Tools and Utilities
Manual Guide
Auto-Select Star
Calibration Details
PHD2 Server
Dithering Operations
Logging and Debug Output
Polar Alignment Tools
Lock Positions
Comet Tracking
Guiding Assistant
Equipment Profiles
Ask for Coordinates Aux Mount
Simulator Parameters
Multiple Program Instances
Keyboard Shortcuts
Software Update
Manual Guide
If you are encountering calibration
problems, you will probably want to be sure that PHD2's
commands are
actually getting to the mount. Or you may want to nudge the mount or
experiment with manual dithering. In the 'Tools' menu, click on
'Manual
Guide' and
a dialog will appear to let you move the mount at guide speed in any
direction. If you have an
adaptive optics device attached, you'll see separate move buttons for
both the AO and the secondary mount. Each time you press the button, a pulse of the duration
specified in the 'Guide Pulse Duration' field will
be sent. The default value is the 'calibration step-size' set in
the Advanced Settings dialog. If you are debugging mount/calibration
problems in the daytime, listen to (rather than watch) your mount to determine if it is getting
the commands from PHD2. The idea here is just to figure out if the
mount is responding
to PHD2's
signals. You won't be able to see the mount move (it's moving
at guide speed)
but you may be able to hear the motors. Other options include watching
the
motors and gears or
attaching a laser pointer to your scope and aiming it at something
fairly far away (to amplify your motions). A better approach
for nighttime testing is to run the "star-cross" test described here.
Dithering
is used primarily with image capture or automation applications using the PHD2 server interface. However, you can do
manual dithering or experiment with dither settings using the controls
at the bottom of the dialog. The 'dither' amount field at the
left controls the amount the mount will be moved , in units of
pixels. You can scale this amount - i.e. multiply it by a
constant - by using the 'scale' spin control to the right. These
two controls establish a maximum amount of movement that will be used
for dithering - the product of 'scale' X 'dither'. When you click
on the 'Dither' button, PHD2 will move the mount by a random amount
that is less than or equal to the limit you have set, in one of the
north/south/east/west directions. The 'RA Only' checkbox will
constrain the dither adjustments to only east or west. Obviously,
if you are doing a manual dither in this way, you'll want to be sure
your imaging camera is not in the middle of an exposure.
Auto-Select Star
Automatic guide
star selection can be accomplished in several ways. The simplest
is to click on the 'Auto-Select Star' icon in the main window,
next to the 'Guide' icon. But it can also be triggered by using
the keyboard
shortcut of <Alt>S or by clicking on the ' Auto-select star' item
under the 'Tools' menu. Taking any of these actions tells PHD2
to scan the current guide image
and identify a star most suitable for guiding. PHD2 will try to select
a star of sufficient brightness that is not
saturated, has sufficient size, and is not too near another star nor too close to the edge of the
frame. The
selected star may appear fairly dim on the screen, but that's usually
not important - just adjust the gamma slider on the main window.
The auto-select function will almost always do a better job than
you can just looking at the display. In many cases, a star
you choose interactively is at or near saturation and will produce
sub-par results. You can use the Star Profile tool
to examine the properties of the selected star, however it was chosen.
To get the best results from Auto-Select, you should
definitely use either a bad-pixel map or dark library and specify a
Min-HFD value (Advanced Settings/Guiding tab) to reduce the
likelihood of PHD2 mistakenly choosing a hot pixel. It also works
better if you set the option to measure saturation by Max-ADU value
(Advanced Settings/Camera tab), assuming you know or can determine the
maximum ADU value of your camera. For example, a 16-bit guide
camera will have maximum ADU values approaching 65000.
To
de-select the star and continue looping exposures, just shift-click on
the 'Auto-Select Star' icon or shift-click anywhere in the image
display window. This can be useful if you're using sub-frames and
want to return to a full-frame view of the guider images.
Calibration Details
Most of the calibration-related windows, including calibration sanity-checks, will open a window that looks something like this:
The
first thing to look at is the graph to the left, which shows what star
movements resulted from the guide pulses that PHD2 sent during
calibration. The lines represent the RA and Dec guide rates that
were computed as a result of the calibration, and these lines should be
roughly perpendicular. The data points will never be perfectly
aligned, but they should not have major curves, sharp inflections,
or reversals in direction. Particularly with longer focal length scopes, the
points will often show considerable scatter around the lines, but this
is normal. The solid points (west and north pulses) are used to
compute the RA and declination rates, while the hollow points show the
"return" paths of the east and south moves. These can help you
see how much fluctuation occurred due to seeing and also whether there
is a significant amount of backlash. If you are using the
"fast-recenter" option in the Advanced Settings, there may be many
fewer points shown in the east and north paths. The tabular
information to the right
shows what was known about the pointing position of the scope and the
various ASCOM settings that relate to guiding. If you are not
using an ASCOM mount and don't have an "Aux mount" specified, some of
this information will be missing. The table will also show
the expected guiding rates for a "perfect" calibration using
the same sky position and guide speed settings you used. You will
almost never achieve these ideal values, and you shouldn't worry about
them unless your values are very different. If you didn't see an
alert message when the calibration completed, your results are probably
good enough. If you want to re-use a calibration for an extended
time, it is probably worth a few extra minutes to check this
information and confirm that the calibration went
reasonably well and produced sensible results. Bad calibrations
can occur even for very experienced imagers using high-end mounts, so
it is good to check.
If you are having consistent problems getting alert-free calibrations, you should review the material in the trouble-shooting section .
Other Calibration-Related Menu Options
Calibration data are saved automatically each time a calibration sequence completes
successfully. The use of the calibration data has been described
elsewhere (Using PHD Guiding),
including options for restoring calibration data from an earlier
time or "flipping" it after a meridian flip. You access these
functions using the 'Modify Calibration' sub-menu under the 'Tools' menu. Two other
calibration-related items are shown there, namely the options to
clear the current data or to enter calibration data manually. The
"clear" option accomplishes the same thing as the 'Clear calibration'
checkbox in the Advanced Settings dialog - it will force a recalibration
whenever guiding is resumed. The 'Enter calibration data'
option should be used only under
very unusual circumstances and only if you're sure you know what you're
doing; but it is available as a matter of completeness. If you
click on the 'Enter calibration data' item, you'll see a dialog box
that allows input of relatively low-level calibration data. This
data might come from a much earlier session, perhaps extracted from the
PHD2 guiding log file.
Keep in mind, if you are using an ASCOM driver for either the
'mount' or 'aux mount' connections, you should have little need for
these calibration data controls.
PHD2 Server
PHD2 supports third-party
imaging and automation applications that need to control the guiding
process. Sequence Generator Pro is probably the most popular of
these but there are numerous others. By using the PHD2 server process, image capture
programs can control dithering between exposures or suspend guide
exposures while the primary imaging camera is downloading data.
To use these capabilities with a compatible application, you
should click on the 'Enable Server' option under the 'Tools'
menu. The PHD2 server interface is quite extensive, and it's possible
for an application to control most aspects of PHD2's guiding operations. Documentation for the
server API is available on
the PHD2
Wiki.
Dithering
The
primary purpose of dithering is
to make post-processing easier by removing some kinds of fixed-pattern
noise in the images, especially hot pixels. This is primarily
a function of the camera you're using and to a lesser extent, the
sophistication of the post-processing software. For imagers
with temperature-regulated, low-noise cameras, dithering is mostly
a convenient way to eliminate hot pixels that aren't getting
removed by the dark frames. Hot pixel positions change as sensors
age, so dark libraries don't usually correct for all of them. Those hot
pixels can also be removed in post-processing, but that becomes
tedious if there are lots of them. Dithering can help with some
other kinds of sensor behavior such as
column defects, and it's particularly helpful if there is no
temperature regulation on the sensor and therefore no good way to use a
dark library. DSLR imagers often use aggressive dithering to
handle the substantial fixed-pattern noise usually present in those
sensors. In the PHD2 implementation, automated
dithering is accomplished through the server interface, so make sure
you have 'Enable Server' checked under the 'Tools' menu. You
first specify a maximum dither size you want to use during the
guiding session - this will be set in your imaging application.. When
that application issues a dither command, PHD2
uses a random number generator to decide how large the dither will
actually be for that command. The actual dither mount will be
> 0
and <= the maximum amount allowed. Pseudo-random
dither amounts like this are used to insure that dithering doesn't
follow a simplistic back-and-forth pattern or shift the frame back to a
location where it has
previously been. But for some of the applications that do PHD2
dithering, you
can't specify the maximum amount directly - you are perhaps limited to
choices like small/medium/large and the max dither amounts will have
preset values. For that reason, PHD2 has a dither scaling
parameter in the 'Global' tab of the Advanced Settings dialog. It is
basically a multiplier term that lets you adjust the range of dither
amounts that are possible. So a scale factor of 1 doesn't change
the
preset value at all, a value of 10 multiplies it by 10X, etc. If
you're using an app that lets you specify the maximum amount directly
(e.g. PHD_Dither), you should leave the dither scale set to 1.0.
Otherwise, you can adjust the scale factor if you aren't
happy with the overall range of dithering you're getting with one of
the small/medium/large type imaging apps.
There are typically
two costs associated with dithering: 1) the extra time and uncertainty
required for "settling" and 2) the need to crop the final stacked frame
in order to remove the low-signal margins. Settling is the term
used for a period of stabilization after the mount has been moved by a
dither command. The imaging app that starts the dither will also
decide when the guiding has stabilized enough to continue
imaging. The app can let PHD2 determine this by specifying the
settling parameters or the app can do the calculations itself.
You'll need to look at your imaging/dithering app to see what control
you have over this process. If the app uses the latest PHD2
server interfaces, it can specify a settling requirement that might
look like "guiding errors must be less than 1.5 pixels for a period of
at least 10 seconds." This is a process that can consume some
time, depending on how tight the requirements are for settling.
It is likely to take more time if you are dithering in declination and
the dither forces a change in direction. Most mounts have some
declination backlash, so it can take a number of guide commands to get
the mount moving in the right direction, and then more time for the
process to converge on the new target location for the guide
star. That's why PHD2 also offers the option to dither only in
right ascension. Again, this is an option on the 'Global' tab,
right next to the dither scaling parameter. Mounts with
substantial Dec backlash or setups that need a large amount of
dithering can benefit from using the "spiral mode" (. With this
approach, neither the dither size nor the direction is
randomized. Instead, PHD2 issues a fixed-size dither while
forcing the direction to trace out an expanding spiral around the
original lock-point.
If
your mount has a substantial amount of declination backlash in the
mount, you may be guiding in only the north or south Dec direction.
If PHD2 receives a command to dither in declination while you're
operating in this mode, it will temporarily allow guiding in both Dec
directions until the dither and settling are completed. It will
then revert to the original north/south-only guiding mode. If you
don't want this behavior, you should restrict dithering to 'RA-only'.
All of the PHD2 dither controls are contained on the 'Global' tab
of the Advanced Settings dialog.
Logging and Debug Output
PHD2 automatically creates two types of log files: a debug log and a
guiding log. Both are very useful for different reasons.
The guide log is intentionally formatted to
allow easy interpretation by either a human reader or an external
application. For example, the PHDLogView application (not
part of the PHD2 release) can produce a variety of graphs and summary
statistics based on data in the PHD2 guide log. But the log can also be easily imported into
Excel or other applications for analysis and graphing.
When importing into Excel, just specify a comma as a
column separator. The
debug log
has a complete record of everything that was done in the PHD2
session, so it is very helpful in isolating any problems
you have. It also employs a human-friendly (albeit verbose)
text format, so it's
not
difficult to examine the debug log to see what happened. If
you
need to report a problem with the software, you will almost certainly
be asked to provide the debug log file. If you have neither log
file available, you are unlikely to get any help.
The location for the files is controlled by the 'Log
File
Location' field in the 'Global' tab of the 'Advanced Settings' dialog. By default, log
files
are stored in the OS-specific default directory for user documents.
In Windows, for example, the files will be stored in a 'PHD2'
sub-folder in the "Documents" directory. This may not be a
convenient location, so you can specify a different folder using this
edit field. In order to prevent excessive accumulation of log
files, PHD2 automatically removes debug logs that are more than 30 days
old and guide logs that are more than 60 days old. If you want to
retain the files for longer periods, you should move or copy them to a
different folder location, one not used by PHD2.
To
simplify the automatic log upload process (see below), log data is
grouped by "imaging day", defined to be a 24-hour period beginning at
09:00 am local time. This means that all the PHD2 executions on
the same imaging day will write guiding and debug log data into the two
log files for that imaging day. Logging is always active
regardless of what was done (or not done) during the time that
PHD2 was running.
In some unusual cases, you may need to capture guide
camera images, usually to support debugging and problem resolution.
This can be done by clicking the 'Enable Star Imaging Logging'
menu item under the 'Tools' menu. The resultant image files will
be stored in the same location as the other log files. The format
of these image files is controlled from the 'Global' tab of the
'Advanced Settings' dialog. If you are trying to document a
problem you're having, you should choose the 'Raw Fits' format for
maximum flexibility.
Automatic Log File Upload
If you need help using PHD2 or improving your guiding results, you'll want to post a request on the Open-PHD-Guiding
forum (https://groups.google.com/forum/#!forum/open-phd-guiding).
Your question should be accompanied by the PHD log files
associated with the guiding session you're talking about. Please
do not edit, trim, or rename the log files. To make uploading easier,
PHD2 has a built-in function to select, compress, and
automatically upload the relevant log files. That function is
located on the 'Help' menu. You'll see a dialog box that shows
all the available log files, including their timestamps and duration:
Just
select the files you want and start the upload process by clicking on
'Next'. Please be careful to look at the 'Session Start' and
'Duration' columns to be sure the log covers the time period you're
interested in. PHD2 creates guide and debug log files every time
it's run, so some of the log files will be nearly empty - don't upload
those. If PHD2 is generally working for you but you can't
interpret the guiding performance or you want to improve it, you can
start by just uploading the guide logs. But if you're having
trouble with camera or mount connections or otherwise can't get PHD2
running, you should also include the matching debug log file. Be
selective about the files you choose - just the files for the session
you were having trouble with. When the upload process is
complete, you'll see another window that gives you a link to the files:
You
need to capture or record that link so it can be included with the
question you'll post on the forum. Log files will be
automatically removed on the server after a reasonable amount of time
has elapsed, so you won't need to worry about that. When you post
your request for support, please include a full description of what you
were doing, whatever problem you saw, and roughly what time period you
want us to focus on.
Polar Alignment Tools
PHD2 offers three different polar alignment tools. The three approaches share the same basic
objective: to help you physically align the RA axis of your mount to the
celestial pole. These polar alignment
tools are different from the “two-star” or “three-star” alignment procedures
that are part of many popular go-to mounts.
The mount software routines are generally focused on optimizing go-to
operations, correcting the slewing/pointing operations for a variety of errors
in the mount, including polar alignment error.
They generally don’t involve physical adjustment of the mount’s azimuth
and altitude controls, which is what is necessary for successful imaging and
guiding.
The
three polar alignment tools have different requirements and behaviors,
as summarized in the table below. The accuracy and speed columns
show values in the range of 1-3, where 1 is lowest and 3 is highest.
| Method | Accuracy | Speed | Sky View | Other |
| Static polar alignment | 1 | 3 | Polar region | Requires identification of polar region stars
Minimal slewing |
| Polar drift alignment | 2 | 2 | Polar region | Minimal slewing |
| Traditional drift alignment | 3 | 1 | East or west horizon
Meridian/celestial equator | Most slewing
Axes measured/adjusted separately |
The original polar alignment routine, drift alignment, is
still considered by most to be the “gold standard” for accuracy. Partly, this is because it directly measures
the thing you’re interested in: the amount of drift that will be caused by
mis-alignment of the RA axis on the celestial pole. The drift alignment tool requires use of only
one visible star at a time, and identification of the star is unnecessary. But the procedure can be time-consuming,
especially for beginners, because each mount axis must be adjusted separately
and the telescope will need to slew over a fairly wide area. Also, it works best if you have clear views
of the celestial equator/meridian intersection and an area around 30 degrees
above either the eastern or western horizon (azimuth 90 or 270 degrees). For imagers who are rushing to set up each
night or have a limited view of the sky, these requirements may be
unattractive.
The second alignment option, static polar alignment,
addresses these concerns by taking a different approach. It specifically trades off some accuracy
to optimize the speed of the process. It
requires only a clear view of the northern or southern polar region, and it
facilitates adjustment of both mount axes at the same time. It is therefore a bit more intuitive and quite
likely to be quicker to complete. It
does require visibility and identification of several stars near the pole, but
the tool makes that reasonably easy assuming your sky conditions are good
enough to see the stars.
The third alignment option, polar drift alignment, is probably the
simplest one to perform at the expense of a bit of accuracy and speed.
It
requires a clear view of the northern or southern polar region, and it
facilitates adjustment of both mount axes at the same time. Minimal
user input is needed so it is very simple to use.
The three techniques are described in detail in the following
sections. Imagers should probably
experiment with them and choose the one that best suits their
needs. The importance of alignment
accuracy is often over-emphasized, so users need to keep things in
perspective. Most declination drift can
be well-managed by PHD2 guiding assuming the mount behaves well and doesn’t
have a lot of declination backlash.
However, at some point, the amount of polar alignment error can create
field rotation in the images, something that can’t be corrected. The larger the imaging sensor and the closer
to the pole the target is, the more field rotation can be an issue. You can compute the expected field rotation
using an online calculator such as this one:
http://celestialwonders.com/tools/rotationMaxErrorCalc.html
The calculator can help you decide how much accuracy is
“good enough” for your situation. It’s
also important to remember that any of the procedures can be limited by the
precision of the adjustment mechanisms on the mount.
Lock Positions
PHD2 normally
sets a 'lock position' where the guide star is located at the end of
a calibration. Depending on the details of the calibration
sequence, this may not be exactly where the star was located at the
start of calibration - it could be off by a few pixels. If you
are trying to precisely center your target, you may want to use a
'sticky lock position.' You do this by clicking on your guide
star before calibration, then
setting the 'Sticky Lock Position' under the 'Tools' menu. After
calibration is complete, PHD2 will continue to move the mount until the
star is located at the sticky lock position. So you may see
an additional delay after the calibration while PHD2 repositions the
scope at guide speed. The sticky lock position will continue to
be used even as guiding is stopped and subsequently resumed.
Again, this insures a rigorous positioning of the guide star (and
presumably your image target) at the expense of delays needed for PHD2
to reposition the mount.
If
you need to fine-tune the position of the guide star on the
camera sensor after guiding has begun, you can use the 'Adjust Lock
Position' function under the Tools menu:
You
can nudge the guide star in small increments (at guide speed) or you
can move it by a larger amount by typing in a new lock position
and clicking 'Set'.
Clicking on the up/down/left/right buttons will cause the lock
position to be shifted in the corresponding direction by the amount
shown in 'Step', and the revised lock position will be displayed
If you type in a new lock position, you run the risk of losing
the guide star if the new position falls outside the current
search region. This tool is useful if you need to achieve
precise positioning of either the guide star or the imaging target, for
example with spectroscopy..
Comet Tracking
One way to image a comet is to have PHD2 use the comet as the guide
"star", but this approach may not always work. For example, the head
of the comet may not present a star-like center suitable for
guiding. Or, when using an off-axis guider, the comet may not even be
visible in the guide camera.
PHD2 provides a Comet Tracking tool for use when guiding on the comet
itself is not feasible. The idea is to guide on an ordinary star, but
to gradually shift the lock position to match the comet's motion,
or tracking rate.
There are a three different ways to provide the comet tracking rate to PHD2.
- Some planetarium applications, like Cartes du Ciel, can send the rate directly to PHD2;
- You can enter the tracking rate manually, or,
- You can train the rate in PHD2 by following the comet for a period of time in the imaging camera.
To enter the rates manually, you would select "Arcsec/hr" for units and
"RA/Dec" for axes, then enter the rates from the comet's ephemeris.
If you are getting the rates from the MinorPlanetCenter web site,
you should choose the option for 'Separate RA and Declination
coordinate motions'. PHD2 will automatically adjust the rates to
compute the apparent motions in the sky.
Comet rate training works like this:
First, center the comet in your imaging camera. If your imaging
application has some kind of reticle display, you should use that to
note the precise position of the comet on the imaging sensor. Once
this is ready, select a guide star in PHD2 and start guiding. Next
click "Start" in the Comet Tracking tool to begin training.
Take a continuous series of short exposures in your imaging camera
using your imaging application's Frame and Focus feature. Over time,
the comet will drift away from the starting location. Use PHD2's
"Adjust Lock Position" controls to move the comet back to the starting
location. You may have to experiment a bit to determine which way the
comet moves on the imaging camera sensor in response to the
Up/Down/Left/Right controls in PHD2. You may find it useful to enable
the "Always on top" button in the Adjust Lock Position window so the
controls stay visible on top of your imaging application.
PHD2 will quickly learn the comet tracking rate as you re-center the
comet. Once you are satisfied that PHD2 is tracking the comet, you can
click Stop to end the training. PHD2 will continue shifting the lock
position to track the comet until you disable comet tracking by
toggling the Enable/Disable button.
You can practice the comet training technique using the built-in
camera simulator. Check the "Comet" option in the Camera Settings dialog, and the
simulator will display a comet. Use a bookmark to mark the comet's
starting location, and use the Adjust Lock Position controls to move
the comet back to the bookmark location.
Guiding Assistant
The
Guiding Assistant is an instructional tool to help you measure
current seeing conditions and the general behavior of your mount and
guiding
subsystem. When it's run, it temporarily disables guiding output
and measures the ensuing motion of the guide star. This can help
you
see the high-frequency motions caused by seeing (atmospheric)
conditions. These cannot be corrected by conventional
guiding because they occur at a much higher frequency than you can
typically even measure. Trying to correct for them with conventional
guiding is often called "chasing the seeing" and usually leads to
poor results. Avoiding it is best accomplished by
setting a minimum-move level that will cause PHD2 to ignore most of
this high-frequency behavior. The Guiding Assistant can also show
you other behavior of your system such as overall drift
rates in right ascension and declination as well as peak-to-peak and
maximum-rate-of-change measurements in
right ascension,. While these things can usually be "guided out",
measuring them can be helpful if you want to improve the underlying
performance of the mount - for example, by improving your polar
alignment if the declination drift rate is high. The Guiding
Assistant can also measure the declination backlash in your system if
you select that option in the user interface.
When
you start the Guiding Assistant (GA), its behavior depends on whether
you are already guiding. If guiding is active, the initial screen
will look like this (with different data values of course):
The
topmost field in the form always shows what the GA is doing and what
action you should take, so you should always look there first if you
don't know what's happening. In this case, the measurement
process has been started automatically and you should simply let it run
for at least two minutes. The text field immediately above the
buttons also summarizes what's happening. The three buttons are
enabled or disabled based on the operating state of the GA. In
this case, 'Start' is disabled because the measurement is already
underway.
If you launch the GA when guiding is inactive, the initial form will look different:
In
this case, you'll need to first start guiding in PHD2 - start looping,
select a star, and guide. Once that's done, the 'Start' button in
the GA will be enabled and you can begin measurement.
When
GA measurement is active, guiding commands will be disabled, so the
star
will appear to wander around on the display - this is entirely normal.
As guider images are acquired, statistics are computed and
displayed in real-time in the user interface. After about
two
minutes of data collection, the more volatile measurements like
High-frequency Star Motion and Polar Alignemt Error will usually
stabilize and
you will probably have reasonable overall measurements. If you
want to get a
more accurate measure of your polar alignment error
and any uncorrected periodic error in RA, you'll need to let the
Guiding Assistant run for up to 10 minutes. Also, the computed polar
alignment error is sensitive to the current scope declination. To
get the most accurate measurement, you should point the scope to within
a few degrees of the celestial equator, the same area you should use
for calibration.. When you finally click
the 'Stop'
button, this phase of the measurement process will stop.
If
you've checked the box to 'Measure Declination Backlash" that process
will commence (see below). If not, guiding commands will be
re-enabled and the data collection
process will end. Other computed results will be displayed
in the lower area of the table showing overall drift rates and various
other measurements. All of these values are displayed in
units of both arc-seconds and pixels. The dialog box will look
something like this:
The
contents of the 'Recommendations' group on the right side of the window
reflect the results of the statistical measurements. Assuming
your chosen guide algorithms support a minimum-move property, you have
the option of automatically setting those parameters based on the
results. You can also decide to re-run the measurements or close
the dialog box altogether if you want to proceed with normal guiding
operations.
Measuring Declination Backlash
If
you've checked the box to 'Measure Declination Backlash',
that process will begin as soon as the high-frequency measurements
are completed. In other words, clicking once on the 'Stop' button
halts the high-frequency measurements and begins the measurement of
declination backlash. However, if the initial sampling period was
less than 2 minutes, a dialog box will appear and the backlash test
will continue to sample until the 2-minute period has expired. A
new group of status messages will be
shown immediately above the 'Start' and 'Stop' buttons so you can see
what's being done:
To
do backlash measurement, PHD2 will move the star by large amounts,
first in the north direction, then back to the south. There is
some risk the star will be lost during this process or the star might
already be too close to the north edge of the sensor. You
should choose a guide star that has plenty of room to move north
to get the best accuracy. If the star is lost because it's been
moved outside the search region, you can temporarily increase the size of that region from
the 'Guiding'
tab of the Advanced Settings dialog.
A search region size of 20 pixels should work for most
configurations - just be sure you don't have multiple stars inside
the
search region. The first phase of backlash measurement involves
an initial attempt to clear whatever backlash is present in the north
direction. The Guiding Assistant (GA) will continue with these
clearing commands until it sees a significant and consistent movement
of the
guide star in one direction. Once this is done, the GA will issue
another sequence of commands to continue moving the star north by a
large amount.
This will take at least 16 seconds and may take longer depending
on the configuration - you can watch the status update to see what's
being done. When the north steps are finished, the GA will issue
an identical number of steps in the south direction. If there's
significant backlash in the mount, it may take a long time for the star
to start moving south, but that will usually be handled. Once the
south steps are done, the GA will try to compute an accurate
estimate of the backlash amount, corrected for Declination drift.
This won't be done if the mount never established a consistent
rate of south movement that was at least 90% of the measured rate
moving north That situation usually indicates binding in the
Dec axis or substantial imbalance, in which case a simple estimate
of backlash will be inaccurate and probably irrelevant. You
can always use the 'Show graph' button to see what happened during the
test even if no estimate is produced. When the test is completed,
the GA will try to move the star back close to its
starting position and will re-enable guiding. Again, there is
some risk the star may be lost, but this won't affect the calculations
- you can simply stop and resume guiding as you normally would.
Unlike the first process for measuring high-frequency star
movement, you don't need to click on the 'Stop' button once backlash
measurement has begun. The measurement process will terminate
when all the steps have been completed, and normal guiding will be
resumed. However, you can click on the 'Stop' button if something
has gone wrong - such as a lost-star condition - and then restart when
you're ready. When the backlash tests are finished, you'll see
the results
displayed as before, with the addition of entries for the amount of
declination backlash and the measurement uncertainty (or a status line
that says the test failed):
Depending
on the amount of backlash, you may see a recommendation for setting a
backlash compensation factor - 230 ms in the example shown above.
This type of backlash compensation is different from the feature offered in many mount controllers and is described here: PHD2 backlash compensation If the measured amount is less than 100 ms, no recommendation
will be made because such a small amount probably doesn't warrant any
compensation. If the backlash is very large, over 3 seconds,
you'll see a different recommendation to use uni-directional guiding in
declination. That's because trying to compensate for such large
values probably won't work very well, and the mount will probably not
be able to reverse directions quickly enough to support bi-directional
guiding. Obviously, you can reach your own conclusions based on your
experience with how the mount behaves. Before doing these
measurements, be sure to disable any backlash compensation that's
previously been
enabled in the mount software. If this isn't done, the
measurements and
any subsequent attempts at compensation by PHD2 will be invalid.
If you want to try uni-directional guiding, you can find
instructions here: Uni-directional guiding
You
can look at a graphical display of the backlash measurement results to
get a better understanding of how the mount performed even if the test failed. Just click
on the 'Show Graph' button to see a graph that might look something like
this:
The
green points show the measured declination positions, shown left to
right, beginning with the north moves and ending with the south
(return) moves. The white points show the south-return behavior
for a perfect mount with zero backlash. In this example, there is
only a small amount of backlash as evidenced by the flattened top of
the green
points. However, the flattened top will be more pronounced when
there is significantly more declination backlash in the mount, as in
the following example:
The 'Review Previous' button at the bottom of
the window lets you review the previous three GA results. If
you've run backlash tests at any time, at least one of the three
sessions will include a backlash measurement result. Clicking on
the 'Review' button displays a list of timestamps when a GA was run for
the current profile, so you can just select the date/time you want.
All the grid values and recommendations will be filled with the
results from the selected GA run, including active buttons for applying
the recommendations.
Star-Cross Tool
The star-cross tool can help you test the mount's response to guide commands as described in this trouble-shooting
section. Although the test is easy to perform manually, you may prefer
to use this tool. The star-cross tool will show the following
dialog:
This test presumes you're using the main image camera to expose the image,
so PHD2 doesn't know what image scale is being used for that.
You'll need to be sure the settings are large enough to show a
distinct
pattern on the main camera but not so large that the stars will move
out of the field of view. The default settings should work well
for most set-ups but you can adjust them as needed. The important
thing is to get a clear record of the movement of the stars in the main
camera image and to save that image in a raw, uncompressed format (eg.
FITs or uncompressed TIF). During this test, looping will be
active but no guide star will be selected, and it doesn't matter if
individual stars move out of the guide camera frame. Looping is
activated just so you get some quick visual feedback on whether the
mount
is moving.
Meridian flip calibration Tool
The meridian flip calibration tool (wizard) is used to automatically determine
the correct value for the setting Reverse Dec output after meridian flip.
Running the tool involves two calibrations -- one with the telescope
on the East side of the pier, and one on the West. You will be
instructed to slew (meridian flip) the telescope when needed.
This only needs to be done once for each type of mount you use.
Managing Equipment Profiles
Equipment profiles were introduced in the section on Basic Use
where they are used as part of the 'Connect Equipment' dialog. If
you want to manage multiple profiles, you will probably want to use the
'Manage Profiles' button in the 'Connect Equipment' dialog. Using
the menu items there, you can create a new profile
or edit/rename/delete an existing one. Each profile holds
all the settings that were active at the time the profile was last
used. If you create a new profile, you can import these settings
from either the PHD2
generic defaults or from an existing profile. You can also use the
'Wizard' option to have PHD2 establish settings that are specific to
your equipment configuration. To
edit the settings in an existing profile, you first select it in the
equipment profile drop-down list, then click on 'Settings' under the
'Manage Profiles' pull-down. This will take you to the Advanced Settings
dialog, where you can make whatever changes you want. Remember
that profiles are automatically updated anytime settings are changed
during a PHD2 session. Finally, you can import and export
profiles for purposes of debugging, backup, or exchange between computers.
Aux-Mount Connection using "Ask for coordinates"
If
you can't connect to your mount using either ASCOM or INDI drivers, you
still have a better-than-nothing alternative by using the "Ask for
coordinates" aux-mount connection. With this option, you'll be asked
to enter or confirm the scope position each time guiding is going
to begin::
If
you enter your scope's current declination and side-of-pier values,
PHD2 will automatically adjust the calibration to match that
pointing position. You don't need to be precise, a
Declination value that's within a few degrees will work. This
means you won't need to recalibrate as you slew to different targets
so long as you update these values each time. For
example, you can do a calibration near Declination=0 then enter
new position values when you've slewed to a high declination imaging
target.
This is likely to produce a better result than trying to
calibrate at a near-pole position. This dialog will not be
displayed if the start of guiding is the result of a dither operation
or a server command from an imaging application. In order for the
calibration adjustment to work correctly, your previous calibration must have been completed with correct positioning data available.
If you're using this option with the Drift Alignment tool, the dialog will look a bit different:
If
you enter the additional information for Right Ascension, latitude, and
longitude, the Drift Alignment tool can more accurately adjust its
magenta target circle. Otherwise, the circle will show only an
upper-bound estimate of the pointing error during the 'adjustment'
phases.
You
can connect or disconnect the "Ask for
coordinates" aux-mount without affecting the camera or mount
connections. So you might decide to use the option for drift
alignment or for an initial slew to your imaging target, then
disconnect from it in order to avoid
the repetitive dialog displays. Regardless of how you choose to
use it, you're
responsible for having the correct values in place, and you should
remember that significantly wrong values can result in poor guiding
results.
Advanced Settings for the Simulators
The device simulators were introduced in the Basic Use
section as useful tools for experimenting with PHD2
and becoming
familiar with its features. Remember that you must choose
'Simulator' as the camera type and 'On-camera' as the mount type in
order to get the benefits of simulation. As you become more
interested in the details of the simulation, you can use the 'Camera
Settings' button on the main display to adjust the simulation
parameters:
You can adjust simulated mount behaviors for declination backlash, drift
due to polar mis-alignment, and periodic error. You can also
adjust the 'seeing' level, which will create fairly realistic guide
star deflections that look like seeing effects. If you adjust
these parameters one-by-one, you'll see how they affect star
deflections and how the different guide algorithms react to those
movements. Of course, you're dealing with a "nearly perfect" mount in
these scenarios (except for backlash), so the simulation can't be entirely realistic.
Multiple Program Executions
In
some situations, you may want to run multiple instances of PHD2 at the
same time. To start the second instance of PHD2, you need to
supply a command-line parameter of -i 2; the third instance would be
started with -i 3, etc. You can accomplish this in Windows by
running PHD2 from a command line using the Windows cmd.exe utility.
Or you can create a Windows desktop shortcut by doing the
following:
Right-click on your desktop
Select: New/Shortcut
Enter the following string to identify the location of the program: "C:\Program File (x86)\PHDBuiding2\PHD2.exe" -i2
Click Next
Enter a name for the shortcut, e.g. PHD2 #2
Click Finish
Note the quotes around the name in the 3rd line are required by Windows because there are blanks embedded in the directory name.
Keyboard Shortcuts
Keyboard
shortcuts are available for many of the more commonly used tools and
functions in PHD2. These are enumerated in the Keyboard Shortcuts section.
Software Update
One of the most common responses to a request for support in the PHD2
Forum is: please upgrade to the latest version and see if the problem
still exists. If you are seeing an issue in an older version of PHD2
it is quite likely that you are not the first person to encounter it,
and that it has already been reported and fixed in a newer version of
PHD2. For this reason, the developers of PHD2 feel that it is
important to be running the most up-to-date version of the program.
Upgrading a program that you rely on for unattended imaging in our
limited available clear sky time can sometimes be perceived as a risky
proposition. The developers of PHD2 recognize this sentiment--we are
imagers too! There is a necessary trade-off between maintaining a
stable software installation and staying current with the latest
bug fixes and other improvements.
PHD2 achieves a balance between these two opposing needs by
publishing two series of software releases. The development releases
contain the latest ongoing bug fixes and feature improvements and are
tested by the developers--usually during actual imaging time--before
being released. Users who choose to run the development releases will
get the latest bug fixes and newest features. Development releases
have names like "2.6.3dev6" indicating, for example, the 6th
development release after the 2.6.3 major release.
Periodically, after a development release has received more test
time, it will be published as a major release. For example, 2.6.3dev6
could be published as major release 2.6.4.
Checking for updates
PHD2 has an option to automatically check for software updates. We
recommend enabling this option to help keep your version of
PHD2 up to date. When the automatic check option is enabled, PHD2 will
quietly check for updates in the background when PHD2 starts. If new
updates are available, PHD2 will give you the option to install the
new version. Enabling the automatic check for updates will not
interfere with the ordinary operation of PHD2, including automated
operation. It is also safe to leave the option enabled if you are
imaging in the field without internet connectivity. If PHD2 cannot
check for updates, it will wait until the next time it is started before
trying to check again.
Regardless of whether you allow PHD2 to automatically check for
updates at startup, you can always manually check for updates by
clicking "Check for updates" from the Help menu.