Aluma wheels include a positive centering mechanism that precisely centers each filter in the exact same position every time. This single-pixel accuracy completely eliminates ghost images of dust spots and other artifacts after flat-fielding.
The left-hand image below shows a dust spot on the filters. A flat-field calibration frame was taken, then the filter wheel was rotated several times before taking a second picture, which was flat-field calibrated, at right. No evidence of the dust spot is visible. This high precision results in the highest quality images and excellent photometric accuracy.