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.



The latest stable release of EQMosaic is available for download at: The EQMOD Sourceforge Project


  1. Double click the file EQMOD_MOSAIC.exe . Depending upon your computer setup the .exe extension may not be visible.
  2. Start your planetarium program (optional) and connect to EQMOD in the “ASCOM Telescope Chooser” dialog. EQMOD will start up.
  3. 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.
  4. Use your planetarium program or the EQMOD slew controls (joystick etc.) in EQMOD to move to the object of interest.
  5. 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).
  6. 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
  1. The first click of the [Spiral] button initializes the spiral slew
  2. Subsequent button clicks slew the scope in a “circular” pattern of grid positions
  3. 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

  1. To change the default settings of EQMOD Mosaic, click the [> > >] button.
  2. 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.
  3. There is a drop down that allows you to save and recall the frame sizes
  4. There is a setting to allow you to specify the amount of overlap between frames.
  5. There is an option to warn you if the slew will cause a mount flip.
  6. There is an option to automatically connect to the default ASCOM driver on program start.
  7. There is an option to keep EQMOD Mosaic on top of all other desktop applications.
  8. 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).
  9. 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


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 


Inidvidual images can be merged using a Mosaic Frame Merge program called IMerge. Which you can download here

Test image:  
Larger Version here:  cs_moonmosaic_large.jpg

Test image version minus the red grid boundaries.
(Click on the larger image link for the setup details). 
Larger Version with Setup Details

More EQMOSAIC Test Images can be found here.