This section describes the second tab of the Guider Settings dialog, which is activated from the Settings button on the Guide Tab. Please note that some fields are disabled while the guider is running. Those that do not grey out are still active and can be changed while the guider is running. Changes take effect immediately upon clicking Apply or a "spin" up/down button.
The Guiding controls set limits for track mode operations. The Minimum Move X and Minimum Move Y sets the smallest motion the autoguider will make. When the duration of the pulse to be sent to the telescope is less than the Minimum Move value, it is not sent. Some users set this to about 1/3 of the seeing disk size to prevent unnecessary corrections, oscillations, and reduce stiction cycles. The Maximum Move X and Maximum Move Y can be used to limit the maximum amount of motion permitted during guiding. Lowering this value can prevent the guider from tracking out a momentary large error, such as might occur if a large wind gust affects the mount.
A non-zero value in the Delay After Correction field causes a time delay after each guider output command. This allows time for the telescope to settle (or, in the case of serial output command mode, for the guider activation itself to complete) prior to taking the next guider image. A small delay is also recommended when using Losmandy mounts.
The Move Commands settings control the behavior of the Move dialog (accessed using the Guide Tab’s Move button). Maximum Slew X and Maximum Slew Y limit the maximum slew that will be performed using this command. These limits can be set to prevent large, accidental slews. The Delay After Command control allows you to program in a delay after each move command. It should be used in the same situations for which Delay After Correction is recommended.
The Guider Motor Control affects how commands are sent to the mount, as follows.
Some telescope mounts can accept guider move commands for both axes simultaneously, but some cannot. By default, MaxIm DL sends correction commands to each axis sequentially. If your mount is capable of guiding in both axes at the same time, you can turn on Enable Simultaneous RA and Dec Correction. Doing so will speed up the guider cycle time slightly; however, if your mount cannot accept simultaneous commands it may act very erratically and fail to guide. If in doubt leave this setting turned off. Also, this setting is ignored when Control Via is set to Telescope because the ASCOM telescope interface does not permit this mode of operation.
Following a pier flip, most mounts will reverse the direction of autoguider commands in the Y direction. This is actually the result of the camera rotating 180 degrees (reversing both X and Y), and the direction of mechanical declination reversing (reverting Y back to normal). By setting On Pier Flip Reverse X, the autoguider calibration will automatically be preserved after a pier flip. This setting works for most telescopes, as long as X is wired to RA. If X is wired to Declination, then select Reverse Y. Some mounts behave differently due to intelligence in their controller, and preserve the sense of the declination axis. For these mounts select Reverse X and Y. A Do Not Change option is also provided, which will do nothing when a pier flip occurs. Some mounts do not report "side of pier", in which case MaxIm DL has to "guess" what side they are on. Some of these mounts, including the Paramount ME, can be difficult to predict. The Adaptive mode watches the guide star, and if it starts to drift away it automatically reverses the guide corrections. The Adaptive mode will often take longer to settle after a pier flip or slew, but guiding should not fail completely even if the telescope does something unexpected. Please note that these settings require Auto Pier Flip on the Guide tab to be turned on in order to have any effect. Also please note that you may need to recalibrate the guider after changing this setting.
Offset Tracking is an advanced feature that allows you to specify a series of positions for the guider to track to. This can be used to track solar system objects such as asteroids and comets, or to compensate for flexure in your system.
Click the Select File button under Offset Tracking to select the offset file. Locate your file and open it, then click OK. The next time you start a tracking session the offset mode will be started.
The format of the offset file is flexible. Times and positions can be specified either in relative or absolute coordinates.
The format for relative coordinates is as follows:
ss +/-x.x +/-y.y
ss - Time delay from last movement
+/- - Direction of movement; i.e. either + or - (required)
x.x - Amount of movement in X direction (in pixels)
y.y - Amount of movement in Y direction (in pixels)
An example of relative offsets is:
15 +0.5 -0.5
15 +0.5 -0.5
15 +1.0 -1.0
Fifteen seconds after guiding starts, the guide point would be moved half a pixel to the right, and half a pixel up. The same thing would happen 30 seconds into the exposure, and so on. Avoid moving the guide point more than a small amount in each step. If the guide star's surrounding trackbox reaches beyond the edge of the guide image frame, offset tracking will be disabled.
The format for absolute coordinates is as follows:
hh:mm:ss x.x y.y
hh:mm:ss UT time in hours, minutes and seconds
x.x New X position in absolute coordinates
y.y New Y position in absolute coordinates
An example of absolute offsets is:
22:05:15 255.0 255.0
22:05:45 255.5 255.0
22:06:15 255.5 253.5
In this example, at UT 22:05:45, the guide point will be moved to coordinates X=255.5, Y=255.0. You must be careful to move the guide point slowly or the lock could be lost.
(For both relative and absolute formats, avoid inserting spaces next to the colons or decimal points, or after the signs. Otherwise the values will be misinterpreted.)
To disable Offset Tracking, click the Clear button.
Changes to most controls on this dialog do not take effect until you either close the dialog or click the Apply button. When a control has been altered, the Apply button enables automatically to remind you that it has not yet taken effect.
The Defaults button resets all controls except the Offset Tracking group to their "factory defaults".
Tip: the scripting interface also supports offsets. See http://www.diffractionlimited.com/products/maxim_extras.htm for an offset tracking utility that works through the scripting interface.