Mosaic planner: how many panels for a large target
Enter the area to cover (or pick a target) with your camera, telescope and overlap. The planner works out panels across and down, tries the camera in both orientations, and draws the panel grid over the target's catalogue outline.
How the planner counts panels
Along each direction, the first panel covers one field width and every additional panel adds a field width minus the overlap. The number of panels is the smallest count whose coverage reaches the size of the area:
panels = 1 + ⌈ (area − field) ÷ (field × (1 − overlap)) ⌉ (1 when the area fits in one field)
The planner does this for the width and the height, multiplies the two, and then repeats the calculation with the camera turned 90°. It keeps whichever orientation needs fewer panels. For long, thin areas, turning the camera often saves a whole row.
The fields come from your sensor and focal length with the exact 2 × arctan formula of the field of view calculator, and the finished mosaic size in pixels is the covered area divided by the image scale.
Choosing the area
Picking a target fills in its catalogue size plus 10 % on each axis. You can type any width and height instead, for example to include a neighbouring object or more surrounding sky. Catalogue sizes are often single diameters or the bright parts of a nebula; the target pages list the values from each catalogue so you can choose a size that matches what you want in the picture.
Worked example: the Veil Nebula
SIMBAD gives the Cygnus Loop as 230′ × 160′. With a 10 % margin, the area is about 253′ × 176′. With an APS-C IMX571 sensor and 15 % overlap:
| Focal length | Field per panel | Panels | Layout |
|---|---|---|---|
| 250 mm | 322.8′ × 215.8′ | 1 | single frame |
| 400 mm | 201.8′ × 134.9′ | 3 | 3 × 1, camera turned 90° |
| 550 mm | 146.8′ × 98.1′ | 4 | 2 × 2 |
At 400 mm the unrotated layout would need 2 × 2 = 4 panels; turning the camera to portrait covers the height with one panel and needs three across. That is the kind of saving the orientation check finds.
Overlap
Overlap gives the stitching software shared stars to align neighbouring panels, and it absorbs small pointing errors when the mount slews between panels. The planner defaults to 15 %. More overlap costs panels: in the example above, 30 % overlap at 550 mm needs eight panels (4 × 2, camera turned) instead of four.
Time and storage
A mosaic multiplies everything per panel: if each panel needs four hours to reach the depth you want, a four-panel mosaic needs sixteen. It multiplies data volume in the same way; the storage calculator estimates the disk space for each panel’s session.
Limits of the model
The planner lays panels on a flat grid. For areas larger than about 10° the curvature of the sky starts to matter, and planetarium or capture software with a mosaic planner that works on the sphere is the better tool. Panels are also assumed to share one camera orientation; some imagers rotate individual panels to follow a curved object, which the grid does not model.
Questions
- How many panels do I need for the Veil Nebula?
- With an APS-C IMX571 camera, a 10 % margin around SIMBAD's 230′ × 160′ outline and 15 % overlap: one frame at 250 mm, three panels at 400 mm and four at 550 mm.
- Does a mosaic need more imaging time?
- Yes. Each panel needs its own integration to reach the same depth, so total time grows roughly in proportion to the number of panels.
Sources
- Cygnus Loop (NAME Cyg Loop) in SIMBAD CDS, Strasbourg. Accessed October 12, 2026.