Tools and Utilities

Tools and Utilities

Manual Guide
Auto-Select Star
Calibration Details
PHD2 Server
Dithering Operations
Logging and Debug Output
Drift Alignment
Lock Positions
Comet Tracking
Guiding Assistant
Equipment Profiles
Ask for Connections Aux Mount
Simulator Parameters
Multiple Program Instances
Keyboard Shortcuts

Manual Guide

If you are connecting to a new mount and 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-sze' set in the Advanced Options 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 through 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

Clicking on 'Auto-select Star' under the 'Tools' menu, or using the keyboard shortcut of <Alt>S, tells PHD2 to scan the current guide image and identify a star suitable for guiding.  PHD2 will try to select a star of sufficient brightness that is not saturated, not near another star, and not 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 usually 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.  If you want to use Auto-Select, you should definitely use either a bad-pixel map or dark library to reduce the likelihood of PHD2 mistakenly choosing a hot pixel.

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 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.  Stark Labs' Nebulosity program was the first to do this, but other applications have subsequently been produced.  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 server interface has been reworked substantially in PHD2, and it's now possible for an application to control most aspects of PHD2's guiding operations.  Documentation for the server API is available on the PHD2 Wiki.


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 almost purely 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 also removed in post-processing, but that becomes tedious if there are lots of them.  It's also possible that 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 for those reasons. 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.. Then, 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. You want to use pseudo-random dither amounts like this to be sure that dithering doesn't follow a consistent 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 Brain 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.

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' ('Global tab of the Brain 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 guiding log is similar to the one produced by PHD, but with extended information. The guide log is intentionally formatted to allow easy interpretation by either a human reader or an external application.  For example, the very capable 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 that a comma should be used 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 application data files.  In Windows7, for example, the files will be stored in a 'PHD2' sub-folder in the "AppData\Local" location.  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.

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.

Drift Align

Drift alignment is a well-known technique for achieving polar alignment and is considered by many to be the "gold standard".  The Drift Alignment tool is a wizard-like sequence of dialogs that can help you work through the drift alignment process and get quantifiable results.  Once you've calibrated your guider and have started guiding, click on 'Drift Align' under the 'Tools' menu.  The Drift Alignment tool will disable and re-enable declination guiding as necessary, so don't worry about that.  It will also keep RA guiding active so uncorrected periodic error in the mount doesn't interfere with the measurements.  The first Drift Align dialog will appear to help you adjust the azimuth on your mount.  If you are using an ASCOM mount, you'll have the option of slewing to an area near the celestial equator and the celestial meridian.  If you're not using an ASCOM mount, you'll need to slew to that location manually.  Once the scope is positioned and you have a suitable star in the field of view, click on the 'Drift' button to begin collecting data.  You'll see the graph window with a display of star deflections and corrections and, more importantly, two trendlines. When the mount is precisely polar aligned in azimuth, the Declination trend line will be perfectly horizontal.  Let the exposures continue until the declination trendline has stabilized and is no longer jumping around with each new exposure.  At the bottom of the graph window, you'll see a measurement for the polar alignment error in azimuth. And, in the image window, you will see a magenta circle around the guide star. The circle indicates an upper limit on how far the guide star needs to move when azimuth is adjusted. (Initially, the circle may be too large to be visible on the screen, so you may not see it until your alignment gets closer.)

Now click on the 'Adjust' button to halt guiding, then make a  mechanical adjustment in azimuth. Watch the guide star as you make the adjustment, moving the guide star towards the magenta circle, but not beyond it. Once done, click on the 'drift' button again to repeat the measurement. If your adjustment was in the right direction and did not over-shoot, the Declination trendline will be closer to horizontal.  Continue iterating in this way until you are satisfied with your azimuth accuracy.  You can use the 'notes' field to record which way the drift line moves depending on how you make the adjustment.  For example, you might note that a counter-clockwise turn of the mount azimuth knob moves the drift line "up."  Since these notes are retained across PHD2 sessions, subsequent drift alignments will probably go more quickly.

Until you are experienced with drift aligning your particular mount, the 'adjustment' part of the process can be a bit tedious.  At first, you'll have to determine how to adjust a knob on the mount to achieve the desired effect: "how much" and "what direction."  To help with this, the PHD2 drift align tool supports "bookmarks".  These are a handy way to record the positions of the guide star before and after you've made an adjustment.  Bookmarks are accessed using the Bookmarks menu, or keyboard shortcuts, as follows:
  • b : toggle/show bookmarks 
  • Shift-b : set a bookark at the current guide star position (the "lock position")
  • Ctrl-b : clear all bookmarks 
  • Ctrl-click somewhere on the image: set a bookmark at that position, or remove the bookmark that's already there
By setting a bookmark before you make a mount adjustment, you can get a clear view of how the adjustment has moved the star on the guide frame.

Next, click on the 'Altitude' button.  Then slew the scope to a position near the celestial equator and 25-30 degrees above the east or west horizon.  If you have obstructions in both directions and can't slew this low, don't worry about it - just get as close as you can.  Using higher elevations on the east or west horizon will still work, but it may take a bit longer to converge on your final polar alignment.  Click on the 'drift' button to begin collecting data for the altitude part of the alignment process.  As before, you will iterate between making adjustments and measuring your alignment until you are satisfied with the result, keeping notes as you go about how mount adjustments affect the behavior of the declination drift line.  If you make substantial adjustments in altitude, you'll need to go back to the 'azimuth' measurement and repeat that procedure.  If you work through these procedures systematically, you'll converge on a good polar alignment with a known degree of accuracy.  A good polar alignment will help your guiding performance and will avoid field rotation in your images..

The drift alignment tool is easiest to use when you are using an ASCOM connection to your mount (including an 'Aux' connection).  Even if you subsequently want to use ST-4 style guiding, you should use the ASCOM connection for drift alignment to make things easier.  If you can't do that for some reason, the following features will be impaired:
  • Scope position data and slewing functions will not be available - you'll have to slew the scope yourself.  Keep in mind, the target altitude/azimuth positions are only approximate - you don't need to be particularly concerned about accuracy - just get reasonably close with a good guide star available in the field of view.
  • The magenta circle that identifies the target for moving the star will be inaccurate and will be displayed as a dashed line.  This dashed circle will identify only an upper bound to the adjustment, so you will probably want to make smaller adjustments to avoid over-shooting.
A very complete step-by-step tutorial for drift alignment is available on the Openphdguiding web site, and first-time users are strongly encouraged to study it. (

Lock Positions

PHD2 normally sets a 'lock position' where the guide star is located at the end of 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.

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 rate manually, you would select "Arcsec/hr" for units and "RA/Dec" for axes, then enter the rates from the comet's ephemeris.

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 Cam 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 the Guiding Assistant is first started, you'll see a dialog box like this:

The upper message area in the Guiding Assistant dialog box displays usage instructions, much like a wizard interface.  In order for the Guiding Assistant to start measurement, you first need to start guiding in the usual way.  This identifies the target star in the frame and enables (but does not start) the underlying data collection mechanism.  You then click 'Start' in the Guiding Assistant to begin the measurement process.  Once you do this, 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. Of particular interest are the table entries in the "High-frequency Star Motion" section which show ongoing results of the averaging process.  After about one minute of data collection, these numbers will usually stabilize and you'll have a reasonable measurement of the high-frequency star movement caused by seeing conditions.  You'll also have a rough measure of your polar alignment error although the accuracy will improve if you let the sampling run for longer periods of time.  If you want to get an 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. 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.  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, regardless of how far the star has actually moved,  the backlash amount will be computed.  However, if the star hasn’t moved at all in the south direction, the computed backlash amount will be too small.  At that point, you can know your declination backlash exceeds 8 seconds, which is a very large amount. The Guiding Assistant will then try to move the star back 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 in units of both pixels and time (ms):

Depending on the amount of backlash, you may see a recommendation for setting a backlash compensation factor - 100 ms in the example shown above.  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.  Just click on the 'Show Graph' button to see a graph that might look something like this:

The red points show the measured declination positions, shown left to right, beginning with the north moves and ending with the south (return) moves.  The blue points show the south-return behavior for a perfect mount with zero backlash.  In this example, there is only a modest amount of backlash as evidenced by the flattened top of the red points. However, the flattened top will be much more pronounced when there is significantly more declination backlash in the mount, as in the following example:

Declination Backlash Compensation
Starting with the 2.5 release, PHD2 supports a backlash compensation mechanism that may help to improve  mount performance when there is a moderate amount of declination backlash.  It is different from the backlash compensation that's supported in some mount firmware because the PHD2 implementation is adaptive.  The greatest risk with backlash compensation is that it will be too large and will drive the mount into unstable oscillations in declination.  PHD2 will watch for this behavior and rapidly and automatically adjust the compensation downward until the oscillation disappears.  Obviously, backlash compensation is applied only when the direction of declination guiding is reversed.  When you first set a backlash compensation parameter with the Guiding Assistant (recommendations section), you should give PHD2 some time to adjust it.  Let normal guiding proceed and watch for over-shoots in declination.  You can see these pretty easily by watching the guiding graph with the option checked to show guiding corrections.  If you see some initial oscillation and instability in declination, let guiding run for awhile to see if PHD2 can stabilize the behavior.  

The setting for backlash compensation is shown in the 'Algorithms' tab of the Advanced Settings dialog. The value shown there may be smaller than what was computed by the Guiding Assistant if PHD2 had to adjust it downward.  You can modify this parameter directly if you want to experiment with it or you can disable backlash compensation altogether using the adjacent checkbox.  Once you've measured the backlash a few times with the GA and see a fairly consistent pattern of results, there's  probably no need to measure it every time you run the GA.  Just uncheck the 'Measure Declination Backlash' option until you want to measure it again.

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 activiated just so you get some quick visual feedback on whether the mount is moving.

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 'Brain' dialog, where you can make whatever changes you want.  Remember than 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 even exchange with other PHD2 users.

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 you to experiment with PHD2 and become famliar 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 'Cam Dialog' 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.

News & Resources

February 12, 2017 - PHD2 v2.6.3 Released

October 28, 2016 - PHD2 Best Practices

June 12, 2016 - PHD2_Broker package available

December 29, 2015 - Tutorial: Analyzing PHD2 Guiding Results

December 20, 2015 - Tutorial: Off-axis guiding on comets with PHD2