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Author Topic: Phase One XF Focus Lock feature/Hassy True Focus?  (Read 2227 times)

william

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Phase One XF Focus Lock feature/Hassy True Focus?
« on: April 18, 2016, 09:11:29 pm »

In the discussions of the Hassy H bodies and the Phase XF, Hassy's True Focus feature is often mentioned as a significant advantage over the Phase.

In perusing the XF manual, I came across the following:

"AF-Lock:
When the camera is set to either the Single shot or Continuous AF Drive mode, the focus position can be locked, which is useful for off-center subjects. The AF-Lock function is not assigned to a control button by default. To re- configure the front or rear user button, or assign the feature to the secondary shutter release button, press the Rear Key and select UI Setup > Control Setup > Rear / Front / 2nd Shut > AF lock.
1. Focus on the subject using the Single shot or Continuous AF Drive mode.
2. Press and hold the assigned button to lock the focus.
3. Recompose the subject in the viewfinder."

I haven't (yet) used the XF and I've never used the Hassy H, so someone correct me if I'm wrong, but:

I am assuming this focus lock feature doesn't work the same as True Focus. That is, I'm assuming that True Focus actually refocuses the lens after you do "focus and recompose" in order to compensate for "yaw" (or whatever is the correct term). Whereas, presumably, the XF's focus lock is like the focus lock on my Nikons: it holds the selected focus position, but does not actually refocus the lens to account for vertical or horizontal rotation as a result of "focus and recompose". All correct?

If so, then: wouldn't it be a fairly straightforward software/firmware matter, given that the ability to "store" a certain focal distance via focus lock is already built in, to update the focus lock feature to incorporate True Focus-like functionality? That is, a new instruction/function and menu item essentially telling the camera "when Focus Lock has been activated and "Adjust for Yaw" is turned on, adjust the lens to remain focused on the originally-selected and locked focus point."

What am I missing? One would think if it were this easy, every camera offering a focus lock feature (including my Nikons and Leica S) would incorporate this functionality...
« Last Edit: April 18, 2016, 09:39:05 pm by william »
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eronald

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Re: Phase One XF Focus Lock feature/Hassy True Focus?
« Reply #1 on: April 18, 2016, 09:47:35 pm »

In the discussions of the Hassy H bodies and the Phase XF, Hassy's True Focus feature is often mentioned as a significant advantage over the Phase.

In perusing the XF manual, I came across the following:

"AF-Lock:
When the camera is set to either the Single shot or Continuous AF Drive mode, the focus position can be locked, which is useful for off-center subjects. The AF-Lock function is not assigned to a control button by default. To re- configure the front or rear user button, or assign the feature to the secondary shutter release button, press the Rear Key and select UI Setup > Control Setup > Rear / Front / 2nd Shut > AF lock.
1. Focus on the subject using the Single shot or Continuous AF Drive mode.
2. Press and hold the assigned button to lock the focus.
3. Recompose the subject in the viewfinder."

I haven't (yet) used the XF, so someone correct me if I'm wrong, but I am assuming this focus lock feature doesn't work the same as True Focus. That is, I'm assuming that True Focus actually refocuses the lens after you do "focus and recompose" in order to compensate for "yaw" (or whatever is the correct term). Whereas, presumably, the XF's focus lock is like the focus lock on my Nikon D800: it holds the selected focus position, but does not actually refocus the lens to account for vertical or horizontal rotation as a result of "focus and recompose".

All correct? If so, then: wouldn't it be a fairly straightforward software/firmware matter, given that the ability to "store" a certain focal distance via focus lock is already built in, to update the focus lock feature to incorporate True Focus-like functionality? That is, a new instruction/function and menu item essentially telling the camera "when Focus Lock has been activated and "Adjust for Yaw" is turned on, adjust the lens to remain focused on the originally-selected and locked focus point."

What am I missing?

You're missing the geometry. To get focus and recompose to work  one needs an accurate measurement of the swing angle, and the lenses need some form of calibration. I don't think this whole business is rocket science, frankly, but making it work reliably needs a decent sensor in the body, and the programming is probably quite hard for a small team and then there are those horrible two letters: I and P.

There are probably other ways to skin this cat. Sony sensors have focus pixels all over them these days, and I think Phase is counting on this in the future. Panasonic infers AF from the defocus pattern. And of course the simplest commercial solution is to get the dealers to convince customers that this issue doesn't matter in their shoots, which is something Phase seems to have managed quite well so far.

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yashima

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Re: Phase One XF Focus Lock feature/Hassy True Focus?
« Reply #2 on: April 18, 2016, 10:05:42 pm »


I think William's understanding is correct. XF Focus lock is simply keeping a fixed focal distance.

Anyone please enlighten me why it is so hard to make multiple focus point with MF sensor? It has been in FF for over 15 years.
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NickT

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Re: Phase One XF Focus Lock feature/Hassy True Focus?
« Reply #3 on: April 18, 2016, 10:09:44 pm »

You are correct that Phocus uses accelerometers to measure swing and tilt and once the shot is re-composed adjusts the focus to compensate for the change in distance.
 I was a very early beta tester of true focus and use it all the time.

As for the Phase it does sound like they are using focus re-compose ala Nikon and without any compensation.

It's possible that there are patent issue discouraging Phase from adopting a similar technique just as I'm sure Phase one have proprietary technology that hasselblad couldn't adopt.
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NickT

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Re: Phase One XF Focus Lock feature/Hassy True Focus?
« Reply #4 on: April 18, 2016, 10:12:15 pm »


Anyone please enlighten me why it is so hard to make multiple focus point with MF sensor? It has been in FF for over 15 years.

I have asked the product manager at Hasselblad about this many times and the answer is that it is indeed hard. AFAIK the only FF AF sensors available  are from Minolta if I remember correctly and the AF points are just too close to the centre. I even asked if they could put two 35mm sensors in but that apparently is difficult too... I might ask again!
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