Sharon
J. Norman Kern wrote:
> Perry wrote:
>
> > Several posters are getting in real deep with the XL-1 focus mechanism.
> > There seems to be some suggestion that lenses with an internal focus
> > mechanism cannot track whilst zooming - this is piffle!
> > My broadcast Canon 8 x 6 and many of its modern cousins and rivals often
> > use internal focus so that the lens front element is static and can
> > mount a filter holder.
> > Perry Mitchell
>
> Perry:
>
> All internal focus mechanisms are not the same. A professional zoom lens
> with internal focus still uses separate elements for focus control, just
> like a traditional zoom lens. The focus ring moves one or more elements just
> behind the front one. Those elements are entirely independent of the zoom
> section of the lens.
>
> The zoom lenses with the focus problem being discussed have NO elements,
> front mounted or otherwise, for exclusive focus control. They accomplish
> focus by changing the distance between two groups of zoom elements. They
> accomplish macro focus the same way.
>
> Your broadcast lens has macro focus too. Most of these do so by moving the
> prime lens element group at the extreme rear of lens, like adjusting back
> focus.
>
> You are fortunate to be using professional lenses, Perry, you're missing out
> on the 'fun' of tyring to use a lens that zooms in and out of focus. :-)
>
> --
> Norm Kern, President Kern Video Productions Inc.
> kvp@erinet.com Production/Editing/Distribution
> Check our website: Entertainment/Broadcast/Corporate
> http://www.erinet.com/kvp Special Interest/Personal/Duplication
> Betacam SP/ Hi-8/ S-VHS /DVCPRO /DVCAM
-- Sharon Stevenson Tel/fax (51-1) 444-4749 Lima, Peru ---------------------- Our best hope for civility? The Golden Rule: Treat others as you wish to be treated--for the good of us all! :-)