Re: A Bit More About the New Big White Lenses That Are Coming
Just to share on this thread...
There are 2 technologies that are recently being discussed and they need to be understood to have an intelligent conversation -
1) DPAF
2) STM motors.
DPAF delivers all the additional benefits of focusing that was being sought. Each pixel pair is able to determine if focus is in front or behind and by how much (see Canon's site). Quad or multi pixel does not give any AF advantage more than what DPAF gives.
STM motors have defined steps, each step is a fixed angle from which the focus distance is known ahead of time. With the information that the DPAF can collect, the DIGIC processor can send information to the lens to smoothly and in a straightforward manner focus the lens. Albeit, a STM is slower than the USM motor. So STM works well with DPAF, or conversely, DPAF's additional information can be precisely used by STM lenses.
USM motors need a more complex algorithm to focus and needs to hunt to focus. This need to hunt (backwards /forwards) movement creates challenges for heavy focus lens groups that have inadequate motors.