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3.3 The Edit Menu
The edit menu contains functionality to change the state of the program and
data reduction procedures. Features which pertain only to the program and
have little or no impact on the data reduction results have been places
under the Program menu item.
If your system has not been set up, or none of the available configurations
is suitable, you will have to create your own configuration by changing
the data under
Edit :: Telescope parameters and
Edit :: Algorithm parameters
menu items.
At minimum you will need to gather the following
information about your optical system
|
Item. | Menu | When Needed |
|
Telescope diameter | TP | Always |
|
Obscuration ratio | TP | Always |
|
Focus encoder scale | TP | Always |
|
Focus encoder zero | TP | Always |
|
F-Ratio | TP | Always |
|
Pixel Size | TP | Always |
|
Invert image | AP | Always |
|
Manual ef pupil diameter | AP | Always |
|
Ef pupil diameter | AP | If manual true |
|
FITS Focus key | AP | If focus recorded in fits header |
|
|
What the program needs to know about your optical system.
Where TP refers to Edit :: Telescope parameters and AP refers to
Edit :: Algorithm parameters.
It is important to specify numbers as accurately as possible.
In particular you should aim to input the f-ratio and or pupil diameter
accurate to within about 1%. Inaccurate numbers will give progressively
more inaccurate results, but should not lead to catastrophic program
failure.
When you click on the button on the lower toolbar, the program
automatically executes a sequence of data reduction steps.
The default sequence supplied with the system does a good job for
well behaved optical systems.
Under certain circumstances, e.g. a severely rolled edge, you may
wish to define your own data reduction sequence, and add it to the file
ef_sequence.tcl (there is currently no GUI tool to do this for you).
If you have done this you may choose between several available reduction
sequences by invoking the Edit :: Data reduction sequence
and clicking on the desired sequence in the resulting listbox.
By default the following configurations are supplied:
- default
The default sequence for well behaved optical systems.
- hight
Uses a high threshold on the signal clipping level, may be better for
systems with rolled edges, but typically less accurate for well behaved
systems.
- highorder
A continuation of the default sequence which attempts to correct the
extra-focal images up to Zernike 22. If your optical system has
significant high order aberrations, this sequence will give more
accurate results. Note that you must have high quality data to
use this sequence, since it can be unstable with lower quality data.
- lowt
Uses a low threshold on the signal clipping level. For systems with
with very small amounts of wavefront turnover at the pupil edge, this
sequence may prove to be more accurate than the default sequence.
- rolled
A sequence tuned to an optical system with a moderately rolled wavefront edge.
Before proceeding with the calculation of the wavefront,
it is necessary to enter your telescope and camera parameters
into the program. This is done by selecting the
Telescope parameters option under the Edit menu.
These parameters need to be given as accurately as possible.
The one exception to this is the Focus encoder zero (in-focus) position,
for which some latitude is allowable. The program performs
some consistency checks on the values you enter, if the
values appear inconsistent you will be warned at some time during
the computation.
The program assumes that the image corresponding to the extra-focal
plane before focus should have a negative focus offset with respect
to the in-focus position. Depending on the setup of your focus
encoder this may necessitate you entering a negative focus
encoder scale in the entry box labeled
Focus encoder units per m focus.
Parameters controlling the operation of the program are accessed
through the program parameters option under the Edit
menu. Most of these parameters should be self explanatory. If you have
widget help enabled, a short explanation will be posted about each entry.
While most of these settings are not critical, the ones discussed below
must be set correctly.
When the program reduces images, it makes the assumption that
both extra-focal images map to the wavefront in the same way.
It is crucial that the program know if it needs to swap the post
focal image coordinates to match the pre-focus image in order
to validate the congruent coordinate assumption.
This operation is selected by the check-button labeled
Invert one extra-focal image.
If you have taken extra-focal images by a process
equivalent to moving the camera, or telescope focus, you will need
to instruct the program to swap the post focus image coordinates,
since the wavefront coordinates are inverted on passing through focus.
If you have taken extra-focal images using a lens system the post
focus image coordinates should probably not be swapped.
If the initial centering of images is not particularly accurate, both
images may be displaced in the same direction relative to the wavefront
center. Selecting this checkbutton instructs the program to automatically
reject this common mode signal after every iteration.
If this checkbutton is selected, the program checks input parameters
for possible errors. If it looks like some value or combination of
values in unrealistic, a dialog will be displayed which will give you
the choice of continuing or aborting the data reduction. It is
possible that you may intentionally set a parameter outside the range
which the program considers reasonable, for this reason you can turn off
the checking function.
If you are taking extra-focal images by re-focusing or moving your camera
the size of the extra-focal image can be calculated from the
extra-focal distance and the beam f-ratio.
If you are using some optical arrangement to capture extra-focal images
the diameter of the extra-focal image is probably an set by your optics.
Under these circumstances you should set the
Manually set extra-focal-image diameter. radio-button. This will
re-display the algorithm parameters with an extra entry labeled
Extra-focal-image diameter. Enter the appropriate image diameter here.
Note that the only place where the algorithm uses this number is to
calculate the number of pixels across the extra-focal image.
There is no support in this program for using extra-focal images with
dissimilar sampling.
The image parameter editor allows you to specify the focus distance
and the center coordinate of each extra-focal image.
Under normal operation you should not have to use the image parameters
editor.
The image parameter editor allows one to change the focus
distance, and image center coordinates associated with an image.
The focus value for an image may be locked across image loads by using
the lock buttons in the focus edit column.
If your FITS files contain a header key "FOCUS" which indicates
the focus encoder value for the image, this will be loaded
automatically as the focus distance for the image.
If this is not the case you will need to edit these parameters
by hand as explained below.
If the FITS file containing the extra-focal image contains the focus value
associated with a header key string other than "FOCUS", it is still
possible to configure the program to read the focus from the header.
To do this you need to change the contents FITS Focus Key
entry, under the Edit :: Program parameters menu.
Most commonly you will need to use the image parameters editor to specify the
focus distance of each extra-focal image. This will be necessary if the
input image does not contain a FITS header entry giving the focus position,
or if for some reason you need to over-ride this value.
Remember that focus values are supplied in encoder units.
If you wish to specify the distance in meters you should set the values
Edit :: Telescope parameters
Physical size of encoder quanta and Focus encoder zero position to
1.0 and 0.0 respectively.
If you find that you need to enter the same focus value repeatedly, you
can lock the current value specified for an image, using the lock buttons
in the focus edit column. If you use the lock procedure, be very careful
to make sure you load the correct images into each buffer. Running the
program with incorrect focus values will give badly erroneous results.
You should not need to specify the central coordinates of the extra-focal
images, unless the image frame contains multiple images which would
confuse the auto-centering algorithm.
If you find the auto-centering algorithm consistently fails for you, we
would consider this a serious program bug, and would be grateful to
receive an example of an image which causes the failure.
The accuracy of the wavefront reconstruction depends quite critically
on the quality of your extra-focal images. Using this form you
may select pre-processing options to best match your data.
One of the most important parts of pre-processing is to accurately
subtract the background level, so you should pay particular
attention to doing this accurately.
By default if you load a flat field and/or dark frame, these will be
applied to extra-focal images as they are loaded. That is when
an extra-focal image is loaded, the dark frame is first subtracted,
then the result of this subtraction is divided by the flat field.
If you have loaded a flat and/or dark but do not wish them to be
used, you may turn off their use by de-selecting the check-buttons
labeled Subtract dark image and Apply flat field.
The program tries to automatically determine the center of each
extra-focal images. Usually it does a reasonable job. However under
some circumstances the auto-centering may fail, leaving you to
specify the centers in the Edit :: Image Parameters form.
You may prevent the program from attempting to find the image
centers by de-selecting this checkbutton. You can, for instance,
reduce data from a frame containing multiple images as long as you
specify the image positions by hand.
The purpose of the Zernike editor, is to give a general means for
editing the Zernike content of a wavefront before saving it as an
wavefront, image or fringe pattern.
This form implements a filter which transforms the wavefront before it is
saved.
This filter acts independently of the ability to exclude a range of Zernikes
which is provided by the File :: Save Wavefront,
File :: Save Image and File :: Save Fringe forms.
Once set the transformations from this form will be applied to all
wavefronts as they are saved. This is somewhat dangerous if the
user should forget that the wavefront is being transformed. For
this reason the wavefront filter is always set to apply no changes
when the program is first started.
By using the top sub-form you may choose the maximum number of Zernikes
that you wish to edit. In practice you will be limited by screen size
to editing no more than about 30 Zernikes.
By de-selecting the checkbutton labeled Apply these transformations
you may prevent the Zernike editor from applying any changes to the
wavefront. This option may be convenient if you wish to alternately
switch between seeing the raw wavefront (with possibly some low order Zernikes
removed) and seeing the wavefront with some correction applied.
The checkbutton labeled Ignore subtraction range prevents
the editor from subtracting (or zeroing) the range of Zernikes indicated
on the File :: Save ... form.
WARNING: The Zernike editor will remain active even it the
editor form is not displayed.
The Edit :: Graphocity menu item pops up a sub-window containing
several checkbuttons which allow you to control what the program displays
in the display windows. Opting to display less often will speed up the
program, but will of course give you less feedback.
Clicking the right mouse button on one of the display windows
causes a dialog box to pop up. This dialog box allows you to
adjust the gamma3 value for the display. To adjust the gamma
value, move the slider to obtain the desired gamma, then
hit the Redisplay button.
Laplacian Optics Inc. Email: laplace@laplacian.com