From: Wilba on
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. :- )


From: Paul Furman on
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
From: Wilba on
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. :- )


From: Paul Furman on
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

all google groups messages filtered due to spam
From: Wilba on
Paul Furman wrote:
> 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>.

Ah, OK. As long as it's not related to any known phenomenon of relevance, I
won't let it won't bother me. :- )

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

Yeah? We did that last night. <yawn> :- )