EQMOD
Mosaic is used to facilitate creating mosaics of large objects. The
program creates a grid of RA and DEC coordinate points so that the
mount can be moved in a systematic manner as the mosaic images are
accumulated.
Double click the file EQMOD_MOSAIC.exe
. Depending upon your computer setup the .exe
extension may not be visible.
Start your planetarium program (optional) and
connect to EQMOD in the “ASCOM Telescope Chooser” dialog. EQMOD will
start up.
In the EQMOD Mosaic window, click the
[Connect] button. EQMOD Mosaic will then connect to an ASCOM driver. If
none has previously been selected then the “ASCOM Telescope Chooser”
dialog will appear. On successful connection the center cell of the
mosaic grid is automatically synchronized with the scopes position and
will appear highlighted.
Use your planetarium program or the EQMOD slew
controls (joystick etc.) in EQMOD to move to the object of interest.
Double click a new grid position (or [Spiral]
button) to slew the mount a precise amount for each subsequent image.
When the scope finishes slewing the target grid cell will be
highlighted and the grid cell label will be displayed (if option
enabled).
If at any point you wish to resynchronize the
grid center with the current scope position, click the [Get Position]
button. The grid will be reset and position F6 (row F, column 6) and
will appear highlighted.
Using
the Spiral Button
The first click of the [Spiral] button
initializes the spiral slew
Subsequent button clicks slew the scope in a
“circular” pattern of grid positions
When all grid positions have been covered the
process starts again. Provided your target is roughly circular/square
and doesn't span the meridian during your imaging session, this
provides a simple one button approach to mosaic building.
Note: The spiral button only becomes
active once a scope is connected its position read. Also the Spiral and
Slew buttons are disabled until the slew is complete.
EQMosaic can also be
used as a spiral search where it is necessary to pause to take an
exposure. This works well for finding dim targets where you need a long
exposure image.
EQMOD
Mosaic Settings
To
change the default settings of EQMOD Mosaic, click the [>
> >] button.
In
this extended window, you can set the frame size that corresponds to
your imaging setup. This setting only needs to be approximate although
it should typically be equal or smaller than the actual camera image
size. The frame size is used by the grid navigator to calculate the
amount of slew.
There
is a drop down that allows you to save and recall the frame sizes
There
is a setting to allow you to specify the amount of overlap between
frames.
There
is an option to warn you if the slew will cause a mount flip.
There
is an option to automatically connect to the default ASCOM driver on
program start.
There
is an option to keep EQMOD Mosaic on top of all other desktop
applications.
The
current default ASCOM driver is displayed and there is a [Choose Scope]
button that allows a different default driver to be selected (perhaps a
driver other than EQMOD).
You
can save and load sessions.
Meridian
Flips
If the Meridian flip
warning option has be enabled, Mosaic will issue a warning if it thinks
the next slew is on the opposite side of the meridian from last slew
position. Mosaic itself doesn't make the mount flip, the driver
actually controls the flip. The mount may not actually flip when you
click the [OK] button because, in the time it takes you to make the
decision, the target position may have drifted back to the mounts
current side.
When doing a mosaic of
an item that starts spanning the meridian, a recommendation would be to
start on the western side and move through the grid by doing columns of
common RA. In this way you spend the maximum amount of time at the same
RA. If the second column is on the other side of the meridian when you
start, then by by the time you've finished imaging the the first
column, the second column may well have drifted across the meridian and
so no flip would be needed.
If you do get the
meridian flip warning in mosaic you can always cancel the slew, wait a
short until the object moves onto the current side of the meridian.
Mosaic Sessions
It is possible to save and load sessions. Up to 10 separate sessions
may be saved and recalled. The following information is saved as part
of a session definition. Prior to saving a session the user can change
the session name by clicking on it, and entering new text.
RA field of view
DEC field of view
RA overlap
DEC overlap
RA & DEC coordinates of grid centre.
X,Y grid coordinates of Cell to be slewed to.
Status of all grid cells.
On session load the grid will be restored to the condition it was in on
saving and a slew is initiated to place the scope at the last slew
position. RA and DEC skip values are recalculated using the current
coordinates.
This feature makes for easier mosaic compilation when imaging spans a
number of observing sessions as the mosaic program is able to pick up
from the exact point it was previously saved.
Additional
Notes
The
settings for EQMOD Mosaic are stored in a file EQMOSAIC.ini in
folder: c:\Documents and Settings\YourLoginName\Application
Data\EQMOD
The
[Get Position] button synchronises the grid to your scope. The object
does not have to be in view when you [Get Position] - when you slew the
grid moves with you where ever you go. Key to mosaic operation is to
realize the difference between 'external' slews (planetarium, tour,
joystick) and Mosaic slews. External slews will move the entire grid
around, Mosaic slew move within the grid.
Tracking:
EQMOD Mosaic can only control the scope to accurately cover an area of
sky if the mount is tracking. The tracking status is checked whenever
the [Get Position] button is pressed and/or at completion of a slew. If
the mount is found not to be tracking then a warning message is
displayed in the message center and an attempt is then made to start
tracking. If this fails a “Scope will not track” message is displayed.
Non-sidereal
tracking: Imaging the Sun and particularly the Moon needs special
consideration Mosaic places a grid on the celestial sphere but objects
such as the Sun and Moon move across that grid with time i.e. move at a
nonsidereal rate. Mosaic incorporates an algorithm that will
automatically compensate for this provided the mount is able to track
the objects accurately . Currently EQMOD only does solar and lunar
tracking in RA - the Moon & Sun both move in declination as
well so over time will slip over mosaic grid. Clearly these are bright
objects and imaging times will not be extended so the effect should be
negligible unless there are long pauses between image captures.
Prior
to initiating a slew Mosaic, checks the scopes current position (both
RA and DEC) and subtracts the position it thinks the scope should be at
(i.e. the position used for the last slew). This gives a drift
compensation in RA and DEC that is then applied to the grid centre
coordinates, from which all other grid cell coords are calculated.
If
you use Mosaic session save/restore and your imaging target is the
Moon, the initial session restore slew is unlikely to get you to the
right place as the Moon will have moved on across the sky. The session
save/load feature is really only practical for Deep Space Mosaics.
Before
starting your Mosaic sequence of images, you can adjust the alignment
of the grid over your object by using the scopes slew controls. For
example: Whilst imaging the moon, try centering the moon and click the
[Get Position] button to lock the grid in place. Then double click
around the grid to find the frames the will constitute the boundaries
of the mosaic. If any frames on the edge have an unacceptably small
amount of moon in them, simply use the telescope slew controls to get
more of the moon in the cell and the drift compensation code will
automatically move the grid centre to compensate. Then check that the
other extremity is satisfactory. This way, you can ensure that you
capture the object with the minimum number of images.
CAMERA
ALIGNMENT
Usually it
makes sense to have your imaging camera aligned orthogonally with the
mount RA and DEC axis. If this is not the case mosaics can still be
built but you may need to increase the amount of overlap to prevent
gaps appearing.
Camera
aligned othogonally with RA/DEC axis, 10% overlap
45
degree alignment error, 10%
overlap
Camera
at 45 degrees, 25%overlap
MERGING
IMAGES
Inidvidual images
can be merged using a Mosaic Frame Merge program called IMerge. Which
you can download here
