[quote name='popo' timestamp='1305238913' post='8278']
To clarify, yes, I was trying to say if DSLR contrast AF could be speeded up if they sample faster in a similar way to how Panasonic describe. I'm assuming the DSLR sampling rate will be at most that provided by the video modes, or up to 60fps typically.
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It is not the sample rate that makes contrast detect AF with PD -AF systems slower, but rather the motor electronics/management of the lens which is designed for PD-AF.
Put a 4/3rds lens on a micro 4/3rds camera, and you will see the same thing... Panasonic can be that fast because the lenses are designed with the contrast detect AF system from panasonic in mind. Only with micro 4/3rds lenses.
[quote name='Brightcolours' timestamp='1305240259' post='8279']Put a 4/3rds lens on a micro 4/3rds camera, and you will see the same thing... Panasonic can be that fast because the lenses are designed with the contrast detect AF system from panasonic in mind. Only with micro 4/3rds lenses.[/quote]
According to PZ the Pana/Leica 25 mm f1.4 may be the only exception: "The lens may also be interesting for micro four-thirds users - the AF remains functional when using one of the Olympus/Panasonic adapters. The AF speed is fine here." As far as I know AF of all other FT lenses is sluggish on MFT cams (if it works at all).
[quote name='popo' timestamp='1305200891' post='8253']
Definitely interesting, but perhaps over-simplified. Did they do a similar comparison chart for AF accuracy of a moving target? <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/tongue.gif' class='bbc_emoticon' alt='  ' />
[/quote]
Agreed... Way too over-simplified... Measuring AF accuracy in a decent quantitative way and puting results on a graph (like these unbelievably nice looking curves) seems to be unrealistic to me. CD part might be OK because it's their system, and they have a specific way to measure it. But what about the counter part? Which PD AF, what kind of a scene is it, are there moving subjects etc...
Serkan
[quote name='PuxaVida' timestamp='1305269883' post='8285']
Agreed... Way too over-simplified... Measuring AF accuracy in a decent quantitative way and puting results on a graph (like these unbelievably nice looking curves) seems to be unrealistic to me. CD part might be OK because it's their system, and they have a specific way to measure it. But what about the counter part? Which PD AF, what kind of a scene is it, are there moving subjects etc...
Serkan
[/quote]
As far as PD AF is concerned you can simply try it yourself. Choose manual focusing, then check the focus -range- where the in-focus indicator is active. At the end of the day this is also the range which is considered to be Ok by the PD AF. It is the same focus check mechanism after all.
PD AF is also performed at max. aperture so it is vulnerable to focus shifts when stopping down (residual spherical aberration).
The Panasonic illustration is not scientifically correct though because the various PD AF have all different characteristics, of course. From a qualitative point of view it is absolutely valid though.
[quote name='Klaus' timestamp='1305278671' post='8286']
PD AF is also performed at max. aperture so it is vulnerable to focus shifts when stopping down (residual spherical aberration).
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Contrast AF isn't necessarily immune to focus shift either, although right now it is theoretical than practical. Maybe the Panasonic implementation is different, but on Olympus it feels like it uses the widest aperture during AF while maintaining a reasonable exposure.
Taking a step back, given that Panasonic use contrast AF, it is in their interested to promote the possible advantages that gives, while they may play down or ignore any disadvantages in the marketing material. Personally I don't care what the method is, as long as it is fast enough and accurate enough.
Fuji used a hybrid method of both phase and contrast (both on sensor) in some of their recent compacts, although they have a lot of work still to do based on reviews. It could be one future path for the best of both worlds though.
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[quote name='Klaus' timestamp='1305278671' post='8286']
As far as PD AF is concerned you can simply try it yourself. Choose manual focusing, then check the focus -range- where the in-focus indicator is active. At the end of the day this is also the range which is considered to be Ok by the PD AF. It is the same focus check mechanism after all.
[/quote]
I see, but, what if the subject is moving towards / away from the camera... Would we have the same curves?
Quote:PD AF is also performed at max. aperture so it is vulnerable to focus shifts when stopping down (residual spherical aberration).
I don't get it Klaus... Does G3 performs AF right after closing the aperture? Because the less amount of light gathering would not help with CD AF either, isn't that right?
Serkan
> I see, but, what if the subject is moving towards / away from the camera... Would we have the same curves?
This would be about the accuracy of the AF prediction. CD AF is surely worse here so far but it seems to catch up.
Can it reach or overtake PD AF ? No idea. I wouldn't sign this with blood. At some stage it is a viable question whether it's "good enough".
> I don't get it Klaus... Does G3 performs AF right after closing the aperture? Because the less amount of light gathering would not help with CD AF either, isn't that right?
I don't know whether the G does that but technically it can close the aperture and focus thereafter. It just need to perform an contrast analysis of sensor data. The effective aperture should be rather irrelevant here (within limits depending on the light level).
[quote name='Klaus' timestamp='1305294750' post='8292']
I don't know whether the G does that but technically it can close the aperture and focus thereafter. It just need to perform an contrast analysis of sensor data. The effective aperture should be rather irrelevant here (within limits depending on the light level).
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I know for sure Sony Nex always close/open the aperture real time when you change the aperture. That's why they don't need DOF preview button too.
[quote name='Klaus' timestamp='1305294750' post='8292']
...
I don't know whether the G does that but technically it can close the aperture and focus thereafter. It just need to perform an contrast analysis of sensor data. The effective aperture should be rather irrelevant here (within limits depending on the light level).
[/quote]
Apart from the light gathering and the impact of this on CD, the contrast analysis by checking the daha of adjacent pixels on sensor would be different if the aperture was closed for a lens with RSA problem... Therefore I think having and advantage in terms of RSA requires closing of aperture right before performing AF... Or am I missing something?
Serkan
[quote name='PuxaVida' timestamp='1305365847' post='8312']
Apart from the light gathering and the impact of this on CD, the contrast analysis by checking the daha of adjacent pixels on sensor would be different if the aperture was closed for a lens with RSA problem... Therefore I think having and advantage in terms of RSA requires closing of aperture right before performing AF... Or am I missing something?
Serkan
[/quote]
Yes, you are missing something. I don't know how pana/oly cameras behave, but on Sony Nex cameras, the aperture is always closed (all the time) to whatever aperture you set it. It's never wide open, unless you set it wide open. (that's true for native e-mount lenses, not for A-mount lenses with the adapter). That's how it works in video and stills (that is liveview on dslrs). And there is AF in video mode too.
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