In the past, I've had some problems focusing correctly on aircraft approaches or aircraft take-offs.
Many times after I auto focus, the photo becomes out of focus because the plane is not fixed and is moving closer to me, thus a different setting of auto focus is need. So my photos are sometimes turning out soft as a result of this. I use an 80-320MM lens, and sometimes I have to adjust the zoom AFTER I focus, and as a result it will lose focus.
I use a Pentax ZX-7 which is acclaimed to have a very advanced auto focus system for an SLR of it's price range. It does have predictive autofocus according to the manual and Pentax's website. The manual says it automatically kicks in when it senses the object is moving.
Does anyone have any tips on how to keep the plane perfectly in focus throughout the entire phase of panning with it? It seems too tedious to constantly press the shutter button half way. Plus, that's a great way to drain out the batteries aswell.
Any help would be greatly appreciated.
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