Argh!! Zoom-in focus zoom-out doesn't work?

Nimai

I can't believe I'm asking this, after literally tens of thousands of party photos, etc.

I started to suspect something the other night. I'm using the Canon 24-70mm, and I would zoom in a bit to make darn sure the center-focus I'm using is on the face of the subject. Then, focus-lock, frame, and shoot. When I frame it, I might zoom out a bit more.

Editing the photos today, a surprising number of faces are not in good focus! The focus appears to be a foot or more behind them.

Is this the result of a horrible habit? Can I not zoom in, focus, then zoom out to frame the photo?

angevin1

You must focus at the Zoom you will press the shutter button from. Even focusing and recomposing will change the focal plane of the subject-sensor, WITHOUT zooming in/out. of course these are two different scenarios and two different mechanical-light gathering reasons.

Nimai

Found this quote on another forum somewhere...

A parfocal lens is a zoom lens that stays in focus at the same point where you set it regardless of the focal length you zoom to. Ideally you focus at the longest FL (for best accuracy) and then zoom to the desired FL. AFAIK, all current Canon zoom lenses are not parfocal.

I guess I'll be changing my sequence of actions when shooting:
* Zoom/Frame
* Acquire focus by centering on desired spot and half-pressing
* Re-frame
* Shoot

angevin1

Nimai wrote: »

Found this quote on another forum somewhere...


I guess I'll be changing my sequence of actions when shooting:
* Zoom/Frame
* Acquire focus by centering on desired spot and half-pressing
* Re-frame
* Shoot

Actually reframing is one of the two scenarios I warned about. Reframing can easily change the focal plane/distance to the sensor and cause that DOF to go behind your subject.