EF 50/1.8 AF Experiment?

OldBoy wrote:
Wilba wrote:
Wilba wrote:

Those results, and the fact that the lens is able to focus perfectly via
contrast detect, suggest to me that the "crude and sloppy mechanism"
theory is bogus. I suspect the truth is about the performance of the PD
AF sensor with this lens, specifically how much latitude it has for
confirming a focus. I noticed when manually focussing with a macro rail
that I could move the camera quite some (micro) distance and still get a
focus confirmation beep.

I've been thinking a lot about the width of the "beep band" and what it
means, so I measured it with a macro rail. With the lens at its closest
focus (430mm from the sensor), the far beep is 3.0mm from the near beep.
A conventional DOF calculation gives around 4.3mm, and a focus from the
nearside appears to put the subject bang in the middle of that. So that
means a farside focus would put the subject something like 0.8mm outside
the DOF, which sounds about right.

I also tried it at that distance with an EF-S 18-55 at about 50mm
(f/5.6). The beep band is 12mm, the DOF is 13mm, and where you start from
makes very little difference to the focus achieved (although from the
nearside is best again). I wish I had another wide-aperture FFL lens to
compare.

Any thoughts about why the 50/1.8 figures make sense (farside focus...
0.8mm outside the DOF), but it doesn't work like that for the 18-55?

Keep in mind that according to Canon, AF accuracy is within 1 CoC for
non-pro EOS camera's and within 1/3 CoC for pro EOS camera's.
(About +/- 0.02 mm resp. +/- 0.010mm at the sensor)

I thought that was about the high-precision AF sensor kicking in with lenses
that have a maximum aperture of f/2.8 or better...?

If it is about the max. aperture of the lens (and whether it's narrower than
f/2.8), then the 18-55 should perform worse, not better. Having thought some
more about this, I'm tending to think that it's probably more of a DOF thing
(harder to see it with deeper DOF) than the effect being absent with the
18-55.

"Wilba" wrote in message
...
OldBoy wrote:
Wilba wrote:
Wilba wrote:

Those results, and the fact that the lens is able to focus perfectly
via contrast detect, suggest to me that the "crude and sloppy
mechanism" theory is bogus. I suspect the truth is about the
performance of the PD AF sensor with this lens, specifically how much
latitude it has for confirming a focus. I noticed when manually
focussing with a macro rail that I could move the camera quite some
(micro) distance and still get a focus confirmation beep.

I've been thinking a lot about the width of the "beep band" and what it
means, so I measured it with a macro rail. With the lens at its closest
focus (430mm from the sensor), the far beep is 3.0mm from the near beep.
A conventional DOF calculation gives around 4.3mm, and a focus from the
nearside appears to put the subject bang in the middle of that. So that
means a farside focus would put the subject something like 0.8mm outside
the DOF, which sounds about right.

I also tried it at that distance with an EF-S 18-55 at about 50mm
(f/5.6). The beep band is 12mm, the DOF is 13mm, and where you start
from makes very little difference to the focus achieved (although from
the nearside is best again). I wish I had another wide-aperture FFL lens
to compare.

Any thoughts about why the 50/1.8 figures make sense (farside focus...
0.8mm outside the DOF), but it doesn't work like that for the 18-55?

Keep in mind that according to Canon, AF accuracy is within 1 CoC for
non-pro EOS camera's and within 1/3 CoC for pro EOS camera's.
(About +/- 0.02 mm resp. +/- 0.010mm at the sensor)

I thought that was about the high-precision AF sensor kicking in with
lenses that have a maximum aperture of f/2.8 or better...?

It's more a switch to higher sensitivity and by that more accuracy (no
hunting).

If it is about the max. aperture of the lens (and whether it's narrower
than f/2.8), then the 18-55 should perform worse, not better. Having
thought some more about this, I'm tending to think that it's probably more
of a DOF thing (harder to see it with deeper DOF) than the effect being
absent with the 18-55.

And in-lens stabilization helps also since the image on the AF sensor is
also stabilized :-)

Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:
Any thoughts about why the 50/1.8 figures make sense (farside focus...
0.8mm outside the DOF), but it doesn't work like that for the 18-55?
As others have said, the focal point will shift with f/number,
How is that a factor when shooting at widest apertures?
Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.
Yeah, this could still be the explanation. Which direction does the focus
shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away. For
example, if focus at f/1.4 is centered at 1.00 meters, then by f/2.8 it
might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is focusing
closer (when 'stopped down' through obstructions to the AF sensor),
then opening fully to the sensor for taking the pic; the actual point in
focus is further back. That's the opposite of what this effect would
suggest.

My version of this jigsaw puzzle has several significant pieces missing.
:- )

"Obstructions to the AF sensor" - what is that? How is that "stopped down"
(for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor for
taking the pic"? That sounds like something you'd say about the aperture,
but that isn't closing at any stage so it can't then open...?

Completely not getting what your saying. :- )

The view from the AF sensor isn't as clear as the view to the image
sensor so it's effectively stopped down a little. I'm not sure how exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior from
what you are getting.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

OldBoy wrote:
Wilba wrote:
OldBoy wrote:
Wilba wrote:
Wilba wrote:

Those results, and the fact that the lens is able to focus perfectly
via contrast detect, suggest to me that the "crude and sloppy
mechanism" theory is bogus. I suspect the truth is about the
performance of the PD AF sensor with this lens, specifically how much
latitude it has for confirming a focus. I noticed when manually
focussing with a macro rail that I could move the camera quite some
(micro) distance and still get a focus confirmation beep.

I've been thinking a lot about the width of the "beep band" and what it
means, so I measured it with a macro rail. With the lens at its closest
focus (430mm from the sensor), the far beep is 3.0mm from the near
beep. A conventional DOF calculation gives around 4.3mm, and a focus
from the nearside appears to put the subject bang in the middle of
that. So that means a farside focus would put the subject something
like 0.8mm outside the DOF, which sounds about right.

I also tried it at that distance with an EF-S 18-55 at about 50mm
(f/5.6). The beep band is 12mm, the DOF is 13mm, and where you start
from makes very little difference to the focus achieved (although from
the nearside is best again). I wish I had another wide-aperture FFL
lens to compare.

Any thoughts about why the 50/1.8 figures make sense (farside focus...
0.8mm outside the DOF), but it doesn't work like that for the 18-55?

Keep in mind that according to Canon, AF accuracy is within 1 CoC for
non-pro EOS camera's and within 1/3 CoC for pro EOS camera's.
(About +/- 0.02 mm resp. +/- 0.010mm at the sensor)

I thought that was about the high-precision AF sensor kicking in with
lenses that have a maximum aperture of f/2.8 or better...?

It's more a switch to higher sensitivity and by that more accuracy (no
hunting).

Yeah, by using a more accurate (i.e. wider "base") AF sensor than the f/5.6
sensor.

If it is about the max. aperture of the lens (and whether it's narrower
than f/2.8), then the 18-55 should perform worse, not better. Having
thought some more about this, I'm tending to think that it's probably
more of a DOF thing (harder to see it with deeper DOF) than the effect
being absent with the 18-55.

And in-lens stabilization helps also since the image on the AF sensor is
also stabilized :-)

Yeah, could do. I had it off for all the tests for that reason.

Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:

Any thoughts about why the 50/1.8 figures make sense (farside
focus... 0.8mm outside the DOF), but it doesn't work like that for
the 18-55?

As others have said, the focal point will shift with f/number,

How is that a factor when shooting at widest apertures?

Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.

Yeah, this could still be the explanation. Which direction does the
focus shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away. For
example, if focus at f/1.4 is centered at 1.00 meters, then by f/2.8 it
might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is focusing
closer (when 'stopped down' through obstructions to the AF sensor),
then opening fully to the sensor for taking the pic; the actual point in
focus is further back. That's the opposite of what this effect would
suggest.

My version of this jigsaw puzzle has several significant pieces missing.
:- )

"Obstructions to the AF sensor" - what is that? How is that "stopped
down" (for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor for
taking the pic"? That sounds like something you'd say about the aperture,
but that isn't closing at any stage so it can't then open...?

Completely not getting what your saying. :- )

The view from the AF sensor isn't as clear as the view to the image sensor
so it's effectively stopped down a little. I'm not sure how exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior from
what you are getting.

But how do you get aperture-related focus shift if you're not stopping down
for the exposure?

Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:
Any thoughts about why the 50/1.8 figures make sense (farside
focus... 0.8mm outside the DOF), but it doesn't work like that for
the 18-55?
As others have said, the focal point will shift with f/number,
How is that a factor when shooting at widest apertures?
Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.
Yeah, this could still be the explanation. Which direction does the
focus shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away. For
example, if focus at f/1.4 is centered at 1.00 meters, then by f/2.8 it
might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is focusing
closer (when 'stopped down' through obstructions to the AF sensor),
then opening fully to the sensor for taking the pic; the actual point in
focus is further back. That's the opposite of what this effect would
suggest.
My version of this jigsaw puzzle has several significant pieces missing.
:- )

"Obstructions to the AF sensor" - what is that? How is that "stopped
down" (for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor for
taking the pic"? That sounds like something you'd say about the aperture,
but that isn't closing at any stage so it can't then open...?

Completely not getting what your saying. :- )
The view from the AF sensor isn't as clear as the view to the image sensor
so it's effectively stopped down a little. I'm not sure how exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior from
what you are getting.

But how do you get aperture-related focus shift if you're not stopping down
for the exposure?

It would be opening up for the exposure. Like if you held a smaller
aperture over the front for focusing then removed it to take the shot.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:

Any thoughts about why the 50/1.8 figures make sense (farside
focus... 0.8mm outside the DOF), but it doesn't work like that for
the 18-55?

As others have said, the focal point will shift with f/number,

How is that a factor when shooting at widest apertures?

Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.

Yeah, this could still be the explanation. Which direction does the
focus shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away.
For example, if focus at f/1.4 is centered at 1.00 meters, then by
f/2.8 it might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is focusing
closer (when 'stopped down' through obstructions to the AF sensor),
then opening fully to the sensor for taking the pic; the actual point
in focus is further back. That's the opposite of what this effect
would suggest.

My version of this jigsaw puzzle has several significant pieces
missing. :- )

"Obstructions to the AF sensor" - what is that? How is that "stopped
down" (for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor for
taking the pic"? That sounds like something you'd say about the
aperture, but that isn't closing at any stage so it can't then open...?

Completely not getting what your saying. :- )

The view from the AF sensor isn't as clear as the view to the image
sensor so it's effectively stopped down a little. I'm not sure how
exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior from
what you are getting.

But how do you get aperture-related focus shift if you're not stopping
down for the exposure?

It would be opening up for the exposure. Like if you held a smaller
aperture over the front for focusing then removed it to take the shot.

What the flipping heck are you talking about!?! :- )

How can the aperture go wider than its widest?! Why/how/who/when would you
hold a smaller aperture over the front for focussing?

Are we actually talking about the same thing? The only aperture-related
focus shift I know about is like this -
http://diglloyd.com/diglloyd/free/FocusShift/index.html. What you're saying
only sounds like it might make some kind of sense in relation to something
completely different. :- )

Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:

Any thoughts about why the 50/1.8 figures make sense (farside
focus... 0.8mm outside the DOF), but it doesn't work like that for
the 18-55?
As others have said, the focal point will shift with f/number,
How is that a factor when shooting at widest apertures?
Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.
Yeah, this could still be the explanation. Which direction does the
focus shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away.
For example, if focus at f/1.4 is centered at 1.00 meters, then by
f/2.8 it might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is focusing
closer (when 'stopped down' through obstructions to the AF sensor),
then opening fully to the sensor for taking the pic; the actual point
in focus is further back. That's the opposite of what this effect
would suggest.
My version of this jigsaw puzzle has several significant pieces
missing. :- )

"Obstructions to the AF sensor" - what is that? How is that "stopped
down" (for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor for
taking the pic"? That sounds like something you'd say about the
aperture, but that isn't closing at any stage so it can't then open...?

Completely not getting what your saying. :- )
The view from the AF sensor isn't as clear as the view to the image
sensor so it's effectively stopped down a little. I'm not sure how
exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior from
what you are getting.
But how do you get aperture-related focus shift if you're not stopping
down for the exposure?
It would be opening up for the exposure. Like if you held a smaller
aperture over the front for focusing then removed it to take the shot.

What the flipping heck are you talking about!?! :- )

How can the aperture go wider than its widest?! Why/how/who/when would you
hold a smaller aperture over the front for focussing?

Are we actually talking about the same thing? The only aperture-related
focus shift I know about is like this -
http://diglloyd.com/diglloyd/free/FocusShift/index.html. What you're saying
only sounds like it might make some kind of sense in relation to something
completely different. :- )

:-)

The AF sensors are off to the side, looking through mirrors and/or
prisms or something, like the viewfinder. When you block part of their
view, the obstruction acts the same as aperture blades: making the
opening narrower.

When the actual photo is taken, all the mirrors get out of the way and
the full f/1.8 projects in all it's glory onto the photo sensor.

I could be wrong but that's my understanding.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:

Any thoughts about why the 50/1.8 figures make sense (farside
focus... 0.8mm outside the DOF), but it doesn't work like that
for the 18-55?

As others have said, the focal point will shift with f/number,

How is that a factor when shooting at widest apertures?

Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.

Yeah, this could still be the explanation. Which direction does the
focus shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away.
For example, if focus at f/1.4 is centered at 1.00 meters, then by
f/2.8 it might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is
focusing closer (when 'stopped down' through obstructions to the AF
sensor),
then opening fully to the sensor for taking the pic; the actual
point in focus is further back. That's the opposite of what this
effect would suggest.

My version of this jigsaw puzzle has several significant pieces
missing. :- )

"Obstructions to the AF sensor" - what is that? How is that "stopped
down" (for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor
for taking the pic"? That sounds like something you'd say about the
aperture, but that isn't closing at any stage so it can't then
open...?

Completely not getting what your saying. :- )

The view from the AF sensor isn't as clear as the view to the image
sensor so it's effectively stopped down a little. I'm not sure how
exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior
from what you are getting.

But how do you get aperture-related focus shift if you're not stopping
down for the exposure?

It would be opening up for the exposure. Like if you held a smaller
aperture over the front for focusing then removed it to take the shot.

What the flipping heck are you talking about!?! :- )

How can the aperture go wider than its widest?! Why/how/who/when
would you hold a smaller aperture over the front for focussing?

Are we actually talking about the same thing? The only aperture-related
focus shift I know about is like this -
http://diglloyd.com/diglloyd/free/FocusShift/index.html. What you're
saying only sounds like it might make some kind of sense in relation to
something completely different. :- )

:-)

The AF sensors are off to the side, looking through mirrors and/or prisms
or something, like the viewfinder.

Ri-ight.

When you block part of their view, the obstruction acts the same as
aperture blades: making the opening narrower.

What does that?! How's it relevant to _anything_ FFS? :- )

When the actual photo is taken, all the mirrors get out of the way and the
full f/1.8 projects in all it's glory onto the photo sensor.

Yeah... so at that point there's no light from the optical path falling on
the AF sensor. Why does it matter what the AF sensor is doing then?!! :- )

Just give me any clue, anything, about what this has to do with my
experiements and this kind of focus shift -
http://diglloyd.com/diglloyd/free/FocusShift/index.html - that _could_ be a
factor, _if_ I was stopping down the aperture from its maximum. :- )

Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Wilba wrote:
Paul Furman wrote:
Chris Malcolm wrote:
Wilba wrote:
David J Taylor wrote:
Wilba wrote:

Any thoughts about why the 50/1.8 figures make sense (farside
focus... 0.8mm outside the DOF), but it doesn't work like that
for the 18-55?
As others have said, the focal point will shift with f/number,
How is that a factor when shooting at widest apertures?
Because with a specific lens and AF sensor the focusing takes place
always at the effective aperture of the AF sensor, whereas the
aperture with which the photograph is taken can vary. Many cameras
have a max AF sensor aperture of around f6. Some go down as far as
f2.8. Hence if you're using a lens at f1.8, and it happens to be a
spherical lens design with aperture related focus drift (as many of
the golden oldie 50mms are), then this is an important factor.
Yeah, this could still be the explanation. Which direction does the
focus shift when stopping down? -that would provide a clue.
http://diglloyd.com/diglloyd/free/FocusShift/index.html
"With every lens I’ve tested to date, the focus moves farther away.
For example, if focus at f/1.4 is centered at 1.00 meters, then by
f/2.8 it might now be centered at 1.02 meters."

On average (ignoring front/back approach), Wilba's camera is
focusing closer (when 'stopped down' through obstructions to the AF
sensor),
then opening fully to the sensor for taking the pic; the actual
point in focus is further back. That's the opposite of what this
effect would suggest.
My version of this jigsaw puzzle has several significant pieces
missing. :- )

"Obstructions to the AF sensor" - what is that? How is that "stopped
down" (for the AF sensor?)?

What part of the camera+lens system is "opening fully to the sensor
for taking the pic"? That sounds like something you'd say about the
aperture, but that isn't closing at any stage so it can't then
open...?

Completely not getting what your saying. :- )
The view from the AF sensor isn't as clear as the view to the image
sensor so it's effectively stopped down a little. I'm not sure how
exactly.

The view on the ground glass is also. Supposedly anything faster than
perhaps f/2.8 doesn't improve the brightness, etc.

But this focus shift theory seems to predict the opposite behavior
from what you are getting.
But how do you get aperture-related focus shift if you're not stopping
down for the exposure?
It would be opening up for the exposure. Like if you held a smaller
aperture over the front for focusing then removed it to take the shot.
What the flipping heck are you talking about!?! :- )

How can the aperture go wider than its widest?! Why/how/who/when
would you hold a smaller aperture over the front for focussing?

Are we actually talking about the same thing? The only aperture-related
focus shift I know about is like this -
http://diglloyd.com/diglloyd/free/FocusShift/index.html. What you're
saying only sounds like it might make some kind of sense in relation to
something completely different. :- )
:-)

The AF sensors are off to the side, looking through mirrors and/or prisms
or something, like the viewfinder.

Ri-ight.

When you block part of their view, the obstruction acts the same as
aperture blades: making the opening narrower.

What does that?! How's it relevant to _anything_ FFS? :- )

When the actual photo is taken, all the mirrors get out of the way and the
full f/1.8 projects in all it's glory onto the photo sensor.

Yeah... so at that point there's no light from the optical path falling on
the AF sensor. Why does it matter what the AF sensor is doing then?!! :- )

Just give me any clue, anything, about what this has to do with my
experiements and this kind of focus shift -
http://diglloyd.com/diglloyd/free/FocusShift/index.html - that _could_ be a
factor, _if_ I was stopping down the aperture from its maximum. :- )

The trend this suggests is the opposite of what you are experiencing if
I'm following this right, so consider this a tangent. But if it were a
factor, it would be because there is something blocking the view that
the AF sensors see, so they are locking onto the target based on a
stopped down view.

It's like the AF sensor(s) are sitting at the side of the stage, peering
through the curtains at an angle through a small mirror g.

Happy New Year (my time) in one minute...

--
Paul Furman
www.edgehill.net
www.baynatives.com

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