Trouble-shooting and Analysis
Calibration and Mount Control ProblemsIf
you are just starting to use PHD2 or are connecting to new equipment
for the first time, you may have trouble getting calibration
done. This problem usually takes one of two forms, each requiring
nearly all cases, the "no movement" problem is caused by failures in
the mount or in the cabling and
connections. The best tool for trouble-shooting this is the
'Manual Guide' option under the 'Tools' menu, as described in the Tools
section of this help document. Simply use the directional
controls in the 'Manual Guide' window to send commands directly to the
mount while watching a star in the image display window. Use
fairly large guide pulse amounts - at least several seconds - so you
can clearly see if the mount is moving. Try to move the mount
in all four directions and verify the target star is moving by roughly
equal amounts. If the mount does not respond, you know you have
hardware or connectivity problems to resolve - nothing to do with PHD2.
If you're using a Shoestring device to connect to the mount,
watch its indicator lights to see if the commands are reaching it.
Similarly, your ST-4 compatible guide camera may have indicator
lights to show when guide commands are being received. If you're
using an ASCOM connection to the mount, be sure the COM port
assignments are correct. You can also use some of the
ASCOM-supplied tools like POTH to be sure the ASCOM driver is
communicating correctly with the mount. It is best to use the
latest version of the ASCOM driver for your mount because older
versions of these drivers might have bugs associated with pulse-guiding.
star moves during calibration but
it moves "too far" or "too little." If you've used the
new-profile wizard and have provided correct values for focal length,
camera pixel-size, and mount guide speed setting, the "step-size" used
in calibration should
already be correct. But if you've configured your profile by hand
or have changed guide speed settings in the mount, you may need
to adjust the 'calibration step-size' parameter in the 'Guiding'
tab of Advanced Settings.
The help content there describes how this parameter is used, and you
should be able to resolve the problem quickly. But if you've used
the new profile wizard and are seeing problems with "too far" or "too
little" guide star movement, the problem probably lies elsewhere.
star doesn't move enough during RA calibration, declination ('Dec')
backlash clearing, or Dec calibration. These problems
are announced by alert messages at
the top of the display window. With longer focal
lengths, small movements may even be the result of seeing
deflections, and the mount isn't
really moving at all. Dealing with this sort of problem is
Calibration Sanity-Checks and Alerts
is also possible that the calibration process will complete but PHD2
will post a calibration alert message saying that some of the results
questionable. These message do not mean
that the calibration failed or is unusable, but they are warning you
that some of the results don't look quite right. Such a "sanity check"
dialog will show an explanation
of the issue and some details of the calibration results:
There are currently 5 things checked by PHD2 as part of calibration::
of these alerts, the relevant data field will be highlighted based on
type of message. You can choose to ignore the warning ('Accept
calibration'), re-run the calibration ('Discard calibration'), or
restore your last good calibration ('Restore old calibration').
With the third option, you can defer calibration until later and
start guiding with your last good calibration data. If you see
repeated alerts on the same topic and are convinced there really
isn't a problem, you can use the 'don't show' checkbox to block
future alerts of that type. But you should be aware that the
sanity-checking used by PHD2 works well for a wide range of equipment,
and most users don't see these calibration alerts at all.
few steps (shown above) - resolving this issue can be easy assuming the
mount is actually working correctly.
Just adjust the calibration step-size downward until you get at
least 8 steps in both the west and north calibrations. If you
used the new profile wizard to set up your configuration, a good
starting value for calibration step-size will already be set. If
you find that the number of steps in RA and Declination is
substantially different, you are probably seeing evidence of
declination backlash unless you are using different guide speed
the two axes.
- Orthogonality error - the camera axes are normally computed independently even
though they should
be perpendicular. The angle calculations do not require
great precision, but if they are significantly non-orthogonal, you
should repeat the calibration. If you see repetitive alerts of
this type and the axes are significantly non-orthogonal, you'll need to
identify the problem and fix it. Common causes are
bad polar alignment, large declination backlash, or large periodic error in RA. Any of
these problems can cause the guide star to move significantly on one
axis while PHD2 is trying to measure its motion on the other axis. If
you suspect these problems, go ahead and accept the calibration, then
run the Guiding Assistant to measure your polar alignment error, declination backlash,
and RA tracking error. In other cases, the mount
may not be moving at all, and the measured
displacements of the star are just caused by seeing effects.
This sort of problem should be obvious in the calibration graph
at the left of the dialog. If the axis error is relatively small
and you are convinced the
hardware is working properly, you can avoid further alerts of this type
by setting the
option to 'Assume Dec orthogonal to RA' in the 'Guiding' tab of the
Advanced Settings dialog. But you should do this only if the error is
fairly small - otherwise, you are simply ignoring a serious problem.
- Questionable RA and Dec rates - assuming the guide speeds reported by the mount are
accurate, the measured guide rate for right ascension should be
to the declination guide rate by approximately a factor
of cosine (Declination). In other words, the apparent RA
smaller as you move the scope closer to the pole. PHD2 won't try
which rate is incorrect - it is simply alerting you that something
looks wrong with the rates. You can sanity check these rates
yourself quite simply. If you are guiding at 1X sidereal rate,
your declination guide rate should be approximately 15 arc-sec/sec;
with a guide rate of 0.5X sidereal, the declination rate would be 7.5
etc. A declination rate that is significantly smaller than the RA
rate is often an indication of substantial declination backlash.
Using a calibration that triggered this alert can lead to
over-shooting in Dec guiding because the actual guide rate is probably
larger than the measured one. To work around this problem, you
should manually clear the Dec backlash before starting calibration.
You can do this in either of two ways: 1) make sure the mount's
last slew direction was north or 2) use the hand controller to manually
move the mount north at guide speed for 10-20 seconds.
- Inconsistent results - if the calibration results are
significantly different from your last-used calibration, an alert
message will be generated. This may happen because you've made a
change in your configuration. That doesn't imply a real problem,
but you should probably consider creating a separate profile for the
new configuration. By doing so, PHD2 will remember settings
for each of your profiles, letting you switch between them easily.
If you haven't made a configuration change, you will probably
want to determine why the results are so different.
little east or south movement - The calibration process only uses the
west and north moves to compute the camera angle and rates of movement.
The east and south moves are done primarily to restore the guide
star somewhere close to its starting position. If little or no
east or south movement is seen, you may see an alert message advising
you of the situation. The calibration hasn't failed, but guiding
is likely to be impaired. The most common causes are a defective
guide cable if using ST-4 guiding or very large Declination backlash if
the alert is related to south moves.
far the most common source of calibration problems is declination
backlash, which is present to some degree in most geared mounts.
With many less-expensive mounts, however, the problem can
be severe and
can lead to poor calibration and guiding results. Consider the
example of a calibration review dialog:
first clue to the problem is found by comparing the number of steps
required for calibration on the two axes - 10 for RA but 42 for Dec.
This shows the mount was not moving consistently in
declination, probably because the backlash had not been cleared. This also explains the "wandering" behavior
of the declination points (light green) when the guide commands were
reversed from north to south. Finally, the computed declination rate is
much smaller than the RA rate even though the guide speed settings on
the two axes were identical. In fact, this would have triggered a
calibration alert dialog.
actually two problems to be addressed here. First, the
calibration result is poor and should be repeated in order to get a
more accurate measure of the declination guide rate. Second, the
mount is likely to behave badly during direction reversals in
declination even if the dec guide rate is correct. The
calibration can be improved by first manually moving the mount
guide speed for 10-20 seconds until consistent star
movement is seen in the main window. You can do this with
the 'Manual Guide'
tool or by using the hand-controller on your mount. Once this is
done, most of the declination backlash in your mount should have been
overcome. You can then repeat the calibration procedure
and probably get a declination guiding rate that is more
The underlying backlash problem generally requires some
to the mount. If the mount isn't using a guide speed close to
1x sidereal, you can probably get an immediate improvement by
increasing the mount guide speed. You can also try using a
PHD2 backlash compensation setting,
but this is not likely to work well if the backlash is large -
more than 3 seconds, for example. If you can't correct
backlash or reduce
it to manageable levels, you should consider choosing uni-directional
guiding for declination. To do this, you determine
which way the mount drifts due to polar alignment error and tell PHD2
to guide only in the opposite direction (see Uni-directional guiding). This is controlled by the 'Dec
guide mode' control on the'Algorithms' tab of the Advanced Settings dialog.
For example, if the
mount tends to drift north overall, restrict guide commands to
south-only. This is not an ideal solution, obviously, but you can
still use reasonably long exposures and achieve good guiding results
- many imagers choose to use this approach.
If you have an unusual circumstance, such as a mount with no
declination control at all, you can set the 'Dec guide mode' choice to
Validating Basic Mount Control - the Star-Cross Test
If you are having repeated
problems getting calibration to complete without alert messages, you
should run a very simple test to see if the mount is responding to
guide commands. This test basically mimics what is done during
calibration, but it is more direct and can give you a better feel for
what's going on. We'll call it the "star-cross" test. The
idea is to open the shutter on the main imaging camera, then send guide
commands that should cause the stars in the field to trace out a
distinctive cross pattern. In other words, you want to get an
image that looks something like this:
The angular orientation doesn't matter, that's just a function of how you
have the guide camera rotated. What is important is that the
lines in the cross are perpendicular and have roughly equal lengths in
each of the four directions relative to the starting point in the
center. If the image you get doesn't have this approximate
appearance, guiding will either be impaired or perhaps impossible.
For example, consider the following poor result:
can see the star has moved along only one axis - only
in right ascension in this example. The declination guide
commands sent to the mount did nothing at all. Until this is
fixed in the mount, you won't be able to guide in declination at all
and will have to disable declination guiding to even complete a
calibration. There are many other permutations of bad
results, each suggesting a particular problem in the mount, the guide
cable, or much less likely, the ASCOM driver for the mount. You
can safely assume it has nothing to do with PHD2.
Here are the steps for running the test:
can use different pulse lengths if you want, perhaps using smaller
values to confirm the mount will respond to them. Just be sure
the total exposure time on the main imaging camera is longer than the
total of guide durations plus a margin for error. On most mounts,
the star will not return to its exact center because of some
declination backlash - you can see that in the first example image. But
it should be fairly close or you'll need to look more carefully at how
much declination backlash you have in the mount. PHD2 also has a star-cross test tool, described here: Star-cross Tool. You can use that to automatically perform the test steps described in 1-5 above.
- Set the mount guide speed to 1X sidereal. Bring up
the 'Manual Guide' tool in PHD2 and choose an initial pulse size - start with,
say, 5 seconds.
- Start a 60 second exposure on the main camera.
a 5-second pulse west, then two 5-second pulses east, then a final
5-second pulse west. This should return the star to its
approximate starting position. You should wait about 5
seconds after sending each guide pulse to give the command time to
complete before sending the next pulse.
- Now send a 5 second pulse north, then two 5-second pulses south, then a final
5-second pulse north. This should again return the star to its starting position.
Wait for the main camera image to download and see what you get.
One benefit to
using this test is that it reduces things to the absolute basics: will
the mount move as directed or not. It has nothing to do with PHD2
guide settings because they aren't involved in the test. You may
find it helpful to use the test results to communicate with the mount
manufacturer or other users who understand your type of mount and its typical problems.
Measuring the Mount's Behavior
If you're having trouble
getting decent guiding results, your first instinct will probably be to
try making wild changes to the guiding parameters in the hope of
finding a magic solution. This almost never works, and you're
more likely to just make things worse. If the default parameters
from the new-profile-wizard aren't producing reasonable results, the
fault is probably with the hardware and you'll need to determine the
underlying cause. Once you understand the cause, you can probably
improve your guiding results even if no actual repairs can be made -
but understanding the underlying problem is important. To
understand what the mount is doing, perform the following steps:
1. Use the new-profile-wizard to create a new equipment profile for the test, being sure the guide scope focal length and camera pixel size are correct. Don't guess at them, look them up if you aren't sure.
Use an ASCOM connection to the mount if one is available and set the
mount guide speed to 0.5x - 1x sidereal. Disable any backlash
compensation you have in the mount.
Use 1-2 second exposures and let PHD2 auto-select a guide star near Dec=0 with the scope pointing at least
45 degrees above the horizon to minimize seeing effects.
4. Run the
Guiding Assistant for 10-15 minutes and apply whatever recommendations
it makes, particularly with respect to min-move values. Let it
measure your declination backlash. You may need to use a large
tracking region to avoid losing the guide star during this part of the
process - just be sure there aren't multiple stars in the tracking
rectangle. The backlash test will move the star a long distance
north, so choose a guide star that is nearer the southern edge of your
camera frame to give yourself plenty of room.
Watch how things are going during the GA session. If you bump the
mount or something really unusual happens, stop the test and then
restart it. The goal is to measure the performance when things
are running normally.
6. Do not change any of the guide parameters beyond what is recommended by the Guiding Assistant.
Take a careful look at the results shown in the Guiding Assistant
table. Each entry in the table can tell you something useful
about the mount's performance. These results are also written to
the guiding log, so they are available for later analysis.
If you got calibration alert messages in step 3, you should probably
remedy those problems before proceeding. Guiding with a bad
calibration is not likely to produce good results. Also, if your
polar alignment error is 10 arc-min or more, you should improve on that
and then repeat the above steps.
9. Let PHD2 guide for another 10-15
minutes, just letting it run as long as there aren't gross errors from
wind or other "mistakes." Do NOT change any of the guiding parameters while this is being done.
you want to analyze the results yourself, use the PHDLogView tool and
the tutorial on Analyzing PHD2 Guiding Results. You should also
consult the document on PHD2 Best Practices. All of these
references are available on the OpenPHDGuiding.org web site under the
'News' tab. If you'd like some help understanding the results,
post both the guiding and debug log files on the OpenPHD2 Google forum
and we'll be glad to help you out.
Display Window ProblemsNew users often complain
that the image displayed in the main window is extremely noisy or is
almost all-white or all-black. Assuming the camera is
functioning and actually downloading images, the display issues are
often caused by the absence of any usable stars in the frame. For
example, trying to test the camera indoors or in daylight will almost always create
these conditions. The appearance of the image display window in
these situations provides no useful information and should be
discounted. PHD2 uses an automatic screen-stretching function
that is intended to help you see real stars under a nighttime sky.
When no stars are present, the display will be stretched to show
the range of minimum-to-maximum brightness values of whatever is in the
frame - which is often nothing at all. This is usually what
causes the noisy/all-white/all-black display results. You may
also encounter display problems if the guider is not well-focused.
Focusing the guider can be a tedious process
but it's critical to getting good guiding results. A good
technique is to start with a bright but unsaturated
star and try to reach focus with that. Then move to successively
fainter stars to fine-tune the focus position using the PHD2 Star
Profile tool to measure the size of the guide star. Good results
can also be obtained using a Bahtinov focusing mask or focusing tools
in other applications. It doesn't matter what you use so long as
you reach a good focus position.
Hot-pixel and Star-Selection ProblemsWith most guide cameras, you can encounter problems where
clumps of hot pixels are mistaken by PHD2 as guide stars. This
can be especially annoying if you're using automation tools and
the 'auto-select' guide star selection is mistakenly choosing hot pixels. For many cameras, a
simple dark frame will suffice for reducing or eliminating hot-pixel
problems, and dark frames should always be used as a starting-point.
But for other cameras, you will need to build a bad-pixel map and
update it as necessary when you see changes in the locations and sizes
of defective pixels. Camera sensors change over time and may
react to changing temperatures, so bad-pixel map maintenance is a small
task you should be willing to perform. Step-by-step instructions can
be found in the Bad-pixel map
chapter of this document. These problems are different from
transient hot pixels, which can be caused by cosmic ray strikes on the
sensor. Although cosmic ray hits can disrupt guiding, there's
really little you can do about them.
the recommended practice is to let PHD2 choose the guide star
("auto-select"), you should use the available UI controls to help PHD2
do the best possible job. The Minimum-HFD property on the Guiding
tab of the Advanced Settings dialog is probably the most effective tool for
avoiding hot-pixel selection. You should set its value to
allow use of the smallest and faintest real star your setup can
produce. You should use the Star Profile tool to measure a
reasonable sample of legitimate guide stars for your system. Then
set the Minimum-HFD value to accept those stars while rejecting smaller
bright spots that are really just sensor defects. At the other
end of the scale, you should also specify the brightest
pixel value your system will deliver - the ADU value that represents
saturation. By doing this, you will prevent PHD2 from rejecting
stars that have a flattened profile but aren't really saturated. The
saturation control resides on the Camera tab of the Advanced Settings dialog and
is part of a control group labeled 'Star Saturation Detection'.
Choose the option for 'Saturation by Max-ADU value', then set the
value for your system. If you have an 8-bit camera, saturation
will be around 255, while a 16-bit camera will saturate around 65000
ADUs. If you don't know the correct value, you can just point the
scope at a bright star, use a multi-second guide camera exposure, and
again look at the Star Profile window. One of the things you'll
see in that window is the 'Peak Value' - that's the ADU value for the
brightest pixel and the one to use for setting the saturation
point. Using both of these controls is likely to produce much
better results for PHD2 guide star selection.
Restoring a Working BaselineDespite advice to the contrary, you may have made rapid, uninformed
changes to your guiding parameters only to find the performance stayed
the same or even got worse. Before proceeding, you should restore the
settings to their default values. If you used the
new-profile-wizard to build your profiles, the parameters will have
been set based on the specifics of your configuration, and they are
likely to be pretty close. If you encounter significant
guiding problems using those settings, you are probably having
issues with the mount or other hardware. Blindly changing guiding
parameters almost never solves these problems and quite often makes
things worse. You have several options for restoring the settings
to their default values:
- On the 'Algorithm' tab of the
Advanced Settings dialog, you can individually reset parameters by looking at
the tool-tip for each field. Hover your mouse cursor over the
field and the default value will be displayed. Note that this is
not accurate for the min-move settings, which depend on your image
scale. This approach is best when you want to restore only a few
- Click the 'reset' buttons on the 'Algorithm' tab for
the selected RA and Dec guide algorithms. This is the recommended
approach for resetting all the guiding parameters. The min-move
settings will be reset to the values originally calculated by the
new-profile-wizard. If you subsequently adjusted those settings
by running the Guiding Assistant, you should repeat that process.
- Run the new-profile-wizard, accessed by clicking on the 'Manage Profiles' button in the 'Connection' dialog.
Use the same camera and mount choices you already have and give
the profile a new name. If you want to re-use the dark library
and bad-pixel map from the old profile, connect to the new profile and
use the 'Darks' menu to import those files from the old profile.
Once you are satisfied with the new profile settings, you can
delete the old one.
Camera Timeout and Download ProblemsIn
some cases, you may experience problems where guider images aren't
downloaded or displayed. In extreme cases, this may even cause
PHD2 or other camera-related applications to be non-responsive (i.e. to
"hang"). Again, this is almost always due to hardware, camera
driver, or connectivity issues, with one of the most common
culprits being a faulty USB cable or device. It is highly
unlikely to be caused by an application like PHD2,
so you should begin
your investigation at the lower levels of the system. You can start by
confirming that the guide camera is working - try using a short, direct
cable from the camera to the computer and taking exposures with
the native or test application that came with the camera.
camera is functional, you can start looking at USB
hubs and cables, swapping them one at a time to see if you can isolate
the problem. It's worth remembering that we work in
environment while doing our imaging, and many of the components we use
are not designed for cold, outdoor conditions. So something that worked
just last week or last month may no longer be reliable.
help detect and work around these kinds of problems, PHD2 uses a camera
timeout mechanism. This timeout value is set in the Camera tab
of Advanced Settings. and uses a default value of 15 seconds. This means that PHD2 will wait up to 15 seconds after the completion of the exposure
to receive the image from the camera. This is a very generous
amount of time and should work well for most cameras.
However, some cameras are known to create problems by
making large bandwidth or power demands on the USB subsystem.
If you are getting timeouts of this sort and are convinced the
camera is working properly, you can increase this timeout value. You can even change it to a very
high number - even 1000 seconds or more - so that timeout errors are never shown. Doing so leaves you
vulnerable to apparent hangs in the user interface and erratic guiding
behavior, but it is a choice you can make for yourself. A larger
value for the timeout will not create extra delays during normal camera
operations - once the image is downloaded from the camera, the timer is cancelled and guiding will proceed immediately.
Here are some diagnostic steps that can help you isolate these kinds of problems:
Common sources of camera timeout problems are the USB subsystem on the host
computer, incompatible USB3/USB2 connections, damaged or low-quality USB
cables, or flakey camera drivers. You
will probably need to work through a number of scenarios to see what your
problem is. Fortunately, this can usually
be done in the daytime by putting the cameras in continuous-exposure mode and
letting them run. Start by connecting just the imaging camera and the guiding camera because
these will be the two heaviest users of the USB subsystem. To start, there are often problems when a
USB-2 camera is connected to a USB-3 port on your computer. Those things are supposed to be
backward-compatible but that’s only at the hardware level – the driver
implementations can be adversely affected. There are two areas to look at: 1) USB
traffic and bandwidth and 2) power delivery to the cameras. Your main imaging camera probably has its own
power supply but other devices like the guide camera may be powered via the USB
cable. If that’s the case for
you, you may want to try using a powered USB hub to deliver power to the
camera. It’s also best to use
high-quality USB cable with a 24AWG power conductor and eliminate long USB
cable runs and USB extenders. If
your problem seems to be with USB traffic, there may be other things you can
sure your computer is running from AC power and that the OS
can't disable the USB ports for power conservation. Don't run
other resource-intensive applications while trying to image.
- Bin the guide camera to reduce the size of the downloaded guider images
- Adjust the USB usage limit of the camera if the camera driver supports
- Use sub-frames in PHD2
- If you’re running Windows, you can use a Microsoft tool to
map out how the various USB ports are tied to the USB controllers in the
computer. Then you can try to
isolate the two cameras on separate USB buses.
- Try using a different camera driver (e.g. an ASCOM driver) if one
Poor Guiding Performance Once
you've gotten everything running, you will probably get reasonably good
guiding results almost immediately. You will have to decide what
"good enough" means, and everyone's standard is likely to be different.
But if you find your imaging results are not acceptable
because the stars are streaked or elongated, you'll need to take a
systematic approach to correcting the problems. It is often
tempting to just start blindly adjusting the various guide parameters
in an effort to make things better. There is nothing wrong with
adjusting the parameters - that's why they're there - but it should be
done carefully based on an understanding of what they do and what problem you're trying to solve. The
PHD2 default settings are carefully chosen to produce reasonable
results for most amateur equipment and locations. Optimal
settings are entirely dependent on the image scale, seeing conditions,
and behavior of your specific mount. In other words, they are
unique to your situation - there is no magic "red book" of correct
guiding parameters, and settings you get from other users may be
completely irrelevant to your situation. If you got started by
using the new-profile-wizard, the default settings will already be
tuned fairly well to match your image scale. By using the Guiding
Assistant, you can get more specifics about your situation - how the
seeing conditions look and how you might adjust the minimum-move
settings to avoid chasing the seeing. You can also use either the
Guiding Assistant or the Manual Guiding tool to see how much backlash
is present in your mount, something that can be important to understanding your declination guiding results.
Achieving the best possible guiding performance can be a
complex task and not something that can be covered here. However, you
can get help on the web from a variety of sources, with the document by
Craig Stark being a very good place to start:
will sometimes display alert messages at the top of the main display
window. These generally show error or diagnostic information that
warrant your attention. During normal operation, you probably
won't see any of these, but if you do, this section can help you decide
what to do about them.
Dark-library and Bad-pixel Map Alerts
"Use a Dark Library or a Bad-pixel Map"
- using a dark library or bad-pixel map reduces the likelihood that
PHD2 will mistakenly identify hot pixels or some other image defect as
a star. If you choose to ignore this message, you'll be
vulnerable to situations where PHD2 inadvertently switches from the
guide star to a hot pixel and no longer guides correctly.
- dark frames and bad-pixel maps must match the format of the sensor in
the camera being used. If you've changed the camera in an
existing profile, the existing dark/bpm files will not be usable and
you'll see this alert message. To avoid seeing the message,
instead create a new profile when you change cameras. You'll still need
to shoot new darks or bpms, but you can keep the old files for use with
the original camera. In very unusual
circumstances, you may see this message when either the
driver or PHD2 code for handling the camera has changed. You might
format-incompatibility alert message if you have an old dark library
that has somehow accumulated frames with different sensor formats.
any of these cases, you should rebuild the dark library or bad-pixel
map from scratch - more information can be found here: Dark Frames and Bad-pixel Maps
you first connect to a mount, camera, or other ASCOM-controlled device,
you may see an alert message saying that a required capability is not
supported by the driver. One example would be lack of support for
pulse-guiding by an ASCOM telescope/mount driver, something that can
occur with outdated drivers. In these situations, your only
recourse is to update the ASCOM driver. These drivers are
generally available from the ASCOM web site or, in some cases, from the
device manufacturer. As
a rule, the best practice is to use the latest versions of these
drivers so you don't encounter problems that have already been fixed.
You might also see other alert messages associated with the ASCOM driver for the mount:
"PulseGuide command to mount has failed - guiding is likely to be
ineffective." This is usually caused by a bug or timing
sensitivity in the ASCOM mount driver, and there is generally no way to
know if the guide command was executed properly or not. If
you rarely see the alert and your guiding results are acceptable,
you can probably ignore it. Despite the alert condition, PHD2
will continue to issue guide commands, so you don't need to take any
immediate action. If you see the alert frequently, you should
send us your debug log so we can understand the details of the problem
and possibly help you describe it to the author of the ASCOM driver.
"Guiding stopped: the scope started slewing." This is pretty
self-explanatory, but the determination that the scope was slewing is
something reported to PHD2 by the ASCOM mount driver. Whether it
was actually slewing isn't known to PHD2. Assuming you didn't
mistakenly slew the scope with guiding active, there is probably a
timing problem in the driver. If you want to sidestep the problem
temporarily, you can disable the logic to check for slewing - go into
the 'Guiding' tab of the Advanced Settings dialog, and un-check the box that says
"Stop guiding when mount slews." This will let you continue
guiding, but the results might be suspect. The debug log should
provide the details needed to describe the problem to the author of the
Camera Timeout Alerts
Alert messages associated with camera timing/timeout problems are discussed above: Camera Timeouts
A number of alerts may appear during the mount calibration process. These are described here: Calibration Alerts
Maximum-Duration Limit Alerts
normal guiding, you may see an alert message saying that your settings
for maximum-duration limits in RA or Dec are preventing
PHD2 from keeping the guide star locked. If you've decreased
these parameters from their default values, you should restore them to
their default values. However, if the limits are well above one
this alert probably indicates you've encountered a mechanical problem
that needs to be corrected. In the simplest cases, you may have
suffered a cable snag, wind gust, mount bump, or other external event
that caused the guide star to move by a large amount. In such
cases, you simply need to correct the problem if you can and proceed
with guiding. But in other cases, the alert may be triggered by a
steadily growing guide star displacement that is not being corrected at
For example, if PHD2 can't move the mount correctly in either the
north or south directions, the cumulative uncorrected error will
eventually reach a point that triggers the alert. Or you may be
encountering "runaway" Dec guiding because the setting for 'reverse Dec
output after meridian flip' (Advanced Settings/Guiding tab) is incorrect.
These sorts of
problems will require some diagnosis and simply
increasing the maximum-duration limits will not help.
sort of problem isolation or tuning will invariably require use of
the PHD2 log files. Both are formatted for straightforward
interpretation by a human reader, and the guide log is constructed to
enable easy import into other applications. As mentioned in the
'Tools' section, applications such as PHDLogViewer or Excel
be used to visualize overall performance, compute performance
statistics, and examine time periods when guiding was problematic.
With Excel or similar applications, simply specify that the guide
log uses a comma as a column separator.
Guiding Log ContentsThe
contents of the guiding log will continue to evolve as new capabilities
are added. But the basic content is stable, and considerable care
is taken to not "break" applications that parse it. If you wish
to analyze the log yourself, the following information will be helpful.
The PHD2 guide log will contain zero or more sequences of
calibration and zero or more sequences of guiding. Each of these sections has a
header that provides most of the information about the guiding algorithms being
used and the internal parameters used by PHD2 for guiding. At the start of either a calibration run or
a guiding sequence, the last line of the header information defines a set of
column headings. The meanings of those
columns are shown below:
- dx, dy
are offsets from the starting position, in pixels, in the camera coordinate
- x, y are the camera x/y coordinates of the guide
star at the end of each calibration step
- Dist is the total distance moved in the camera
coordinate system (dist = sqrt(dx*dx + dy*dy).
This is the value used by PHD2 to compute the calibration parameters
- dx, dy are the same as for calibration - offsets
from the "lock position" of the guide star in the camera coordinate
- RARawDistance and DECRawDistance - these are the
transforms of dx and dy into the mount coordinates - in other words, they use
the arbitrary angle of the guide camera to map from X/Y on the camera to RA/Dec
on the mount
- RAGuideDistance and DECGuideDistance - these are
the outputs from the various guiding algorithms. The guide algorithms operate on the
"raw" distances and decide how far, if any, the telescope position
should be adjusted in each axis. For
example, with a "minimum move" parameter set, the "guide"
distances can be zero even when the "raw" distances are non-zero.
- RADuration, RADirection, DECDuration, DECDirection
- these are the values determined by the two "guide" distances
above. The "durations" are the
lengths of the guide pulses, in milliseconds, needed to move the mount by the
distances specified by RAGuideDistance and DECGuideDistance
- XStep, YStep - step-adjustment durations for the
adaptive optics device if one is being used
- StarMass - a brightness measure of the guide
- an internal "star-detection ratio" used by PHD2 - essentially a
measure of how well the star can be distinguished from the sky
- ErrorCode - an integer value representing the quality of the guide star measurement:
- 0 - no error
- 1 - star is saturated
- 2 - star has low SNR
- 3 - star mass is too low for accurate measurement
- 4 - star has drifted too near the edge of the frame
- 5 - star mass has changed beyond the specified amount
- 6 - unexpected error
All distance values are in units of pixels. The header for the guiding section will show
the image scale as it is known by PHD2, and that can be used to scale the pixel
distance values into units of arc-seconds if desired.
you encounter application problems that are specific to PHD2, you
are encouraged to report them to the open-phd-guiding Google group: https://groups.google.com/forum/?fromgroups=#!forum/open-phd-guiding.
Obviously, the more information you can provide, the more likely
we will be able to resolve the problem. Using the following
guidelines will help in that regard:
- Try to reproduce the
problem - if we have a clear set of steps to follow, we are more likely
to find a solution quickly. If you can reproduce it, try to
reduce things to the minimum number of steps. Remember, we won't
have your hardware or computer environment when we try to reproduce it
- Try to be complete about describing your configuration - operating system, equipment types, PHD2 version, etc.
debug log from the session in which you encountered the
problem. You can find the debug log in the PHD2 folder in your
Documents folder. If you can't reproduce the problem, try to
time of day when you first saw it - this could help us find evidence in
the debug log without having to sift through hundreds of lines of
output. The 'Upload log files' function on the 'Help' menu can help you find and upload the log files.