Contents - Index

Focusing

Here you set the various parameters for focusing during your session. There are many issues surrounding focusing and reading the Focusing Techniques topic is recommended to aid in your Focusing choices. CCDAutoPilot supports three automated focusing systems: FocusMax which works with both CCDSoft and Maxim, CCDSoft's @focus2, Maxim's internal focus routine and PlaneWave AutoFocus (if enabled). Which one to use is a matter of personal preference and which works best for your system.  The focusing page changes slightly, depending on the focusing server choice.  This topic will discuss FocusMax in detail and discuss the changes for the other programs.

For all focusing servers, when an equatorial-mounted telescope is pointed east of the meridian, any focusing activity scheduled to occur within 4 focusing time estimates of the meridian crossing will be deferred until the telescope has crossed the meridian and the mount has flipped. The focusing time estimate used is as defined on the Time Estimates tab. This deferral does not take place with fork-mounted telescope.  This focus deferral only occurs when Meridian Flip is selected.


FocusMax



Before proceeding, insure that FocusMax is set up properly for your system.  Consult FocusMax documentation for specifics.  Once all the software is linked to CCDAutoPilot, you can use the Focus Now button to verify operation. Focus Now uses the settings on this page to launch a mini-session that only focuses and does whatever other telescope moving might be required. Its actions are recorded as a normal log and displayed in the Session window.

Focus Methods

When FocusMax is connected, there are a number of active methods of focusing available.  Active methods do not rely on predicting the focus position but actually focus the system at appropriate times.  As such, this would be expected to give you the most optimal focus at any point in time.  The trade-off here is the time to do the focusing.  Depending on the method chosen, active focusing can add from 30 to 300 seconds or more, depending on the method used, camera download time etc.
  • None: No focusing is used. This setting might be used if it is desired to use only filter offsets.
  • Brightest star in FOV: FocusMax will choose the brightest object in the field of view. This is fine if there are no bright extended objects such as galaxies in the field but if there are, FocusMax will attempt to focus on that and will most likely be unsuccessful. 
  • Focus at X, Y: One way to avoid the above problem is to select a specific x,y coordinate for a target star. Take an unbinned image and note the coordinates of the brightest star. Enter those coordinates in the X and Y boxes. FocusMax will use that coordinate with a 100 x 100 pixel box around it to focus. 
  • Sky Star: With this technique and TheSky, CCDAutoPilot will plate solve the current location, slew the scope to a nearby star, focus there using FocusMax, @Focus2 or Maxim's focus routine, and slew back to the original location. If guiding was in process, it will be stopped for focusing and restarted automatically once the telescope has returned to the target coordinates. This technique guarantees a suitable star for focusing and uses the very powerful data query technology of TheSky to select stars of an appropriate magnitude to be used for focusing. SkyStar has some additional options: Center Focus Star within: When checked, a precision slew to the focus star will be made, insuring the focus star is in the center of the FOV and allows you to specify how close the focus star will be to the center of the imager's FOV.  Magnitude Range:  4 magnitude ranges are provided for the focus star - 4 to 7, 5 to 8, 6 to 9 and 7 to 10.  Select the range that is appropriate for your system.  Minimum focus star altitude: Regardless of where the telescope is pointing, focusing will always use a star above this minimum altitude.  As a minimum, you must have the Guide Star Catalog (GSC) selected as one of the Stellar Core databases in TheSky. The selected stars' magnitude range and catalog can be customized. See Advanced Customization.
  • Focus Program Picks Star: This is similar to Sky Star but it is all done within FocusMax using AcquireStar and requires the full version of PinPoint. (FocusMax V5 supports plate solving via TheSky).  Unlike SkyStar, whatever filter you use to focus on will be the same filter used for plate solving.  CCDAutoPilot will use precision slew to correct any returning slew errors from the focus program. When using FocusMax V5, a Multi-star checkbox is enabled. When checked, CCDAutoPilot will initiate FocusMax's new Multi-star focusing technique. Since this depends on sufficient focus stars in the FOV, it is recommended that "Run AcquireStar on failure" in FocusMax Preferences, AutoFocus if the Multi-star is checked in CCDAutoPilot. See FocusMax help file for details.
  • Refocus every xx minutes: When checked and depending on the numeric entry, the chosen focus method will be executed xx minutes after the start of the first target's imaging session. The next exposure that comes along that is xx or more minutes after the last focus will be executed. In other words, the time for an interval focus is determined before an exposure starts.  If xx minutes has elapsed since the last focus, a focus run will be performed; if it hasn't elapsed, the checking process will repeat before the next exposure starts.  You should set up a brief series of exposures to insure FocusMax can focus satisfactorily with all of the planned filters in place, adjusting the focus exposure to be appropriate to a given filter as described below. Make any adjustments to the FocusMax settings required.
  • Filter for Focusing: If your filters are sufficiently parfocal, i.e. they all focus at the same point, you may choose to use one specific filter for focusing.  That way you can avoid having to deal with different focus exposures for different filters. If your filters are not parfocal, you should determine and use filter offsets.
  • Ignore Failed Focus Stars: When CCDAutoPilot chooses stars for focusing with SkyStar, occasional near doubles or other objects may prevent successful focusing. (Stars in the WDS catalog are automatically excluded.) When this box is checked, CCDAutoPilot learns which stars fail to successfully focus and builds a database that is stored in the system profile. Therefore on subsequent attempts to focus at a star near the same target, the problem star will be skipped on subsequent focus attempts and new stars will be used. Unchecking this box will clear the saved database so if you wish to operate without this feature and still keep the database, save the system profile to a new name before unchecking the box. The newly named system profile will still have the learned database and the current one will not. The excluded stars are noted in the Preview pane on the Run page. At the conclusion of the session, any newly discovered focus failure stars are added to the database and reported in the log. Note this is a SkyStar feature only. The Clear Database button deletes all the failed focus stars from the database and can not be undone. If there is any doubt, make a backup of your system profile before hitting tthis button.
  • Post Focus Offset: This setting can be used to minimize the effects of OTA field curvature.  The intent is to "split the difference" between perfect focus at the center and focusing at the edge of the field of view.  For OTA's without a field flattener and/or a large imaging chip, there can be a significant difference in the focus position between center and edge.  First, determine the focus at the center of your OTA and then determine it at some point away from the center.  A good starting point is 60% of the way to the corner.  You can use the Focus Now button to determine these values.  Average a number of focus runs at each location.  Calculate the offset and enter it in the Post Focus Offset.  For best results, the Center Focus Star option and SkyStar focusing should be used.  After achieving focus, the post focus offset will be added or subtracted to the focus results, according to the sign of the entry.
  • Focus Timeout: Occasionally a focus routine can end up never getting to a focus position that meets its requirements.  By setting this timeout, your session will continue after the specified timeout, aborting the focus activity in progress and resetting the focuser position to where it was before the focus routine started.
  • Backlash Compensation: When a non-zero value, positive or negative, is entered here and an offset is required for a given filter, the focuser is moved past the desired filter offset by the amount of backlash compensation entered and then it is moved again to remove the offset. Normal use case is to always approach the desired focus offset from the same direction, thereby minimiizing backlash. Setting this value to 0 disables backlash compensation.
    Example. Assue a telescope with a draw tube focuers is being uses, such that increasing counts moves the camera further away from the telescope. Any backlash will become more of an issue as the telescope is pointed more toward the zenith, leading to a possible focuser positional error due to backlash. If a positive value is entered for backlash compensation, and the desired position is 3000 for a given filter, the focuser will move first to 3050 and then back 50 to 3000. The advantage here is the position is always arrived at from the same direction, i.e. against gravity in this example, increasing offset repeatability. Backlash compensation is used only during series filter changes and not during focusing. Focusing programs like FocusMax, have a backlash compensation facility included. 

    Temperature Dependent Refocus
    By characterizing your imaging system's performance, it is possible to refocus only when necessary.  Knowing how much temperature impacts your focus, you may elect to refocus every time the temperature change is such that your focus moves out of the Critical Focus zone.  Thus, having a source of temperature measurement and knowing how much of a change will adversely impact your focus, you can check Focus on Temp Change of, enter a suitable change amount, select the Temperature Source, and refocus as needed.  Depending on what control programs are connected to CCDAutoPilot, the available choices will be selectable as temperature sources.  Make sure you choose one if you are using this option.

    Temperature Compensation
    If Use Temp. Slope of is checked and your focuser supports temperature compensation, it will be enabled. Temperature compensation will be disabled automatically during the main exposure. At the conclusion of the main exposure, temperature compensation will be re-enabled and a 5 second delay will be initiated to allow time for temperature compensation.  To use temperature compensation, the user must provide a Compensation Slope that appropriately characterizes the system.  This value should be counts/temperature needed to maintain focus.  When Temperature Source is changed, the reported temperature will be shown in the status bar.  If "n/a" is shown, the source selected does not report temperature and temperature compensation cannot be used.  There are many ways to determine the compensation slope.  The basic process is to measure the focus point at different temperatures and calculate the slope.  An imaging session with 10 minute exposures and a focus before every exposure during a period of temperature change is a good way to get the raw data.  A least squares fit then gives a good slope.  The compensation slope should be in units of focuser count per unit temperature.  Be sure the temperature reported, °C, °F or counts used for the measurement is the same as that reported as Temperature Source.  The focus starting point will be determined at the beginning of a session and the starting temperature noted.  At each subsequent focus adjustment, the starting point and temperature will be redefined.  Between exposures, the focus point will be adjusted, based on the current temperature and the user-supplied Compensation Slope. Note: If focuser temperature compensation is enabled in either your focuser or focus control program, it must be disabled when CCDAutoPilot is linked.


    TheSkyX Camera Add On and CCDSoft @Focus2 Differences

  • @Focus 2 has a limited choices of Focus Methods as shown above and the Magnitude Range is not needed since it uses its own database query to find focus stars. However, the stars' magnitude range and catalog can be customized. See Advanced Customization.

    Note: @Focus2 will optionally use an autodark if an autodark is specified on the Plate Solving tab. If the camera does not have a shutter, the autodark selection should not be checked.





    Maxim




     Maxim's internal focus routine fewer Focus Methods, as shown above.


    PlaneWave AutoFocus

    The only focusing option shown is PlaneWave AutoFocus. During an automated session, logging is suspended during PW AutoFocus but will resume once the AutoFocus routine completes or is aborted. Consult PlaneWave documentation for details. See also Filter Factors.


    @Focus3


    @Focus3 modes as shown above. When TheSkyX build 11117 or later is connected and TheSkyX connects to a focuser, these focus modes are availble.
  • None:  No focusing mode is selected so focusing will not happen.
  • Automatic Sub-frame: @Focus3 will determine the star to focus on and automatically sub-frame around it for optimal focusing. This is the recommended mode for most cases. Focusing will proceed automatically and return control to CCDAutoPilot when complete.
  • Manual Sub-frame: Whatever sub-frame is manually specified in TheSkyX  will be used. Please see TheASkyX user guide for setting this feature.
  • Number of Samples: Sets the number of samples for each focus measurement during an @Focus3 session. See TheSkyX User Guide for more details.