Digital BW, The Print

Here is a question that no one in my office can answer.
If you are taking a pic of someone 10 feet away, is focus maintained 
if you ZOOM-in to fine tune the focus and then ZOOM back out to take 
the pic? This is assuming the camera is in manual rather than 
autofocus mode.

that depends. technically focus should remain the
same, but only if you are using a true zoom lens. some
zooms are actually varifocal lenses and the focus will
be different at different focal lengths along the
lens' range. 

you could test this by zooming in, focusing, taking a
picture, and then zooming out and taking a picture. if
the subject stays in focus then your answer for that
lens is yes the focus is constant through the zsoom
range. this test would only be accurate-ish and only
if you used a wide aperture. so that depth of field
didn't cover focus error at the wider setting. 

if someone has technical numbers and such go ahead and
lay them out. 

--- digikdm <monroekd@...> wrote:
> Here is a question that no one in my office can
> answer.
> If you are taking a pic of someone 10 feet away, is
> focus maintained 
> if you ZOOM-in to fine tune the focus and then ZOOM
> back out to take 
> the pic? This is assuming the camera is in manual
> rather than 
> autofocus mode.
> 
> 


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