A method of controlling a camera comprising: acquiring with a camera having a lens at a first focal length, a first image with a first field of view, said camera having an associated input camera projection model representing calibrated physical lens characteristics for acquiring an image including a focal length and an optical axis parameter value; displaying said first image with the current optical zoom of said first field of view; receiving a selection from a user of at least a portion of the first field of view to be displayed as a second image associated with an output camera projection model (40, 50, 60, 70), having a point of view in common with said input camera projection model and in which at least one of: a focal length and an optical axis parameter value, comprising one or both of pan or tilt, differ from the corresponding parameters of said input camera projection model, and immediately displaying said second image at the digital zoom corresponding to said portion of the first field of view; and iteratively: a) adjusting at least one of said focal length and an optical axis parameter value for said camera lens so that it approaches the corresponding focal length and optical axis parameter of said output camera projection model; b) acquiring a subsequent image with said camera using said adjusted focal length or optical axis parameter value; c) mapping pixel coordinates in said second image, using said output camera projection model, through a normalized 3-dimensional coordinate system to respective locations in said subsequent image, using said adjusted focal length or optical axis parameter values in said input camera projection model, to determine respective values for said pixel coordinates, thus providing a gradual improvement of the image sharpness as the digital zoom is replaced by the optical zoom; and d) redisplaying said second image with said determined pixel coordinate values wherein said steps a) to d) are repeated either: until said focal length and an optical axis parameter values for said camera lens match the corresponding value of said output camera projection model; or only to the point that all of the selected portion of the first field of view can remain visible in the displayed image. acquiring with a camera having a lens at a first focal length, a first image with a first field of view, said camera having an associated input camera projection model representing calibrated physical lens characteristics for acquiring an image including a focal length and an optical axis parameter value; displaying said first image with the current optical zoom of said first field of view; receiving a selection from a user of at least a portion of the first field of view to be displayed as a second image associated with an output camera projection model (40, 50, 60, 70), having a point of view in common with said input camera projection model and in which at least one of: a focal length and an optical axis parameter value, comprising one or both of pan or tilt, differ from the corresponding parameters of said input camera projection model, and immediately displaying said second image at the digital zoom corresponding to said portion of the first field of view; and iteratively: a) adjusting at least one of said focal length and an optical axis parameter value for said camera lens so that it approaches the corresponding focal length and optical axis parameter of said output camera projection model; b) acquiring a subsequent image with said camera using said adjusted focal length or optical axis parameter value; c) mapping pixel coordinates in said second image, using said output camera projection model, through a normalized 3-dimensional coordinate system to respective locations in said subsequent image, using said adjusted focal length or optical axis parameter values in said input camera projection model, to determine respective values for said pixel coordinates, thus providing a gradual improvement of the image sharpness as the digital zoom is replaced by the optical zoom; and d) redisplaying said second image with said determined pixel coordinate values wherein said steps a) to d) are repeated either: until said focal length and an optical axis parameter values for said camera lens match the corresponding value of said output camera projection model; or only to the point that all of the selected portion of the first field of view can remain visible in the displayed image. a) adjusting at least one of said focal length and an optical axis parameter value for said camera lens so that it approaches the corresponding focal length and optical axis parameter of said output camera projection model; b) acquiring a subsequent image with said camera using said adjusted focal length or optical axis parameter value; c) mapping pixel coordinates in said second image, using said output camera projection model, through a normalized 3-dimensional coordinate system to respective locations in said subsequent image, using said adjusted focal length or optical axis parameter values in said input camera projection model, to determine respective values for said pixel coordinates, thus providing a gradual improvement of the image sharpness as the digital zoom is replaced by the optical zoom; and d) redisplaying said second image with said determined pixel coordinate values until said focal length and an optical axis parameter values for said camera lens match the corresponding value of said output camera projection model; or only to the point that all of the selected portion of the first field of view can remain visible in the displayed image.