When using an Alt-Azimuth mount for astrophotography, you might notice your images slowly spinning or blurring during long exposures. This effect is called field rotation.
Because Alt-Az mounts move in two perpendicular directions (altitude and azimuth), they can’t perfectly compensate for Earth’s rotation, causing the sky to appear to rotate in your camera’s field of view.
To overcome this, astrophotographers often use a field rotator accessory or switch to an equatorial mount, which tracks stars by rotating along Earth’s axis, eliminating field rotation.