Transcript Astrophotography

Autoguiding
Deep Dive Into
Contents
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Introduction
Brief on Basic’s Guide
Technical Blurb
PHD Guiding Software
PHD Advanced Settings
EQMod Pulse Guiding
Conclusion/Tips/Closing
Introduction
Thank you for the opportunity to speak to you all today, my name is Anthony Grimshaw and
I am an Astrophotography Amateur and have been in the hobby for about 18 months now.
I work in IT and have done for about 12 years, prior to this I was in the NAVY as a marine
technician. I have found the combination of my professions have helped me greatly in the
endeavours of my hobby.
Let me start by stating I am no expert on Astrophotography and everything I have learnt to
date has been through my time in the field, speaking with others and reading information
from books and the Internet.
During this time I have found that Autoguiding tends to be a sticking point for many
(including myself), so today I am hoping to share my experiences with Auto guiding
(specifically PHD), how it works and the settings you have available to make it work best for
your specific set up.
Introduction Con’t
This presentation is not a silver bullet session to fix all your problems, however I do hope
the following information will assist in getting guiding working for you and ultimately
getting you good images.
I apologise in advance; these are complex tool sets with numerous settings and interfaces.
In order to cover this adequately it will be
Death by Power Point
Brief on Basics
In my presentation earlier in the week I did a discussion on Auto Guiding basics, this
covered basic concepts about the how’s and what’s of guiding. In a nut shell from that
discussion:
Auto guiding is the use of an electronic tool or system to assist your telescope mount
from drifting or moving off the intended imaging target during long exposures.
Auto guiding does this by tracking a star in the same or close proximity to that of your
imaging target and sending adjustment commands to your mounts control system to
correct for any apparent movement.
Guiding is required because even the best mounts cannot achieve the level of
accuracy required to track celestial bodies without error (especially at longer focal
lengths).
Brief on Basics Con’t
This is due to:
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the drive gears
in other areas of machining of the mount
play in the ball bearings that permits their rotation
Movement or Flexing in mount and brackets
Misalignment from the celestial pole
What Auto Guiding can do
for your images.
Technical Blurb
Most Modern telescope mounts use a control system called an “open loop” controller
(also called a non-feedback controller) this is a type of controller that computes its
input into a system using only the current state and its model of the system. A
characteristic of the open-loop controller is that it does not use feedback to determine
if its output has achieved the desired goal of the input.
This means that the system does not observe the
output of the processes that it is controlling.
Consequently, an open loop system cannot correct any
errors that it could make and it cannot compensate for
disturbances in the system.
Open loop controllers are chosen as they are simpler to
manufacture and therefore much cheaper to make and
subsequently cheaper to purchase.
Technical Blurb con’t
To avoid the problems of open-loop controllers, a feedback circuit can be introduced.
The feedback circuit effectively closes the loop and creates a closed-loop controller.
Closed loop controllers have the following advantages over open loop controllers:
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disturbance rejection (such as unmeasured friction in a motor).
guaranteed performance even with model uncertainties, when the model structure does not
match perfectly the real process and the model parameters are not exact (e.g. poor polar
alignment)
unstable processes can be stabilized
reduced sensitivity to parameter variations
improved reference tracking performance
Autoguiding is for all intents and purposes a system that provides the components
required to create a closed loop system and provides the above benefits.
PHD Guiding Software
There are a range of products and tools available for Auto Guiding, however today I am
going to discuss the details of PHD Guiding, primarily because it is free, however it’s also a
very powerful tool that will meet the requirements of most amateur Astro-Photographer’s.
PHD “Press Here Dummy” was written by Craig Stark of Stark Labs, Craig has a PH.D in his
own right; however he found it difficult to manually guide his scope so he wrote PHD as his
answer to the problem. It can be found at http://www.stark-labs.com/index.html. I have a
copy if anyone requires it?
PHD literally stand for:
Press
Here
Dummy
So it’s supposed to be
easy to use.
PHD Guiding Software Con’t
When you open PHD you are presented
with the following screen
• It comprises the menu bar at the top:
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Of interest is the Mount drop down
and
The Tools Menu
• The command buttons at the bottom:
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Of interest is the Camera selection
button
Telescope connection button
Loop exposure button
PHD Target button (Start PHD Guiding)
Stop button to stop PHD
Exposure Time and
The Brains Button
PHD Guiding Software Con’t
The mount selection list allows you to
chose your mount type.
The three main ones in common use are:
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ASCOM
GPUSB
On-Camera
(Connects into EQMod or ASCOM)
(Connects to GPUSB Box)
(Uses on board camera control)
All the settings discussed in part one cover
PHD and all of the above connection
types.
Part two will cover the connection to
EQMod and how you can fine tune PHD’s
outputs further.
PHD Guiding Software Con’t
The tools selection list allows you to
choose to enable some options and
features.
The two options you should enable are:
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Enable Logging
Enable Server
Optionally enable the Bullseye or Grid to
help track stars movements, or to assist in
pointing error adjustments/drift aligning.
Optionally enable the Graph to see the
Guiding outputs.
PHD Guiding Software Con’t
If you want a quick start guide have a look
under the help menu for the “Impatient
Instructions”.
This does not cover any specifics but is the
basics to get PHD running.
PHD Guiding Software Con’t
Most importantly the PHD Brains Button,
this sets the advanced values for how PHD
talks to your mount/software, It has the
following values:
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RA Aggressiveness
RA Hysteresis
Max RA Duration (ms)
Search Region (pixels)
Min. motion (pixels)
Calibration Step (ms)
Time Lapse (ms)
LE Port
Force Calibration
Log info
Disable guide output
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Dec guide mode
Dec Algorithm
Dec slope weight
Max Dec duration (ms)
Star mass tolerance
Noise Reduction
Camera gain %
LE Read Delay
Dither scale
RA-only dither
Use subframes
Defaults are displayed
PHD Advanced Settings
So what do these settings do and what do they mean?
RA Aggressiveness –
The RA Aggressiveness setting is used to adjust the % of correction PHD makes to the
mount, for example when set at 120 PHD will apply 120% of the correction to the RA
drive to that detected by PHD and the stars movement. Usually a setting from 80 to
100 would be suffice, I would not recommend anything over 100.
Default
Recommended
= 100
= 100 or less if oscillating occurs.
PHD Advanced Settings Con’t
RA hysteresis –
Hysteresis (% Value) is the dependence of a system not only on its current
environmental state but also on its past environment, meaning PHD can evaluate its
past corrections and compensate for these corrections in the future.
The idea here is that a quick change in the measured error in guide star position is
probably due to a bad measurement (perhaps due to atmospheric disturbance), so the
correction is "diluted" by mixing in some of the recent correction trends. In addition to
sensitivity to seeing conditions, this setting is influenced by the characteristics of the
mount.
A good mount will not have sudden large changes in the RA position, so a large
hysteresis setting is appropriate to filter out bad measurements.
PHD Advanced Settings Con’t
RA hysteresis con’t –
If your mount has a high rate of reproducible error, a number such as 30 – 45 is
probably okay, but for a lower quality mount a value of 10 is likely a better as sudden
large errors can occur and you want PHD to react to these.
Default
Recommended
= 10 %
= Start at 10 and increase if your mount allows.
PHD Advanced Settings Con’t
Max RA Duration (ms) –
The Max RA Duration setting determines how large the maximum correction PHD is
allowed to make (in milliseconds).
The idea here is to limit the damage caused by bad measurements of the guide star
position. Allowing a very large correction (in one cycle) might require a large
correction in the other direction later. If there really is a large error the exposure is
probably ruined anyway, but in any case it isn't going to be much worse by breaking up
the correction into multiple cycles, which is what happens when the max duration
limit is hit.
Unlike parameters specified in pixels, the proper setting for such timing parameters
depends on the guide rate set in the mount. With the typical guide rate of 0.5X (50%),
the max RA duration should be set at something like 300 milliseconds.
PHD Advanced Settings Con’t
Max RA Duration (ms) con’t –
Another consideration is that in most mounts (especially using an ST-4 guide port) the
guiding process is delayed for the duration of the correction pulse, so allowing a large
correction in one axis may delay a necessary correction in the other.
***NOTE*** Theoretically, guiding through a serial link to the mount (usually via an
ASCOM driver) could make the correction more quickly, but this is generally not done.
The next guide exposure cannot begin until the mount movement is done.
Default
Recommended
= 1000
= Start at around 300 and slowly work up if constantly reaching
this limit, if however you hit the limit constantly you probably
have other issues guiding cannot compensate for such as poor
alignment.
PHD Advanced Settings Con’t
Search Region (pixels) –
Search Region (pixels) defines the size of the area to search for the star to find its new
position (the little green square around your selected guide star).
The default of 15 pixels (i.e., a 30 x 30 area) is generally adequate. Larger areas take
more time to process and if the guide star moves that far off you've got a serious
problem that guiding is probably not going to fix anyway.
Default
Recommended
= 15
= 15
PHD Advanced Settings Con’t
Min Motion (pixels) –
The Min Motion setting is the value that sets the minimum amount the guide star is
allowed to move “without” triggering a correction, this setting applies to both the RA
and DEC axis guide commands.
If the value was set to 0.25 as an example the guide star would be allowed to “move
around" a quarter pixel without PHD sending corrections commands.
A setting of 0.05 means if PHD sees movement of a 20th of a pixel movement it will
send a correction command and this is likely far to aggressive.
PHD Advanced Settings Con’t
Min Motion (pixels) con’t –
The default setting of 0.15 is typically suitable for most mounts, however it will
depend to some degree on the relative magnification of the guide system / imaging
system as well as on the seeing conditions and the quality of the mount.
Default
Recommended
= 0.15
= 0.15 Can be more relaxed if the guide scope is of higher
magnification when compared to the imaging scope.
PHD Advanced Settings Con’t
Calibration Step (ms) –
The Calibration step value is the length of a pulse in milliseconds that PHD will send to
your mount during the calibration process.
There is no easy recommendation for this parameter that will fit all telescope mounts
and image set ups as it depends heavily on what the guide scope magnification is and
what the guide rate is set in the mount. If you wish to adjust do the following:
During calibration, look at the status bar to see how much the selected star has moved
from the initial position. If the guide star is moving just a few pixels per iteration you
could speed things up by using a larger setting for calibration step.
PHD Advanced Settings Con’t
Calibration Step (ms) con’t –
On the other hand, if it exceeds the goal in just a couple of calibration steps the
calibration may not be as accurate. ***NOTE*** a high degree of accuracy in
calibration is not always necessary. If it takes at least 4 iterations it's probably close
enough.
***Note*** that this setting also defines the duration of pulses used to manually
guide the mount. After calibration is done you can safely change this setting to the
duration you want for manual guiding, but remember to change it back before you
calibrate again.
Default
Recommended
= 750
= Start with the default setting of 750ms and adjust only if you
have issues getting a calibration to work properly.
PHD Advanced Settings Con’t
Time Lapse (ms) –
Despite the name indicating some sort of time lapse recording, the Time lapse setting
provides a delay after each guide command before the next guide camera exposure
starts.
This is used because in some cases the mounts movement may not be complete or
may not have settled when the correction is complete. Setting some delay here will
provide time for the mount to settle so that the next exposure is done entirely at the
new position.
Default
Recommended
=0
= 0 (Only change if you have a lot of oscillation in your guiding and
only after you have trimmed the Aggressiveness settings down.
PHD Advanced Settings Con’t
Dec Guide Mode –
The DEC guide mode has 4 settings “Off/Auto/North/south”. This setting essentially
disables or restricts how PHD can send Declination adjustments to the mount.
Normally you would leave this set at "Auto" however if your polar alignment is
excellent you might prefer to set it to “Off” to avoid spurious DEC corrections.
Likewise if your DEC was drifting in one direction you can note which way it's drifting
and enable corrections only in the direction required to compensate. This can be
advantageous because it avoids sending DEC corrections that aren't really necessary.
Default
Recommended
= Auto
= Auto
PHD Advanced Settings Con’t
Dec Algorithm –
The DEC Algorithm setting has two available values “Lowpass filter/Resist switch”,
Resist switch means that PHD will make corrections normally if they are in the same
direction as recent corrections, but will ignore small errors in the other direction until
they become large.
The lowpass filter option effectively averages the corrections so that most spurious
movements are avoided, but small steps to correct for drift are applied. If DEC guide
mode is set to "North" or "South" a setting of "Resist switching" has no effect, so
lowpass filtering would be the better choice.
***NOTE*** The Lowpass Filter setting is reported not to work correctly in the current
versions of PHD, I cannot verify this however.
Default = resist switch
PHD Advanced Settings Con’t
Dec Slope Weight –
The DEC slope weight setting does not have a lot of information available for it,
however as I understand it the Dec slope weight changes the damping of the low pass
filter and only comes into effect if you've selected "low pass filter" for the Dec mode.
Again I cannot verify this setting so I suggest using the default value of 5.
Default
Recommended
=5
=5
PHD Advanced Settings Con’t
Max Dec Duration (ms) –
Max Dec Duration setting determines how large of the maximum correction PHD is
allowed to make to the Declination axis (in milliseconds) in one adjustment.
150 is probably adequate unless things are considerably bad, such as massive periodic
error or poor polar alignment. You can raise it to, say, 800, but If PHD needs to send an
800ms pulse then you've most likely got serious polar alignment problems that you're
asking to guider to accommodate for that are probably unreasonable.
I'd recommend rather than increasing that number too high (300 should be the
maximum for almost any mount), learn how to better polar align or fix the problems
with the mount that are causing large movements rather than adjust this value too far.
Default
= 150
Recommended
= 150 (Max 300 if reaching this limit frequently)
PHD Advanced Settings Con’t
Star Mass Tolerance –
The Star Mass Tolerance setting is designed to ensure that it is guiding on the correct
star, PHD checks the "star mass" (how bright it is) on each exposure.
If the stars brightness changes by a factor greater than the specified tolerance, a
warning will sound. A value of 0.5 is reasonable, but you may sometimes get false
warnings due to various conditions that affect the apparent brightness. In this case,
you can avoid the warnings by setting a higher tolerance. A setting of 1.0 disables the
feature.
Default
Recommended
= 0.5
= 0.5
PHD Advanced Settings Con’t
Noise Reduction –
The Noise reduction setting has 3 available options (none/2x2/3x3), this is normally
set to "none" however if you're working with a dim guide star and can't increase the
exposure time, you might want to try one of the other settings.
What it does is trade off resolution for sensitivity (like binning, but done after the
capture rather than in the camera). This can be especially useful for cameras that have
very small pixels. Such cameras may provide more resolution than is useful, but suffer
from low sensitivity and noise that degrades the accuracy with which PHD can
calculate the centroid of the guide star.
Default
Recommended
= None
= None (however play with this if you are having difficulty finding
guide stars and maintaining them.
PHD Advanced Settings Con’t
Camera Gain % –
The Camera Gain setting is only available with some types of cameras and the
recommended setting depends on the camera model. In general, you want to use the
setting that provides the best signal to noise ratio for your guide star.
This setting multiplies the amount of output signal from the camera per photon
registered.
Default
Recommended
= 95%
= 95% But depends on the camera and it’s sensitivity.
PHD Advanced Settings Con’t
LE Port and LE Read Delay –
The LE port and LE read delay settings apply only to guide cameras that use parallel or
serial ports on the computer to control the "long exposure" mode of a modified
webcam; I have not used or modified these settings in any way so I cannot comment
on the effect on the guiding system.
Default = Port 378
Default = 0 delay
Is there anyone here who has experience in this area that would like to comment?
PHD Advanced Settings Con’t
Force Calibration –
The Force calibration check box is used to force PHD to rerun a calibration cycle before
it starts guiding. When unchecked, PHD will use the previous calibration data and
begin guiding immediately when the target icon is clicked.
PHD automatically “checks” this item when first launched and “unchecks” it when a
calibration is successfully completed.
It is recommended to check this if you move to a different part of the sky to force a
new calibration cycle.
PHD Advanced Settings Con’t
Log Info –
The Log info check box when checked will write all PHD calibration and guiding
information into a log file. I recommend leaving this checked so that you can later
check how well the guiding performed. Not that you may do any checks, it’s still good
to know that you can investigate any problems later if necessary. The log files are very
small so do not worry about leaving logging running.
***NOTE*** PHD creates a new file for each date in which logging is started. This is
much better than simply overwriting the old file (which older versions did), but it can
still be confusing if you start logging after midnight on one night and then start it again
before midnight the next night.
PHD Advanced Settings Con’t
Log Info Con’t –
The default location for the log files are the “My Documents” folder on windows PC’s
and they are saved in the following format: PHD_log_DDMMMYY.log
Default
Recommended
= Unchecked
= Checked
PHD Advanced Settings Con’t
Disable Guide Output –
The Disable guide output check box when checked tells PHD to do everything the
same with the exception of sending the correction commands to the mount. This is
useful because it allows you to study the behaviour of the mount without guiding.
In particular, by disabling the output and enabling logging you can create a log file that
can be imported into a program to analyse the mount's periodic error and generate a
periodic error correction (PEC) file.
Default
Recommended
= Unchecked
= When guiding! Naturally unchecked 
PHD Advanced Settings Con’t
RA-Only Dither –
The RA-only dither check box tells PHD to only send dithering commands to the RA
axis only not DEC, under normal conditions dithering is applied to both RA and DEC.
Dither changes only in RA is a good idea if you have problems guiding in DEC because
it might take too long for DEC to settle after a dither move.
For those that don’t know dithering is a command that can be sent to PHD to move
the guide star X and Y distance from its current position and is used to help remove
noise from your image stacks.
***NOTE*** The Enable Server Option must be enabled for software to send these
commands to PHD.
Default
Recommended
= Unchecked
= Unchecked
PHD Advanced Settings Con’t
Use Sub Frames –
The Use subframes check box allows Cameras that support this feature to read out
from pixels from only a portion of the image captured.
If selected and your camera supports the feature, PHD will use it to decrease the
amount of time it takes to download an image by reading only the area around the
guide star (the search region).
Default
Recommended
= Unchecked
= Unchecked (unless supported by your camera).
PHD Advanced Settings Con’t
PHD Advanced Settings Conclusion –
PHD has a number of options available to you to assist in your guiding, while PHD is
generally quite good when set at the defaults, however it is set this way to work on a
wide range of mounts and you can tune PHD for your specific set up to enhance the
guiding experience.
As a best practise I recommend you only change one setting at a time and give leave
PHD for 5 minutes to assess the impact this change had. This will ensure you do not
get caught in the trap of chasing settings to fix issues.
Additionally; it is important to remember that PHD is a complimentary system to your
mount that monitors changes to apparent movement of stars, it is not a fix for other
mechanical problems such as poor polar alignment, poor balancing or poor quality
mounts.
Break Time
Before we step into how PHD interacts with EQMod would anyone like a 10 minute
break to stretch their legs, have a smoke or grab a coffee etc.?
EQMod Pulse Guiding
EQMod is a powerful tool that integrates into the ASCOM Platform allowing enhanced
control over Synta EQ mounts such as the EQ5 and EQ6.
I am not going to cover all of EQMod’s settings as we would be here all night but I will
discuss the specifics of pulse guiding via EQMod and how this differs from ST4 direct
pulse commands.
I will state up front that there are no “performance” benefits to EQMod pulse guiding
over direct ST4 commands, you do however get some additional “on the fly” control
not provided by PHD that allow you to tune your guiding for better results.
EQMod Pulse Guiding Con’t
In order to use EQMod’s pulse guiding capabilities you will need to be connected to
your mount via an EQDir cable and be controlling the mount via EQMod.
I have made a few assumptions at this point:
• You have properly aligned and balanced your mount.
• You know how to connect to EQMod and control the mount.
• You are interested in further fine tuning capabilities for your guiding.
• You want to use EQMod pulse guiding because you do not have an ST4 output to
connect to your mount.
EQMod Pulse Guiding Con’t
First and foremost to enable Pulse Guiding via
EQMod you must select the ASCOM mount from
the PHD menu bar as pictured left.
This will direct PHD to talk to ASCOM/EQMod when
you click the Telescope connect icon at
the bottom of PHD.
A this point you are
prompted for the
mount type, Select
the EQMOD ASCOM
EQ5/6 and click OK.
EQMod Pulse Guiding Con’t
Once PHD is talking to EQMod and
you are able to start guiding; there
are a number of adjustments
available in EQMod that override
PHD’s input. These are:
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Autoguider Port (ST4) Guide Rate
RA and DEC Rate
Minimum Pulse Width (ms)
DEC Backlash (ms)
Pulse Width Override
RA and DEC Gain
EQMod Pulse Guiding Con’t
As mentioned earlier ST4 guiding works using
a hard wired interface connecting your
PC/switch box/guide camera to the mount's
Autoguider Port.
The interface consists of control lines (RA+ RA- DEC+ DEC-) to control each direction
the mount can move.
In the absence of a guiding signal the RA axis will move at the tracking rate that has
been previously selected and the DEC axis will stop.
***NOTE*** With ST-4 based guiding EQMod plays no active part in the guiding
process. You can however set the rate at which each axis will move when the
associated guiding signals are sent to the ST4 Autoguider port.
EQMod Pulse Guiding Con’t
The following settings are available:
EQMod Pulse Guiding Con’t
An ASCOM Pulse guide message contains
two parameters, a Direction to move and
a Duration.
On receiving such a message EQMod will
instruct the mount to move at a preconfigured rate for the requested duration.
Once the duration expires, the RA axis DEC Axis are returned to their nominal
tracking rates - so if tracking at sidereal rate the RA Axis is set to sidereal rate and
the DEC axis is stopped. If Lunar, Solar or custom rates are in effect then it is
those rates that are applied.
EQMod Pulse Guiding Con’t
Guiding Enable Check Boxes –
The Checkbox associated with each Axis Pulse Guide Rate enables or disables the
guiding on the associated axis.
Guiding Rate –
The Pulse Guide Rate sliders can be set
between x0.1 to x0.9 of the nominal tracking
rate at increments of 0.1 independently on
each motor (RA or Dec).
The rate sliders will determine how quickly the
mount can move to correct a guiding error.
EQMod Pulse Guiding Con’t
Pulse Width Duration Override –
The “Duration Override” option allows you specify a fixed duration correction
regardless of the input by PHD. This override is only applied if the associated tick box
is checked.
Minimum Pulse Width –
The Minimum Pulse Width slider specifies the
minimum length of time a correction will be
applied and overrides any request by the
autoguider for a shorter duration.
EQMod always imposes a minimum pulse width
of 50ms as it is not practical to accurately
measure shorter periods.
EQMod Pulse Guiding Con’t
Autoguider Calibration –
PHD includes runs a self calibration routine during which a guiding pulse is initiated
and the apparent movement of the guide star is monitored to determine the guide
camera orientation and resolution.
These calibration routines will typically require a minimum movement to be achieved
and will fail if this is not achieved in a given time. This can lead to a potential
problem as the optimum settings for guiding my not deliver “fast” calibration.
If you do experience “guide star didn't move enough” type errors during autoguider
calibration you could also change the RA/DEC Rate sliders in EQMod to a higher value
to force quicker movement but please remember that the rate settings resulting in fast
calibration may not be the best for active guiding.
EQMod Pulse Guiding Con’t
The Pulse Guide Monitor –
EQMod includes a Pulse Guide Monitor tool to help you monitor the
effectiveness of your guiding and to allow you to dynamically adjust
the strength of guiding being applied if you think it is either under or
over correcting.
The Pulse Guide Monitor is accessed by pressing the EQASCOM
“DISPLAY+” button until it appears.
EQMod Pulse Guiding Con’t
Interpreting the Pulse Guide Monitor Graphs –
1. Pulse Guide Oscillations on the RA side
basically means that there are correction
overshoots. To fix this lower the RA Width Gain
settings.
2. Purely west side corrections. This means that
there is a small amount of RA drift towards the
east.
3. Purely East side corrections. This also means an RA drift towards the west.
4. ZERO Duration corrections - MAXIMDL usually issues this kind of command. It
simply means a correction abort which is perfectly normal but does not apply to
PHD.
EQMod Pulse Guiding Con’t
Interpreting the Pulse Guide Monitor Graphs –
5. Eastward drift correction. - In cases like this,
multiple corrections are issued only on one
direction with duration value getting smaller at
each correction instance. It means the
duration value issued by PHD is very small. You
may have to compensate by increasing RA
Width Gain settings.
6. North side corrections - Successive corrections on the North side would mean a DEC
drift towards the south.
7. Pulse guide Oscillations on the DEC side - Definitely a must to lower the DEC gain
settings.
8. Southward Drift Correction - Just like in #5, you may need to increase the DEC width
gain settings.
EQMod Pulse Guiding Con’t
Adjusting the Pulse Guide Gain Slider bars –
The horizontal slider bars labelled "RA Width Gain" and
"DEC Width Gain" adjust the correction durations as
issued by PHD represented as a percentage of their
original values.
This is useful when using guiding applications that do not
permit the changing of parameters once guiding has
started.
***NOTE*** Autoguiding calibration should always be
performed with the sliders at 100% gain settings.
EQMod Pulse Guiding Con’t
Focal length of guide system considerations –
The relationship between the magnifications of the guide system and imaging system
is somewhat flexible, but cannot be totally ignored.
Magnification is also referred to as "image scale" and is expressed as arc-seconds per
pixel.
A guiding system can have lower magnification than the imager because PHD can find
the centre of the guide star to much finer resolution than an individual pixel.
But if you take this too far guiding performance will suffer. I would recommend that
the image scale of the guide system be no more than two times that of the imager
(half the magnification).
Conclusion
We have covered a great deal of content, remember:
• PHD is generically set up for “all” mounts and can benefit from
tuning, the defaults are sometimes very aggressive.
• EQMod allows for fine granular “on the fly” adjustments to
guiding that PHD cannot make.
• Make changes slowly and understand the impact the change will
make to the system.
• Learn to read the monitoring tools you have available to diagnose
problems you may be facing, these can assist greatly in fixing
other faults (such as mechanical issues).
• There is an undocumented feature of PHD and EQMod called
PEBKAC.
– Problem Exists Between Keyboard and Chair, meaning if it’s
working don’t touch it, you will sometime get dud subs move
on and take the next one and don’t fiddle.
Tips
•
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Autoguiding does have it’s limitations and is not a fully closed loop
system, as such it is:
– Still important to make sure you have setup, balanced and
aligned your mount correctly.
– Your mount is stable and does not have any significant
malfunctions (such as excessive play in bearings or gears).
– Autoguiding require a stable and rigid mount so there is no
flexing between the guider and the main scope.
Ask people already doing AP for advice and guidance on how to
use Autoguiders, There is a wealth of knowledge out there.
Research before buying things to make sure you understand how
they work and that it will work for your intended purpose and
equipment.
Test your equipment at home in the backyard before you go out to
the Dark Sky site to avoid problems in the field.
Closing
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As with all thing astronomy share your ideas and findings with
others to help them along their journey
Remember you don’t need to spend a fortune to get a guiding
system running as there are many tools that are very cheap or
free to use, such as PHD.
Please support these developers by making a donation if you can
afford to, even $5 could ensure they are around tomorrow
providing free software.
Credit goes to the following for their information assisting in
making this presentation:
– Greg Marshall
– EQMod Developers
– Neil Heacock
– Craig Stark
Pray for clear skies 