1. Field of the Invention
The present invention relates to image pickup apparatuses capable of switching between an optical viewfinder and a live view mode.
2. Description of the Related Art
Many cameras having, besides a known optical viewfinder, an electronic viewfinder that obtains an image in an image pickup range using an image pickup device and displays the obtained image using a liquid crystal display monitor or the like (hereinafter referred to as a live view function or mode) have been proposed. Features of the live view function include strength against external darkness, that is, a reduction in luminance, ease of checking the depth of field, ease of performing special display such as enlargement, and the like.
Single-lens reflex cameras achieve focus using a phase-difference auto-focus (AF) method of achieving focus by separating light that has passed through an image pickup lens into components using a separator lens and obtaining the amount of lens movement based on the distance between images. Most of cameras of this type having the live view function use a contrast AF method of achieving focus based on contrast of image data obtained by an image pickup device.
In order to make use of features of the optical viewfinder and the live view mode, a single-lens reflex camera that switches between the optical viewfinder and the live view function has been proposed in Japanese Patent Laid-Open No. 5-107595.
When a camera can switch between the optical viewfinder and the live view mode, the camera performs the phase-difference AF method when using the optical viewfinder and performs the contrast AF method in the live view mode. The phase-difference AF method has an excellent focus speed. The contrast AF method has excellent focus precision. The two AF methods have respective features. There may be a situation where a user of the camera wants the camera to perform the phase-difference AF method even in the live view mode. To do so, a camera that can switch between the AF methods has been proposed in, for example, Japanese Patent Laid-Open No. 2001-272593.
Single-lens reflex cameras are often required to have a snap-shooting ability. Even when single-lens reflex cameras have the live view function, they may not use the contrast AF method, which requires a long time to achieve focus. In this case, focus in the live view mode is basically achieved with manual focus. Unlike a normal operation where AF is set by the first stroke of a release button and then an image is captured by the second stroke of the release button, an image can be captured without regard to a focus position. In such a case, when the phase-difference AF method is enabled by a user operation, the mode is changed to the optical viewfinder mode for a necessary period, an AF operation is performed using the phase-difference AF method, and then the mode is changed back to the live view mode.
However, in the phase-difference AF method using the optical viewfinder, some functions are in association with a photometric program using the optical viewfinder. These functions include an automatic depth-of-field priority AF function (hereinafter called “auto-depth”, which will be described in detail later) and an auto-exposure (AE) lock function that locks a photometric value when focus is achieved based on an evaluation photometry result at a focus ranging point. When the optical viewfinder and the live view function use different photometric methods, if the mode returns to the live view mode after an AF operation using the phase-difference AF method has been performed and photometry is performed with a photometric method in the live view mode, inconsistency may be caused.
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