<Dl> <Dd>... 16 / 13 °, 20 / 14 °, 25 / 15 °, 32 / 16 °, 40 / 17 °, 50 / 18 °, 64 / 19 °, 80 / 20 °, 100 / 21 °, 125 / 22 °...</Dd> </Dl> <Dd>... 16 / 13 °, 20 / 14 °, 25 / 15 °, 32 / 16 °, 40 / 17 °, 50 / 18 °, 64 / 19 °, 80 / 20 °, 100 / 21 °, 125 / 22 °...</Dd> <P> while shutter speeds in reciprocal seconds have a few conventional differences in their numbers (1 / 15, 1 / 30, and 1 / 60 second instead of 1 / 16, 1 / 32, and 1 / 64). </P> <P> In practice the maximum aperture of a lens is often not an integral power of 2 (\ displaystyle \ scriptstyle (\ sqrt (2))) (i.e., 2 (\ displaystyle \ scriptstyle (\ sqrt (2))) to the power of a whole number), in which case it is usually a half or third stop above or below an integral power of 2 (\ displaystyle \ scriptstyle (\ sqrt (2))). </P>

Differences in exposures are noticeable at 1/3 of a stop