Getting critical sharpness with Phase One's Autofocus Recompose feature

Posted on October 25, 2017

For a lot of people one of the biggest challenges they face working with digital medium format for the first time is focusing, particularly if they shoot handheld.

Often it involves a period of frustration as you have to recalibrate your skills to get the really high quality images you know are possible, but aren't quite nailing.

The recently released Autofocus Recompose mode (AFr) on the Phase One XF Camera does a lot to make focussing a breeze.


First though, why exactly can focussing be challenging?

Well partially it comes down to what you are used to. Certainly our customers who have come from shooting completely manual medium format systems think they are in heaven when they use the Phase One XF autofocus for the first time. In general though we are all so spoiled by DSLR and mirrorless systems with a bajillion autofocus points and eye tracking! If you are coming from a system like that it is obviously important to take the time to remember some good camera technique.

It also pays to keep in mind that due to the additional size of a full frame medium format sensor, depth of field is substantially narrower at equivalent apertures. So if you are shooting portraits on a Phase One at f/8, it is akin to shooting at f/4.5 on a DSLR.

Another aspect of focussing on medium format is that the higher resolution also highlights when focussing is out even a little bit, where at 24 megapixel the difference between perfectly sharp and almost perfectly sharp does not stick out as much.

Phase One BTS XF Studio FU4

So what is AFr mode?

As you are probably aware, whenever you focus on a point and then move to recompose your image the plane of focus will change, and likely what you focussed on is no longer in the plane. The typical example of this is focussing on your subject's eye using a centre focus point, then recomposing them for framing so their eyes are now toward the top of your image. What you find is their eyes have fallen forward of the plane of focus, with their ears being very very sharp - not ideal!

Phase One have updated the XF Camera with a new feature that uses the built in gyroscopes and accelerometers in the camera to measure and predict the movement you make between the moment you lock focus, and press the shutter.

In this way it is incredibly good at learning (yes learning!) your movement during a shoot and accounting for it... So that little bit of body sway you make as you breath in and out, as well as moving the camera to recompose are accounted for.

During use there is a fantastic audio feedback given by the camera: a chirpy positive sounding beep to reinforce to you when it has tracked your movement successfully, and a negative sounding one that tells you it has not.

Typically we have found on the very first shot you make it won't successfully track your movement, but after that it does. Don't ask us how but according to Phase One it "learns" your movement in each shot setup. The other time it gives you the negative beep is when you actually move so far that the original focus point is no longer in the frame or when your movement is too violent or inconsistent.

Hero Lenses Belluso 2600X950Px

There is additional benefits when using the XF with an IQ3 digital back; you can choose to have your preview automatically zoom in to the point of the image you were focussing on instead of the default centre point. With this option turned on you can quickly glance at the back and see within moments that you have nailed focus on a critical shot without breaking the flow of your shoot.

Compatibility

Currently AFr mode is available on all XF Cameras which have Feature Update 4 installed, and is compatible with several of the Blue Ring lenses.

See the range of Schneider Kreuznach Blue Ring lenses compatible with AFr below:

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