Canon 70-200mm F2.8 With 1.4 Extender

Archived from groups: rec.photo.digital (More info?)

On 5/8/05 8:49 AM, in article laKdndZ65cJwhePfRVnyiw@pipex.net, "Russell"
<nospam@nospam.com> wrote:

> According to Canon's instructions:
>
> "If an extender (optional) is attached and the maximum aperture of the lens
> is f/5.6 or smaller, AF will not be possible. For details, see the
> Extender's instructions."
>
> Does that mean you loose Auto Focus when using a Canon 70-200mm F2.8 with
> 1.4 Extender? Or does AF work, but only from F8 and smaller (F5.6, plus the
> 1 stop loss from the converter).
>
> Anyone know why this is?
>
>
You are trying to make it too complicated! The lens always focuses at
maximum aperture, then stops down when the shutter button is pressed. So
the only thing that you need to be concerned about is the maximum aperture
available. The 1.4 extender will cost you one stop so your f2.8 lens will,
in effect, become an f4 lens. That is enough aperture for auto focus to
always work.
Chuck

Archived from groups: rec.photo.digital (More info?)

>"If an extender (optional) is attached and the maximum aperture of the

>lens is f/5.6 or smaller, AF will not be possible.

This is true for the consumer cameras, but with the Pro models like the
1Ds and 1D series it's f/8.

>Does that mean you loose Auto Focus when using a Canon 70-200mm
>F2.8 with 1.4 Extender?

No, because the "max aperture" is f/4 with this combo. You can also
use the 2x and the max aperture is f/5.6. It means you can't put the
1.4x on an f/5.6 lens and AF or the 2x on an f/4 lens and AF, that's
all.

>Or does AF work, but only from F8 and smaller ...

It will AF with the lens wide open and then stop down to the desired
aperture when you actually take the shot. So you can set it for f/32
but with the 1.4x or 2x t/c on the f/2.8 lens it will still AF, because
focussing takes place while the lens is wide open.

>Anyone know why this is?

Because the body needs a certain amount of light and contrast to
autofocus reliably.

Bill

Archived from groups: rec.photo.digital (More info?)

Cheers all.


"Russell" <nospam@nospam.com> wrote in message
news:laKdndZ65cJwhePfRVnyiw@pipex.net...
> According to Canon's instructions:
>
> "If an extender (optional) is attached and the maximum aperture of the
lens
> is f/5.6 or smaller, AF will not be possible. For details, see the
> Extender's instructions."
>
> Does that mean you loose Auto Focus when using a Canon 70-200mm F2.8 with
> 1.4 Extender? Or does AF work, but only from F8 and smaller (F5.6, plus
the
> 1 stop loss from the converter).
>
> Anyone know why this is?
>
>

Archived from groups: rec.photo.digital (More info?)

In message <427e611f$0$803$3a628fcd@textreader.nntp.hccnet.nl>,
"Marius" <nieuws*takeaway*@hrl.dosgg.nl> wrote:

>Fred Miranda gives a solution for the autofocus limitations of
>teleconverters:
>
>http://www.fredmiranda.com/TipsPage/

Of course, AF can become very slow and very inaccurate when forced to
work with a TC.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><