Recently Phase One released a brand new Phase One Camera, the XF. It replaces the DF-645 and DF-645 + , which were actually Mamiya camera’s. The XF is engineered and build from the ground up and has many features, but most of all a newly developed focusing system based on a 1Mpixel focus sensor (Honeybee) .
See my video on this here:
Immediate after the release of the new camera critics were received on the Focusing System. Many were expecting multiple focus points, like on standard DSLR’s. Much to their dislikes, the XF has a single central focus point.
I can’t say that I agree with the critics, as I have been using the new XF and before the 645df+ body. Both have a single focus point, located in the center of the lens. So, allow me to put down some words in defense of Phase One.
There are several reasons why it is engineered the way it is, and like anything else it is a well considered balance between features and quality.
Focus must be fast, accurate and reliable.
All Mirror Reflex camera’s (DSLR’s and Phase One) focus either through phase or contrast method. It is measured on a special CCD (focus CCD) and mounted inside the camera body along the normal mirror down light path. After all light travels through the lens, hits the mirror, reflects in the prism and hits the eye on the viewfinder.
The Focus CCD provides the needed details on contrast to a compute engine which than drives the servomotor in the lens to increase or decrease the focal length. After each small step, the contrast is checked again. Until full focus is achieved.
Those DSLR’s with multiple selectable focus points (Nikon, Canon etc…) use only a part of the focus sensor. The focus sensor is partitioned and each partition matches to the selected focus area on the viewfinder. Hence only a sub set of the pixels (focus sensor) are used to track and hunt the focus.
A Phase One camera (single focus point) uses the full 1 Mpixel focus CCD to calculate and acquire focus. It makes it far more precise and accurate then any DSLR.
Furthermore, the Phase One XF uses a central focus point. This delivers the best and sharpest focus, as optical lenses are at best at their midpoint.
There is an usage disadvantage of having only a single center focus point , however that is by far outweighed by the superior focus .
Shooting with a single central focus point results in centric pictures. Not at all pleasing to look at, as we all appreciate the golden cut or 2/3 rules. Of course you could focus on the eyes of a model, and then lock the focus and reframe to a 2/3 kind of arrangement. That works well in most cases, however one can lose the focus especially with 1.4 or 2.8 lenses as they have a very shallow DOF.
With a multipoint focus system like the DSLR, it is easier to selected a single focus point at 2/3 of the picture frame and place it on the eye of the model. However the focus will not be that accurate as you are off-center and only a fraction of the Focus Sensor is used.
Never the less, the Phase One single focus point performs far better, and if you can’t get the swing of reframing without loosing the focus then shoot center stage. There is plenty of image pixel real-estate to crop in post processing (50,60, 80 and 100 Mpx image sensors).
The bottom line is, the Phase One XF central single focus point uses the full focusing sensor resulting in accurate and very fine adjustments , combined with the best optical performance of the lens ( center).
In the future, we might expect live-view methods. Whereby we will be able to tap on any area on the viewer display to acquire focus. That will be possible without the mirror box and Focus sensor. The image sensor will be used for both the Image Capture and Focus Sensing. Note that Phase One already has an electronic shutter capability.
Thanks for reading.