How is the field of view calculated?

Field of view in degrees equals the arctangent of the sensor dimension over twice the focal length, doubled, converted to degrees. A common approximation is 57.3 times sensor size divided by focal length, which the tool uses in its full trigonometric form for accuracy across wide fields.

Why do mosaics need overlap?

Overlap gives the stacking software shared stars to register and blend adjacent panels seamlessly, and it covers vignetting and edge distortion that you crop away. Without overlap, gaps or hard seams appear between panels. Fifteen to twenty-five percent is the usual range.

How does overlap change the panel count?

Each panel only contributes its effective field of view, which is the full field times one minus the overlap fraction. The tool divides the target size by that effective field and rounds up, so higher overlap means more panels to cover the same area.

What target size should I enter?

Use the angular size of your subject in degrees. For example, the North America Nebula spans roughly 2 by 2 degrees, the Andromeda Galaxy about 3 by 1 degrees. Add a little margin so the target is comfortably framed rather than touching the edges.

Does this account for sensor orientation?

It assumes the sensor's width maps to the target's width and its height to the target's height. If you rotate the camera, swap your sensor width and height inputs. Planning in the orientation you will actually shoot gives the correct column and row counts.

Astrophotography Mosaic Panel Calculator

Imaging a target larger than your sensor’s field of view means shooting a mosaic — a grid of overlapping panels stitched into one frame. This planner computes your single-frame field of view from the sensor and focal length, then works out how many columns, rows, and total panels you need to cover the target with your chosen overlap.

How it works

Field of view for each sensor axis is found by trigonometry, then each panel’s effective coverage is reduced by the overlap so adjacent frames share a margin:

FOV_deg       = 2 × atan(sensor_mm / (2 × focal_mm)) × 180/π
effective_FOV = FOV_deg × (1 − overlap_fraction)
columns       = ceil(target_width_deg  / effective_FOV_width)
rows          = ceil(target_height_deg / effective_FOV_height)
panels        = columns × rows

The arctangent form stays accurate even for wide-field optics where the simple small-angle approximation drifts.

Example and tips

A full-frame 36 × 24 mm sensor at 500 mm focal length yields a field of view of about 4.1 × 2.7 degrees. Covering a 6 × 4 degree region with 20 percent overlap needs effective panels of roughly 3.3 × 2.2 degrees, giving ceil(6/3.3)=2 columns and ceil(4/2.2)=2 rows — a 2 × 2, four-panel mosaic. Add margin to your target size so stars do not crowd the edges, and keep overlap consistent so the stitching software has reliable registration stars between every panel.