09-23-2010, 03:44 PM
[quote name='Brightcolours' timestamp='1285254090' post='3171']
It is just a fact, that lenses and their motors/electronics/software are geared towards responding to commands from the PD-AF systems. They can make "steps" which are geared towards being able to see phase difference as quick as possible. And they can respond to "move x amount" and to "move to there".
Contrast AF works different, it just needs a lens to move relatively slowly until it sees contrast going worse again. Then it knows it reached focus.
To achieve this with the PD AF lenses is difficult, the implementations of how the motor is being commanded is just so very different. That is why with ALL manufacturers, we see comparatively slow AF, we see the lenses take actual small steps towards focus and beyond and back. While the manufacturers with the same image processors achieve contrast AF fast and fine with their compact digitals.
Nikon, Canon, Pentax, Olympus, all show slow AF in contrast AF with PD-AF lenses.
Sony does not offer contrast AF, with live view via the main sensor they chose to only offer MF (A5X0 series).
The Sony NEX series does not AF at all with the Sony PD-AF lenses, even when they are SAM or SSM lenses.
Olympus with micro 4/3rds only offers fast contrast AF with the new micro 4/3rds lenses, the older PD-AF lenses either do not AF at all, or offer a slower contrast AF performance.
It is just that way, Wim... lenses designed to respond to a PD-AF protocol (or in-body motors/AF electronics (Pentax, Sony, Nikon) do not offer the right set of commands to allow for fast contrast AF.
I think it would be possible to design a Nikon in-body lens motor+AF electronics that would be both able to drive the AF optimized for contrast AF and for PD-AF (with lenses that use the internal motor).
[/quote]
Thank you for that extensive explanation, Brightcolours.
I do think however that in the case of Canon the slow C-AF is mainly due to the fact that Canon cameras just aren't optimized to do this type of sensor-based AF yet. If I see how the 85L II focuses f.e., I think it should be very feasible to use the same mechanism for C-AF without a problem, and faster with any other USM lens, provided the camera has a good C-AF system which can operate, ideally, independent from the way the sensor normally works.
Kind regards, Wim
It is just a fact, that lenses and their motors/electronics/software are geared towards responding to commands from the PD-AF systems. They can make "steps" which are geared towards being able to see phase difference as quick as possible. And they can respond to "move x amount" and to "move to there".
Contrast AF works different, it just needs a lens to move relatively slowly until it sees contrast going worse again. Then it knows it reached focus.
To achieve this with the PD AF lenses is difficult, the implementations of how the motor is being commanded is just so very different. That is why with ALL manufacturers, we see comparatively slow AF, we see the lenses take actual small steps towards focus and beyond and back. While the manufacturers with the same image processors achieve contrast AF fast and fine with their compact digitals.
Nikon, Canon, Pentax, Olympus, all show slow AF in contrast AF with PD-AF lenses.
Sony does not offer contrast AF, with live view via the main sensor they chose to only offer MF (A5X0 series).
The Sony NEX series does not AF at all with the Sony PD-AF lenses, even when they are SAM or SSM lenses.
Olympus with micro 4/3rds only offers fast contrast AF with the new micro 4/3rds lenses, the older PD-AF lenses either do not AF at all, or offer a slower contrast AF performance.
It is just that way, Wim... lenses designed to respond to a PD-AF protocol (or in-body motors/AF electronics (Pentax, Sony, Nikon) do not offer the right set of commands to allow for fast contrast AF.
I think it would be possible to design a Nikon in-body lens motor+AF electronics that would be both able to drive the AF optimized for contrast AF and for PD-AF (with lenses that use the internal motor).
[/quote]
Thank you for that extensive explanation, Brightcolours.
I do think however that in the case of Canon the slow C-AF is mainly due to the fact that Canon cameras just aren't optimized to do this type of sensor-based AF yet. If I see how the 85L II focuses f.e., I think it should be very feasible to use the same mechanism for C-AF without a problem, and faster with any other USM lens, provided the camera has a good C-AF system which can operate, ideally, independent from the way the sensor normally works.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....