I own a Minolta MD 100-300mm f 5.6 zoom. It has f stops from 5.6 to 32 plus the lug allowing it to work on Program (X-700). I've always assumed it was a constant f stop throughout the zoom range as nothing on it indicates that it is a 5.6 - 6.3.(even metering while zooming produces no noticeable change on my in-camera readout) I've recently seen advertised used lenses that indicate they are variable f stop (5.6 - 6.3). Can anyone confirm that there are actually two different versions of this lens? I'm quite satisfied with the quality of mine but would be interested to hear about your experiences with it/them. One source claims the non-variable lens to be 'rare'. (not to be confused with higher quality) Best, LM.