EOS f2.8 limit for AF-sensors

[WJM]

Haven't checked this specification for a long time, but with the
EOS-1(n), there was a limit of f2.8 for the AF-sensor, being
functional with both vertical and horizontal lines.
On the PhotoKina, the Canon guys looked at me as if they saw water
burning, when I mentioned this in the context of the new 70-200/4.0
IS....as if there never was such a limit, for more than one
generation....
Yet I don't even recall any big boasting of this limit being
nullified with any of the later EOS-1 series....
I do recall vaguely that the medium grade models suffered less from
this, but only by comprimising low-light performance....the center
sensor of the EOS-1 was much better in that context)


Willem
(still waiting for a 200mm/f2.8 IS, or even a 200mm/f1.8 IS
DO....just that the darn thing fits upright in my LowePro backpack,
like my 200/2.8 currently does, unlike all the IS-zooms in that
range)
Jan


--                
Bye,

Willem-Jan Markerink

      The desire to understand
is sometimes far less intelligent than
     the inability to understand

<w.j.markerink@...>
[note: 'a-one' & 'en-el'!]

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[Skip Middleton]

---- Willem-Jan Markerink <w.j.markerink@...> wrote:

> Haven't checked this specification for a long time, but with the
> EOS-1(n), there was a limit of f2.8 for the AF-sensor, being
> functional with both vertical and horizontal lines.
> On the PhotoKina, the Canon guys looked at me as if they saw water
> burning, when I mentioned this in the context of the new 70-200/4.0
> IS....as if there never was such a limit, for more than one
> generation....
> Yet I don't even recall any big boasting of this limit being
> nullified with any of the later EOS-1 series....
> I do recall vaguely that the medium grade models suffered less from
> this, but only by comprimising low-light performance....the center
> sensor of the EOS-1 was much better in that context)
>
>

IIRC, the EOS3, and subsequently, the 1v, had a lower limit of f8, but I don't know if that carried over to the digital versions.  As far as I know, all other models, Elan7, 30D, 5D, etc have that f2.8 limitation.
Skip Middleton
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[WJM]

On 4 Oct 2006 at 15:28, shadowcatcher@... wrote:

>
> ---- Willem-Jan Markerink <w.j.markerink@...> wrote:
> > Haven't checked this specification for a long time, but with the
> > EOS-1(n), there was a limit of f2.8 for the AF-sensor, being
> > functional with both vertical and horizontal lines. On the
> > PhotoKina, the Canon guys looked at me as if they saw water burning,
> > when I mentioned this in the context of the new 70-200/4.0 IS....as
> > if there never was such a limit, for more than one generation....
> > Yet I don't even recall any big boasting of this limit being
> > nullified with any of the later EOS-1 series.... I do recall vaguely
> > that the medium grade models suffered less from this, but only by
> > comprimising low-light performance....the center sensor of the EOS-1
> > was much better in that context)
> >
> >
> IIRC, the EOS3, and subsequently, the 1v, had a lower limit of f8, but
> I don't know if that carried over to the digital versions.  As far as
> I know, all other models, Elan7, 30D, 5D, etc have that f2.8
> limitation. Skip Middleton

Hmm, yes, but did this f8 limitation not apply to the outer/excenter
sensors only?
Including being much less light-sensitive, the cross-sensor still
beating them (and all the lower grade models)?


--                
Bye,

Willem-Jan Markerink

      The desire to understand
is sometimes far less intelligent than
     the inability to understand

<w.j.markerink@...>
[note: 'a-one' & 'en-el'!]

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[Tom Pfeiffer]

I think you're confusing the minimum aperture at which AF will work (f/8 on
the EOS 3 and 1 series bodies, f/5.6 on everything else), to the combination
(horizontal & vertical) central AF spot that enabled lenses of f/2.8 or
faster to focus using that AF point much faster/more accurately. AFAIK, the
limit still exists, but a quick Google search implies that it has been
improved to more sensors:

http://visual-vacations.com/Photography/canon_1_series_autofocus_custom_func
tions.htm

Some further scanning seems to imply that newer digital bodies like the 20D
have a hybrid center-point sensor that functions as a high precision sensor
with f/2.8 or faster lenses, as a normal precision sensor from f/4 to f/5.6,
and as a horizontal-line-only sensor for lenses slower than that.

> -----Original Message-----
> From: owner-eos@... [mailto:owner-eos@...] On Behalf Of
> shadowcatcher@...
> Sent: Wednesday, October 04, 2006 2:28 PM
> To: eos@...
> Cc: Willem-Jan Markerink
> Subject: Re: EOS f2.8 limit for AF-sensors
>
>
> ---- Willem-Jan Markerink <w.j.markerink@...> wrote:
> > Haven't checked this specification for a long time, but with the
> > EOS-1(n), there was a limit of f2.8 for the AF-sensor, being
> > functional with both vertical and horizontal lines.
> > On the PhotoKina, the Canon guys looked at me as if they saw water
> > burning, when I mentioned this in the context of the new 70-200/4.0
> > IS....as if there never was such a limit, for more than one
> > generation....
> > Yet I don't even recall any big boasting of this limit
> being nullified
> > with any of the later EOS-1 series....
> > I do recall vaguely that the medium grade models suffered less from
> > this, but only by comprimising low-light performance....the center
> > sensor of the EOS-1 was much better in that context)
> >
> >
> IIRC, the EOS3, and subsequently, the 1v, had a lower limit
> of f8, but I don't know if that carried over to the digital
> versions.  As far as I know, all other models, Elan7, 30D,
> 5D, etc have that f2.8 limitation.
> Skip Middleton
> *
> ****

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[Julian Loke]

>> WJM wrote
>> Haven't checked this specification for a long time, but with the
>> EOS-1(n), there was a limit of f2.8 for the AF-sensor, being
>> functional with both vertical and horizontal lines.

> Tom Pfeiffer wrote:
>
http://visual-vacations.com/Photography/canon_1_series_autofocus_custom_function
s.htm

Hi WJM,

This used to be a FAQ on this list sometime at the turn of the century.

For the 45-zone CMOS sensor, the limit was f/2.8 for the central group of 7
high-precision cross sensor; f/4 for the center cross sensor; f/5.6
for all remaining horizontal sensors except for the center, which remains
active to f/8.

See:
 http://eosdoc.com/manuals?q=AFCompat
 http://www.mail-archive.com/eos@.../msg02539.html
 http://tech.groups.yahoo.com/group/eos/message/39820

Cheers
Julian Loke


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[Skip Middleton]

----- Original Message -----
From: "Willem-Jan Markerink" <w.j.markerink@...>
To: <eos@...>
Sent: Wednesday, October 04, 2006 2:02 PM
Subject: Re: EOS f2.8 limit for AF-sensors

> On 4 Oct 2006 at 15:28, shadowcatcher@... wrote:
>
>>
>> ---- Willem-Jan Markerink <w.j.markerink@...> wrote:
>> > Haven't checked this specification for a long time, but with the
>> > EOS-1(n), there was a limit of f2.8 for the AF-sensor, being
>> > functional with both vertical and horizontal lines. On the
>> > PhotoKina, the Canon guys looked at me as if they saw water burning,
>> > when I mentioned this in the context of the new 70-200/4.0 IS....as
>> > if there never was such a limit, for more than one generation....
>> > Yet I don't even recall any big boasting of this limit being
>> > nullified with any of the later EOS-1 series.... I do recall vaguely
>> > that the medium grade models suffered less from this, but only by
>> > comprimising low-light performance....the center sensor of the EOS-1
>> > was much better in that context)
>> >
>> >
>> IIRC, the EOS3, and subsequently, the 1v, had a lower limit of f8, but
>> I don't know if that carried over to the digital versions.  As far as
>> I know, all other models, Elan7, 30D, 5D, etc have that f2.8
>> limitation. Skip Middleton
>
> Hmm, yes, but did this f8 limitation not apply to the outer/excenter
> sensors only?
> Including being much less light-sensitive, the cross-sensor still
> beating them (and all the lower grade models)?
>
>
> --
> Bye,
>
> Willem-Jan Markerink
>

Willem, I think you're looking at it upside down.  And that was compounded
by me not being clear in my own thinking.  The camera will AF at apertures
as small as f8 on the center sensor, but it requires f5.6 as a minimum for
AF.  F2.8 is required for cross sensors on the center for the lower line
models...
Skip Middleton
www.shadowcatcherimagery.com
www.pbase.com/skipm


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