Peter,
The smaller 1.25" filter screw-in type reducers you may have seen, are achromatic doublets and were initially designed for use with small chipped webcam to give a wider field of view.
The larger Celestron/ Meade reducers were designed for SCT's.
Yes, there's always a compromise... there will be some chromatic aberrations (minor) and some field distortion (lack of flat field).
|