The traditional solution for most DSLRs has been to equip the camera with a multi-point AF sensor. These sensors allow the photographer to fix an off-center focus point on an off-center subject, which is then focused correctly. Such multi-point AF solutions are often tedious and inflexible to work with, however, and do not really solve the problem, claims Christian Poulsen.
Photographers have grown accustomed to using auto-focus systems in their day to day work and we see increasingly higher numbers of focus points advertised in each new wave of AF products. The term “multi-point auto-focus” is a bit misleading, however, for cameras with sensors larger than APS. Due to the physics of an SLR-camera, the off-center focus points that are offered are all clustered relatively close to the center of the image. To set focus outside of this center area, the photographer is still forced to focus first, and then shift the camera to reframe, with the resulting loss of focus as a result.
To overcome this problem, we have used modern yaw rate sensor technology to measure angular velocity in an innovative way. The result is the new Absolute Position Lock (APL) processor, which forms the foundation of our True Focus feature. The APL processor accurately logs camera movement during any re-composing, then uses these exact measurements to calculate the necessary focus adjustment, and issues the proper commands to the lens’s focus motor so it can compensate. The APL processor computes the advanced positional algorithms and carries out the required focus corrections at such rapid speed that no shutter lag occurs. The H4D’s firmware then further perfects the focus using the precise data retrieval system found on all HC/HCD lenses.
This technology takes AF to an entirely new level, correcting for the vertical and horizontal focus-shift that results from the rotation of the camera around an axis close to camera. In simple terms, True Focus allows the photographer to concentrate on their composition, to focus on their creativity, while True Focus takes care of the other, more mechanical focus.
True Focus on the H4D can be set to work at a half press of the camera release button, or via any user button programmed to AF-drive when the camera is in manual focus mode. This, the first release of True Focus, only corrects the horizontal and vertical positioning of the camera, and does not correct for any focus-shift which results from larger lateral movements of the camera during recomposing. The True Focus technology and APL (both patent pending) are the result of many years of development work and mark a significant milestone for Hasselblad’s high-end DSLR strategy and represent. We hope you use them well.
From Hasselblad – 29 Sept 2009
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