arthur_serino

<p>As an experienced user of these lenses, I can tell you everything you need to know about this amazing and underrated set of features!<br> The pushbutton and switch labeled P/A/AS on some lenses and PZ/AZ/MODE on others concern the auto-zoom functions. How they work depends on the camera body you have it attached to, and what firmware it has. <br> P or PZ means "power zoom", you control the zoom manually as with any other lens, except the motor does the work for you and all you have to do is turn the ring slightly. In this mode, the camera does not control the zoom motor at all, except to reduce the lens to its smallest physical size when you switch the camera off. This type of lens is significantly easier to use than a traditional zoom lens which requires more extensive manipulation of the controls, and any additional drain on the battery is insignificant. Zooming the lens electrically will also adjust your flash unit and keep the subject in focus without having to half-press the shutter release.<br> A or AZ means "auto zoom", and this is where having of a zoom motor really comes in handy. There are several modes of automatic zooming you can select:<br> The first auto-zoom mode works very much like the auto-focus on "servo"; it tracks your subject with the zoom and focus simultaneously, keeping it sized consistently in the frame. This is useful for tracking moving subjects such as players on an football field, cars on a racetrack, animals in their natural habitat, skiers, or anything that moves about quickly. Depending on the camera, the pushbutton may is used to focus and lock the subject's size in frame. <br> Another auto zoom mode is memory or "paper clip", where you can preset a focal length and then instantly recall it by pressing the button. On some cameras, you can preset two focal lengths and press the button to alternate rapidly between them. As you can imagine, this is a highly useful feature for action photography, as it allows you to snap back to your optimum focal length without even altering your grip! If I am using a hood or filter stack which causes vignetting at wide angles, I often use this feature to preset the shortest focal length I can get without vignetting.<br> The third and least common auto-zoom mode is the "zoom effect" or "zoom during exposure" mode. This is more of a specialist feature, but it does create interesting effects for fireworks and lighting displays. This feature must be used with a tripod, of course, and you'll probably want a cable release, but it takes all the hassle and guesswork out of this technique. After you set your desired exposure, the camera exposes half the time with the lens at whatever focal length you set, then zooms in quickly during the second half of the exposure, creating a radial effect. You can have the camera zoom out, instead. The motor makes this technique much easier, since there is no need to touch the camera, and the action of the motor is perfectly smooth. Not all the auto-zoom cameras can do this, but the best of them can.<br> I know of no firmware that allows the auto-zoom features to be used on any digital camera while shooting video, although that would be quite useful. The zoom motor in your lens will not work at all unless the camera has the two extra pins in the lens mount that provide power to the zoom motor. Some later models still have the pins, which are also used to provide power to lenses which have internal focusing motors.</p>