Tools and Utilities

Manual Guide
Auto-Select Star
Calibration Data
PHD2 Server
Drift Alignment
Lock Positions
Comet Tracking
Equipment Profiles
Simulator Parameters

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. 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 calibration problems, listen to (rather than watch) your mount to determine if the mount 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 it. Other options include watching the motors themselves or attaching a laser pointer to your scope and aiming it at something fairly far away (to amplify your motions).  If you have an adaptive optics device attached, you'll see separate move buttons for both the AO and the secondary mount.  

Dithering is used primarily with image capture or automation applications, usually 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 near another star and not too close to the edge of the frame.  The selected star may appear overly dim on the screen, but this is usually not a problem.  You can use the Star Profile tool to examine the properties of the selected star - it should be non-saturated with a sharp profile, the same properties you should look for when choosing a guide star manually.  The auto-select process is not infallible, so you may need to select a star yourself if you don't like the automated result.  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.

Manual Control of Calibration Data

Calibration data is 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 '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.

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.

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, click on 'Drift Align' under the 'Tools' menu.  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 proceed 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:
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 horizon.  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, especially in declination.

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.  If you can't do that for some reason, the following features will be impaired:
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. (https://sites.google.com/site/openphdguiding/phd2-drift-alignment)

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.






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 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.

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.

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.