| GUIDE CHOICES |
|
|
| Guiding Algorithms: |
|---|
| Stop Guiding: |
Suspend guiding, i.e., stop sending
instructions to the telescope to make corrections. |
| Start [] Guiding (balanced reticles): |
Begin guiding using an algorithm which seeks to balance the flux in
Left/Right and Top/Bottom reticles respectively. This algorithm will center
an object on the reticle and try to hold it there. The algorithm works best
for symmetrical targets such as stars. |
| Start [] Guiding (fixed ratio reticles): |
Begin guiding using an algorithm which seeks to maintain the flux ratios
measured in the Left/Right and Top/Bottom reticles respectively when guiding
is initiated. This algorithm tries to hold an object on the reticles at
the position at the time guiding is started. The algorithm allows one to
guide on asymmetrical or off-center targets. |
| Start Guiding with profile fitting: |
Begin guiding using the "profile guiding" algorithm. This is them most sophisticated
of the guiding algorithms. It measures the flux across rows and across columns in
the Left/Right and Up/Down reticles respectively, fitting a parabola to each measurement
to determine the object's centroid and its distance from the center of the reticles.
Using this information, the algorithm computes the appropriate size and direction of
the telescope move needed to make any necessary correctons. Profile fitting works best
on symmetrical targets. Note that when guiding in a slit with only the wings of the object
visible, this algorithm interpolates across the slit to fit the parabola. |
| Reticle and Star Motions: |
|---|
| Center reticle on star: |
With the at least some of the object already in the reticle, this option
centers the reticle on the object. |
| Move star to guide reticle: |
After selecting this option a box appears instructing the user to left-click on the
target object in the image display. The telescope is then automatically moved to
bring the object onto the reticle. This option requires that the correct plate scale
entered under Guide Parameters. |
| Move star to selected location: |
After selecting this option a box appears instructing the user to left-click on the
target object in the image display, then to click again on a location in the display.
The telescope is then automatically moved to place the selected target at the new
location. This option requires that the correct plate scale
entered under Guide Parameters. |
| Focusing tools: |
|---|
| Check star focus: |
A number represents the sum of the instantaneous derivatives along the light-intensity curve.
You can track this value for optimal focus. |
| Check slit focus: |
|
| GUIDE PARAMETERS |
|
|
`
| Sigma Threshold: |
Sets the comparative flux in the guide reticles and sky box, in standard deviations,
below which the guider assumes no object to be present on the reticle and suspends
guiding. This feature is useful if, for example, passing clouds cause the guiding object to
become very faint or disappear. |
| Repeat Count: |
Sets the number of consecutive times the guide object must meet the criteria for a
telescope correction, before that correction is made. This feature helps to prevent
guiding on noise such as rapid, random deviations due to seeing. A repeat count of 2
seems to be a good default, but the best value for this
parameter may vary with sky conditions. |
| Maximum Ratio: |
For balanced reticle guiding, this sets the maximum allowable deviation
from the "Minimum Ratio" (usually 0.50) before the guider will consider that a correction is
needed. A maximum ratio only slightly larger than the minimum, e.g., 0.51, might cause
overguiding. A maximum ratio of 0.55 seems to be a good default, but the best value for this
parameter may vary with sky conditions.
This parameter is ignored when using the
profile fitting guide algorithm. |
| Minimum Ratio: |
This value is generally set to 0.50. It is ignored when using the
profile fitting guide algorithm. |
| E/W & N/S sign: |
These values are analogous to the "guide matrix" of the old guiders. E/W and N/S pertain
to directions on the sky; Row and Column pertain to directions on the display.
Signs should set themselves correctly, provided the version of the guider appropriate to the
telescope, focus, and instrument has been chosen at startup
Where a TUB diagonal mirror is part of the system, the correct values for these
parameters will depend on whether the mirror is in or out. This should be automatically
sensed by the guider and the appropriate signs applied.
If guide objects are being driven out of the reticles, an error in one of more of these
signs is a prime suspect. |
| E, W, N, & S Backlash: |
These parameters are meant to overcome backlash by providing an additional push on the first
correction following a change in direction. They are
primarily intended for the CAT declination axis, where backlash is severe. |
| Fixed Movement: |
This sets the size of the move, given in pixels on the display (except in the case
of the CAT where miliseconds of motor engagement are used), that the telescope will make
to effect a correction.
This parameter is ignored when using the profile fitting guide
algorithm, which determines the size of the move based on data from the guide object. |
| Scale: |
This sets the plate scale for a given telescope/focus/instrument setup, and also,
in some cases, for the position of the diagonal mirror. These values should be automatically set,
provided the version of the guider appropriate to the
telescope, focus, and instrument has been chosen at startup
DO NOT change these values.
|