposures are bad then it's worth taking a look at.
?
I tested this 2 days ago for 1 hour on M106 and it stayed locked with M106 exactly in the center for 1 hour with 1-1.3 arc seconds total RMS guiding with round stars.
?
I did not mention the following above to not complicate things but it is possible to connect the Meade Generic or ServoCAT? driver to PHD2 in order to provide PHD2 with pointing information so that it can use dec compensation. If you use "On Camera" like i have suggested above you will have to enter the DEC (ALT) manually before calibration and before guiding on a new object.
?
?
Clear skies!
Gabriel
?
?
?
?
?
?
?
?
 

Waouh !!
Just amazing what accuracy you get from just a 180 mm focal length guiding your 2700 mm focal length scope !!!!
and in easy track mode !!!
A friend of mine was saying to me yesterday that auto guiding is normally done with a FL of 1/4 of the main scope FL that would be 2700/4=675 mm FL !
Congratulations !!
You indicate
??With 6 arc seconds per second in ServoCAT Sky for the GUIDE 2 value and a calibration step size of around 5000 ms (pulse) results in 8-12 steps ?
What is a ? step ? ?
and how do you calculate 8-12 steps ?
I¡¯m ?also surprised by the 5000 ms pulse?
you mean PHD2 is sending a correction a track rate for 5 seconds ?! I thought it was only correcting with small pulses like <500 ms¡­
thanks for reply
Raphael
?
 
Edited

Yes i was surprised too,
?
Thank you!
?
The calibration in PHD2 is automatic, so you just press and wait. PHD2 calculates the pulse to be sent for each calibration step from the values you have entered in the Profile, such as FL of the guidescope and guidespeed.
?
If the values are correct, the automatic PHD2 calibration will take 8-12 steps to complete in AZ and 8-12 steps to complete in ALT.?
?
However If it takes 50 steps or 5 steps then something entered when creating the profile like the guidespeed is incorrect.
?
When PHD2 is performing the calibration it is moving the mount pretty fast West then East, North then South (in order to understand how the mount is behaving), that's why the pulse is 5000ms with a slow guidespeed.
?
During guiding the pulses will be very small, yes below 500 ms, (even though i have a very slow guidespeed).
?
Best Regards
Gabriel
?
?
 

Gabriel,?

So - you are not setting "5000" anywhere?
It is a result of or what is used by the program when doing autocalibrate??

I ask because I don't remember anywhere to set the pulse duration.?

Gary




------ Original Message ------
From "Gabriel Wiklund via groups.io" <gabriel.wiklundholeshot@...>
Date 2/22/2025 7:02:36 AM
Subject Re: [ServoCAT] Settings for use of AutoGUIDE

[Edited Message Follows]

Yes i was surprised too,
?
Thank you!
?
The calibration in PHD2 is automatic, so you just press and wait. PHD2 calculates the pulse to be sent for each calibration step from the values you have entered in the Profile, such as FL of the guidescope and guidespeed.
?
If the values are correct, the automatic PHD2 calibration will take 8-12 steps to complete in AZ and 8-12 steps to complete in ALT.?
?
However If it takes 50 steps or 5 steps then something entered when creating the profile like the guidespeed is incorrect.
?
When PHD2 is performing the calibration it is moving the mount pretty fast West then East, North then South (in order to understand how the mount is behaving), that's why the pulse is 5000ms with a slow guidespeed.
?
During guiding the pulses will be very small, yes below 500 ms, (even though i have a very slow guidespeed).
?
Best Regards
Gabriel
?
?
 
Edited

Hello Gary,
?
That is correct.
?
However, when guiding at the bottom to the right you can set MAX pulse duration in AZ and ALT, default is 2500 ms which i have not found a reason to change.
?
Even if you would change the calibration step size on brain -> guiding ->calibration step (ms): next to Advanced it will automatically change back to the value calculated by the values entered when creating the profile and also depending on guidspeed entered which is found when clicking on Advanced.
?
You have to keep an eye on what the number is on calibration step (ms): since it could suddenly change for example if there is a different guidespeed in the Meade Generic driver if connected so the guidespeed there could overwrite the guidespeed in PHD2.
?
It once changed to 2300ms for me and i am not sure why. PHD2 recommends that you should create a new profile if a parameter has changed and not do manual changes, pherhaps that is the reason.
?
However i have found that, as long as you keep an eye on that number and it works i have not found a reason to create a profile from scratch.
?
Best regards
Gabriel
 
Edited

I made some new discoveries this morning when creating a new profile to improve my understanding of PHD2.
?
1. It is not possible, when creating a new profile to enter a mount speed less then 0.20 x Sidereal. It's only possible when changing the settings later. (that would be 3.01 arc seconds per second in the Meade Generic driver (if used) before creating a new profile in PHD2 change that in the driver)
?
2. The calibration step size is not only calculated from guidespeed, focal length, and pixel size but also which declination the calibration will be performed, this can be set under Advanced settings.
?
This explains why the calibration step size suddenly changed for me, i was calibrating at a different declination and PHD2 used the pointing information from the Meade driver to use "dec compensation".
?
Since the PHD2 documentation advises against changing guidespeed after creating a new profile, it's probably best to go with 0.20 x Sidereal from the start and leave it.
?
The last calibration that i did, which was Orthogonal, completed in both axis within 8-12 steps and produced good guiding results was done at about 60 AZ and 38 ALT and declination of 46.
?
I had changed guidespeed to 0.18 x Sidereal in PHD2 and as usual 6 arc seconds per second in Servocat Sky, Calibration step size was 4900 ms.
With the new profile i set all the values the same, including declination 46 for the calibration, produced a step size of 4300 ms, since guidespeed had been raised from 0.18 to 0.20 Sidereal.
?
Since the step size is reduced, in order to not slow down the measured guidespeed with 0.20 x Sidereal set in PHD2 it's probably a good idea to use 7 arc seconds per second in ServoCAT sky instead of 6 arc seconds per second, i have changed this in ServoCAT sky.
?
Will be interesting to see next clear night when i will be using the DSC Pro and hopefully do actual capture.
?
?
Here is an extreme crop (to see the stars better) of 180 stacked subs, 20 seconds each processed in Siril on a random part of the sky near Ursa Major, it is from the night when i got around 0.95" RMS guiding with EasyTrack.
?
The stack had a FWHM of 3.4 arc seconds, which is what i get when looping 1 second exposures on a night when seeing is above average from this location.
?
?
Edit (correction): The measured guidespeed will not slow down because of increasing the guidespeed from 0.18 to 0.20 in PHD2, but it will send shorter pulse commands and that will increase the number of steps used during calibration, and to compensate for that it would not hurt to increase the guidespeed in ServoCAT Sky if the number of steps are more than 12.
?
/Gabriel
 

Thanks Gabriel
Even if don¡¯t understand everything detail you explain, all this will be of great use for community including me when I have a higher level in astrophotography
One question :?
With the very good result you have with auto guiding + easy track, do you see any advantage to make auto guiding with 2 alignment star versus auto guiding+ easy track ?
Pointing is more accurate with 2 stars alignment, but appart from this, any advantage of 1 method versus the other ?
thanks
Rapha?l?
?
 
Edited

Your welcome Raphael, thank you. Happy to help!
?
I don't see any advantage of imaging with autoguiding in combination with easytrack except if your DSC is not working, so a good backup solution!
PHD2 will not have to work/correct as much when you have done the 2-star alignment because of more accurate tracking, but it could potentially still correct to the same RMS error.
?
PHD2 is very good, and made for correcting low frequency errors like slow drift. Which is the case when using easytrack compared to a good 2-star alignment.
?
Edit: It is not possible to point at all with Easytrack, you would have to use a Telrad or similar, just like when doing visual.
?
/Gabriel
?
 
Edited

Update:
?
I have come to the conclusion that 7 arc seconds per second in ServoCAT sky is not fast enough to calibrate or guide well between 160 Az? and 200 az (so +/- 20 degrees of south), same to the north 330 - 30 az. So in other words, stay away from the Meridian and 20 degrees on either side of it.
?
At 75 z and 37 Alt i get a perfect calibration in PHD2 with 7 arc seconds / second set in ServoCAT Sky.
?
Due to field rotation one would want to stay away from the meridian anyway, also considering objects are the highest above the horizon when passing the meridian.
?
This is not really an issue if one plans the session: To give an example:
?
If i was to image M106 tonight, and i would begin imaging at around 8 PM when it is at 67 az and 42 alt, i will still get 5 hours of imaging time before it reaches 160 az and 75 alt.
?
I don't think it's worth changing the guidespeed for imaging around the meridian since, the span is a short, as mentioned field rotation and at least from my experience a fast guidespeed does not work well, at least with my Starstructure.
?
/Gabriel?
 

Gabriel,
I am still trying to understand all of this. One big question I have is: does calibration need to be done for every object or every session?
Also I think an issue for me is going to be a limitation in objects with a decent enough imaging length because my horizon up to about 40 degrees is obstructed all around me due to trees.
?
I think if I try this with my dob (A 18¡± f4.3 Astrosystems) mechanically, at least might work well since I have combination Teflon and roller bearings mitigating any stiction in az or alt. I do have a lot of backlash in both axes that I need to counteract using Gary¡¯s excellent procedure.

For possible guidescopes I currently only have 2 options 1) An 80mm Lumicon Superfinder. Not sure of its fl but I believe it is very short so may not work. Other option is a Primaluce Lab 60mm guide scope that is 240mm fl. Which might work

?
Mike
 
Edited

Hi Mike,
?
No, when using the ST4 cable and checking "use dec compensation" in PHD2 settings you only have to calibrate once in the beginning of the evening. At the moment i calibrate at about 90 AZ and 38 ALT, works well.
?
If you don't connect to the mount in PHD2 you will be promted to enter the dec (alt) before calibration and before starting to guide, if you connect to a mount driver PHD2 will automatically know where the scope is pointing in the sky.
?
if you check "Auto-restore calibration" in PHD2 settings you will not have to calibrate upon each new session either.
?
However my take is, that since the scope due to say humidity or some other factor may move mor easily one night than another pherhaps it's best to calibrate before each session so that PHD2 understands how the scope behaves that night, and you will also see that if the measured guidespeed is a lot less than the previous session pherhaps the bearings are not clean ore something like that which you could adress before imaging.
?
But my guess is you could probably get away with calibrating once then just imaging night after night.
?
Actually i avoid objects below 40 degrees so i often begin right around there so it has not been an issue getting 2-3 hours on an object provided i do som planing in Stellarium.
?
To be really effective and minimize the effects of field rotation you can do 30-60 minutes on several objects during a night and continue adding time on them several nights at the same position they where the previous nights, so after many nights you would have many objects with much time where the frames will not have been rotated that much compared to tracking a single object one night for 3 hours.
?
I also had massive backlash and did Gary's procedure however backlash comp does not work with autoguiding for some reason, the stars look like the scope has been hit by a wind gust, it's even written in PHD2 documentation to not use any backlash compensation outside the software.
?
So i set the backlash comp to 0 in both alt and az in ServoCAT Sky and thought it would be a disaster, but no problem at all. As long as you slew UP untill the scope moves before doing PHD2 calibration no problem, and when autoguiding it has not been a problem at all either, pherhaps the motors never change directions only speed.
?
I am a bit confused, because in PHD2 my scope shows less backlash than the dedicated AP rig i had (when changing from north step to south step). With the Virtual handpad in NINA backlash is more evident and with the physical handpad my backlash in alt is massive.
?
?
My guidescope only has a focal length of only 180mm so no problem!?
?
/Gabriel
?
?

1 - 20 of 25