New 50 1.8 STM questions

mbv wrote:

Bought a new 50 1.8 STM at a local "brick and mortar" store for ease of exchange/return in case smth is wrong. So far very pleased with the optical performance of the lens at or near wide open --- for sure beats my 20+ -years-old 50 1.8 II. However I am still trying to figure out two quirks, wondering if they are specific to this particular copy, or are generic "features".

1. When focusing manually there is a sound (not loud, but still well audible) like there is a tiny gear train spinning. Is this normal? My other two STMs 10-18 and 55-250 are absolutely silent. Although I understand that they are internal focusing while 50 1.8 is focusing by extension, I did not expect this.

2. My old 50 1.8 II is hopelessly inconsistent when focusing in the VF mode. I expected the new STM to be much better. It is indeed better, but not entirely perfect: wide open at 1.8 the focusing target is always, or almost always, within the DOF, but sometimes the bulk of DOF is behind the target and sometimes it is in front. This is on my 70D with focusing by the central point at a typical distance of 8 - 10ft or so. (Tests of MFA actually resulted in zero adjustment needed for this lens. Anyways, there seems to be no focusing bias - just a shot to shot variation.) Is my expectation for a better focusing consistency too high?

Thanks in advance for any input.

1. Yes this is normal.

2. Assuming this is not user error and you have tested properly on a tripod with a remote shutter etc then return the lens. This is one of my most accurate lenses and from what i've seen most people have found the same, especially in low light. In terms of AF accuracy it's on par with my L lenses.