06-07-2012, 03:42 PM
[quote name='Brightcolours' timestamp='1339073516' post='18741']
USM does not react fast enough for the small steps contrast detect needs. It is not about speed but the way the motors are being used. USM is fine for PD AF use, where the motor does not have to stop moving for focus check.
As I said, this is the reason Olympus uses MSC motors in the contrast AF based MFT lenses, and not the SWD motors (USM clones) they used in PD AF DSLRs.
http://www.olympus.com.au/Learn---Explor...ology.aspx
[/quote]
If you look at the description of the Olympus technology, the key emphasis is put on a totally new lens design (compared to the previous lens), where now only a single small lens needs to be moved to reduce mass to an absolute minimum. "Low focusing optical mass for extremely fast moving speed and precise control".
This seems to be the most important aspect. Sure, there is also the "High speed drive motor with precise stop-start control characteristics". But I am wondering there if that motor is indeed faster than a USM motor.
The key question, as you put it, is what is the lag of the system. Does it take a while for the USM to get up to speed, so to speak. I actually don't think so. Piezo is extremely fast responding. The issue could be the "ring" USM, which may cause the whole system to have a larger mass since it's made as a ring around the lens. But a micro USM, like Canon uses in the 50mm f1.4 should do the job, if it's only a mass issue.
USM does not react fast enough for the small steps contrast detect needs. It is not about speed but the way the motors are being used. USM is fine for PD AF use, where the motor does not have to stop moving for focus check.
As I said, this is the reason Olympus uses MSC motors in the contrast AF based MFT lenses, and not the SWD motors (USM clones) they used in PD AF DSLRs.
http://www.olympus.com.au/Learn---Explor...ology.aspx
[/quote]
If you look at the description of the Olympus technology, the key emphasis is put on a totally new lens design (compared to the previous lens), where now only a single small lens needs to be moved to reduce mass to an absolute minimum. "Low focusing optical mass for extremely fast moving speed and precise control".
This seems to be the most important aspect. Sure, there is also the "High speed drive motor with precise stop-start control characteristics". But I am wondering there if that motor is indeed faster than a USM motor.
The key question, as you put it, is what is the lag of the system. Does it take a while for the USM to get up to speed, so to speak. I actually don't think so. Piezo is extremely fast responding. The issue could be the "ring" USM, which may cause the whole system to have a larger mass since it's made as a ring around the lens. But a micro USM, like Canon uses in the 50mm f1.4 should do the job, if it's only a mass issue.