Star Trackers & Long Exposures: How to Turn the Earth Off

Why does a tracker matter? It's simple math.

Untracked (Static Tripod): You are limited by the NPF Rule or 500 Rule. With a 50mm lens, you might get 8 seconds before stars streak. You have to crank your ISO to 3200 or 6400, adding noise.

Tracked: With a tracker, you can shoot that same 50mm lens for 120 seconds.

• You capture 15x more light per frame.
• You can drop ISO to 800 or 1600 (less noise).
• You can stop down the aperture (e.g., f/2.8 to f/4) for sharper stars.

There are two main categories of portable star trackers:

1. The Ultra-Portable (Mechanical or Basic Electric) Example: Move Shoot Move (MSM) Rotator

• Pros: Tiny, fits in a jacket pocket, quick setup.
• Cons: Less accurate for focal lengths over 50mm.
• Best For: Wide-angle milky way landscapes.

2. The Astrophotography Workhorse Example: Sky-Watcher Star Adventurer GTi

• Pros: GoTo capability (finds targets for you), handles 300-400mm lenses, built-in guiding port.
• Cons: Larger, heavier, needs a counterweight.
• Best For: Deep sky imaging with telephoto lenses.

A tracker only works if its axis is perfectly parallel to Earth's axis.

Northern Hemisphere: You align to Polaris (the North Star). It's not exactly at the pole, so you use the tracker's polar scope clock face to offset it correctly.

Southern Hemisphere: You align to... nothing. There is no south star. You have to triangulate using the Sigma Octantis constellation (which is incredibly faint). Pro Tip: Use a digital inclinometer or a "polemaster" camera to assist if you can't see the pole stars.

Once you are tracking, your settings change completely from static shooting.

• Mode: Bulb
• Aperture: Stop down one click (e.g., f/1.8 -> f/2.2) for sharpness. You have the time now!
• ISO: 800 to 1600 (ISO Invariance sweet spot for most sensors).
• Shutter: 60s to 120s (use an intervalometer).

Check your Histogram: You want the "mountain" of data to be roughly 1/3rd from the left. Not crushing the blacks, but not blown out.