Please explain to us about the differences of the Beta 58, Beta 58M and Beta 58A in their specs and performance. Also, please give the differences between the Beta 57 and Beta 57A.
Originally the Beta 58 was available as the the Beta 58C (chrome grill) or the Beta 58M (matte grill). The Beta 58C was eventually discontinued and the Beta 58M became just the Beta 58. The Beta 58 was then discontinued and replaced by the Beta 58A. Beta 58 vs. Beta 58A: Beta 58 vs. Beta 58A - Beta 57 vs Beta 57A.
The difference between the Beta 57 and the Beta 57A is the same as the Beta 58 vs Beta 58A. Beta 57A and Beta 58A Comparison: Beta 57A and Beta 58A Comparison