SBIG FW8G-Aluma is a self-guiding 8-position filter wheel for the Aluma Series cameras. This wheel has a guiding CCD and associated optics built into the front cover, in front of the filters.
Due to the backfocus requirements, CLA camera lens adapters will not work with this cover. A lower profile standard cover, without guider, is available as an accessory. The standard cover is easily swapped for the self-guiding cover when imaging through a camera lens is desired.
The carousel holds eight 36mm filters and inserts are available for 1.25″ filters. The 36 mm filters provide unvignetted imaging for the largest Aluma sensors.
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.
The FW8G-Aluma includes a built-in focal reducer and autoguider. The pick-off mirror and camera focus can both be adjusted and locked using simple thumbscrews. With the autoguider positioned in front of the filters, optimum guiding sensitivity is provided for all filter slots. Using a built-in autoguider system eliminates issues with flexure, mirror shift, and other mechanical problems that can degrade guiding accuracy.
The FW8G-Aluma is thicker and does not permit use of CLA lens adapters. Interchangeable plates are available to switch your wheel between FW8G and FW8S configuration.