Live Composite Star Trail Planner
Live Composite is the Olympus and OM System mode that builds a star trail in real time, adding only new light so the sky never blows out. This planner works out how many frames you need, the exposure per frame, and roughly how long your trails will be for any focal length and total shooting time.
All these bodies support Live Composite.
Max 60s in Live Composite.
Frames to set
Trail length
across the frame width
Frame coverage
horizontal field of view
How far stars travel
The sky rotates 15 degrees per hour at the celestial equator. The table shows how much of the frame a star near the equator sweeps across in one hour at each focal length. Point closer to the pole and trails are shorter and more curved.
| Focal length | Horizontal FOV | 1 hr trail (equator) |
|---|---|---|
| 8mm fisheye | 94.5° | 16% of width |
| 12mm | 71.6° | 21% of width |
| 17mm | 53.9° | 28% of width |
| 25mm | 38.2° | 39% of width |
| 45mm | 21.8° | 69% of width |
What Live Composite does
Live Composite is a mode on Olympus and OM System cameras built for exactly this kind of shot. It takes a series of frames at a fixed exposure and stacks them, but instead of brightening the whole image with each frame, it only adds pixels that are brighter than what is already there. The result is that the sky background and foreground stay at the brightness of the first frame while the moving stars draw bright trails on top. You can watch the trails build on the screen in real time and stop when you like.
This solves the classic star-trail problem. The old method was either one extremely long exposure, which blows out the sky and the foreground, or shooting dozens of separate frames and stacking them later in software. Live Composite does the stacking in the camera, with no post-processing required and no risk of overexposure no matter how long you run it.
How this planner calculates
- Frames to set is simply your total duration divided by the seconds per frame. In Live Composite you choose the per-frame exposure, then let it run; the frame count here tells you how long to leave it going to reach your target duration.
- Trail length comes from the rotation of the sky. Stars move 15 degrees per hour at the celestial equator, scaled by how close you point to the pole. That angular travel is compared to your lens's field of view to show how far across the frame a trail will stretch.
- Seconds per frame is capped at 60, the limit for Live Composite and the other computational modes. The per-frame exposure controls brightness, not trail length; trail length depends only on the total duration.
Where you point matters
Stars near the celestial equator move the fastest and draw the longest, straightest trails. Stars near the celestial pole barely move and draw short, tight curves. If you frame on Polaris in the northern hemisphere, the trails become concentric circles around a near-stationary point, which is the classic circular star-trail look. Pointing toward the equator instead gives long sweeping arcs. This planner lets you pick a rough pointing direction so the trail-length estimate reflects it.
Suggested starting settings
A common starting point is ISO 800, f/2.8, and 20 to 30 seconds per frame, then adjust for your sky brightness on the first frame. Because Live Composite locks exposure to that first frame, get it right before you commit: expose so the foreground and sky look correct, then let the stars accumulate. A wide lens such as a 12mm or the 8mm fisheye keeps a large area of sky in view, which suits long trails. For nailing focus on the stars in the dark, OM System and Olympus bodies with Starry Sky AF do it automatically.
This planner covers the trail geometry and the frame count. For a single untracked exposure where you want pin-point stars rather than trails, use the Astro Exposure Calculator instead.