Observations of the Phase XF autofocus

[DrakeJ]

I'm curious what other users have observed regarding the autofocus on the XF when shooting people. So I'll begin sharing my experience:

First off, spot focus or average focus. In my testing spot focus wins hands down. Average does not give me a good hit rate when I go short DoF. So in essence, I make sure to always be in spot focus mode.

I have some issues with getting false focus confirms and when a false confirm happens it always back focuses. However, it's really not that much of an issue because when it happens it's clearly visible in the viewfinder and contrast on the subject is low, so I can forgive this behaviour.

Calibrating the lenses have proven to be difficult, not with longer lenses but 80mm and wider. When using a LensCal Spyder that is well lit the XF back focuses when the lens is set to close focus, and front focuses when set to infinity. It instantly finds focus, but moves to the point where it's just in focus, but really it should hop back a smidge to be in perfect focus. This does not happen if the throw is short or if the contrast is bad since it then will try harder to get in perfect focus.

Hard to explain the last one, but knowing this, if I know the focus throw is long and my subject is well lit, I double tap to be sure that I'm perfectly in focus. With the above knowledge, my hit rate is excellent.

 

[Craig Stocks]

I have had similar experience with the XF. Focus trim does seem to give different settings depending on distance and I always double tap (at least).

The XF is a fantastic platform with some wonderful and unique features geared for real photography, but autofocus is not one of its strengths. It's easy to evaluate accuracy while setting lens trim and the first and second taps are always a little different. In use I tend to just keep tapping autofocus until the lens stops hunting so usually at least 3 taps. Then I shoot a frame and check focus on the back or tethered laptop. In contrast when I shoot with my Canon or Sony I just focus once and shoot without ever worrying that it may have missed.

To be honest I'm not convinced that the XF autofocus is any better than the DF. In practice I still have to multi-tap focus and double check before continuing and I don't get any more frames in focus.

 

[Bill Caulfeild-Browne]

I have found the autofocus works just fine - see my pictures of Snow Geese with 240 where there was no time to double-tap.

As far as focus trim is concerned I find it best to focus on an object at infinity and take a series of shots at +10, -10 etc etc until I zero in on the perfect focus. (I have LensAlign but I've never had much luck with it.)

Of course, with Live View one can check static subjects easily.

 

[Paul2660]

I have had similar experience with the XF. Focus trim does seem to give different settings depending on distance and I always double tap (at least).

The XF is a fantastic platform with some wonderful and unique features geared for real photography, but autofocus is not one of its strengths. It's easy to evaluate accuracy while setting lens trim and the first and second taps are always a little different. In use I tend to just keep tapping autofocus until the lens stops hunting so usually at least 3 taps. Then I shoot a frame and check focus on the back or tethered laptop. In contrast when I shoot with my Canon or Sony I just focus once and shoot without ever worrying that it may have missed.

To be honest I'm not convinced that the XF autofocus is any better than the DF. In practice I still have to multi-tap focus and double check before continuing and I don't get any more frames in focus.

Hi Craig

I find it to be about the same as your findings unless I have a blue Ring lens on. Just own 1 the 35LS.

I have wondered if the issue might be not the XF but lack of precision in the older LS lenses AF motors and gearing. I have also wondered if this the same reason Phase one can't allow you to use AF when using the focus stacking tool to set the near and far points. Whenever I try this with AF when I set one the points usually the far the lens always seems still be fine tuned with the silver knobs. So there is a bit of slack that seems to come into play.


Paul C

 

[DrakeJ]

The behaviour I've seen when calibrating against a lenscal spyder chart is that it doesn't matter if it's blue ring or not. Same behaviour. So it's the XF that finds focus too fast when a subject is well lit and the focus throw is long.

Steve Hendrix sent me a mail where they go through how to focus trim a lens on the XF and they recommend pressing the focus button several times to make sure the XF has settled on the target. The way I usually do it is I set the lens to infinity or as close as the lens goes and then focus once.

To clarify, when I calibrate my lenses I am relatively close to the chart. I assume photographers shooting landscape does not really care how well the lenses focus close up.

 

[algrove]

CI recommends using a large chart from the Macbeth making sure to fill the focus area with the chart. Then focusing from about 6-8 feet. Ask them as they have a recommended way to trim focus.