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Using AF points

 
 
fishfry
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      02-09-2006
I have a Digital Rebel 350XT with 7 autofocus points. It does the right
thing in obvious situations, but gets hopelessly confused when shooting,
for example, a scenic shot with tree branches in the foreground. Slight
variations in composition cause it to change its mind about what to
focus on.

It seems to make more sense to just tell it to use only the center AF
point. Then focus-lock on whatever you want to focus on, recompose, and
shoot.

Can anyone explain the advantage of having it use all the AF points?
 
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Derek Fountain
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      02-09-2006
> I have a Digital Rebel 350XT with 7 autofocus points. It does the right
> thing in obvious situations, but gets hopelessly confused when shooting,
> for example, a scenic shot with tree branches in the foreground. Slight
> variations in composition cause it to change its mind about what to
> focus on.
>
> It seems to make more sense to just tell it to use only the center AF
> point. Then focus-lock on whatever you want to focus on, recompose, and
> shoot.


Agreed. I hardly ever use the full auto focus mode for the exact reasons
you state. In a simple scene the centre point, plus optional
recomposing, works fine. In complex scenes the auto system just gets
confused and forces me to shoot using the centre point anyway. So my 20D
stays with the centre point selected almost all the time.

> Can anyone explain the advantage of having it use all the AF points?


It can be useful when your subjects are moving and you don't have time
to recompose the shot, but it can still be fooled. Have a look at this
remarkable shot a friend of mine took:

http://www.esses.co.uk/tmp/wasp.jpg

An Aston Martin racer barrelling towards him at nearly 200mph, and the
camera finds a wasp to focus on. )

The auto focus technology is great, but whether it is really that useful
in a "serious" camera is more debatable.
 
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Malcolm Stewart
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      02-09-2006
"Derek Fountain" <(E-Mail Removed)> wrote in message
news:43eafec6$0$36849$(E-Mail Removed) reenews.net...
>
> It can be useful when your subjects are moving and you don't have time
> to recompose the shot, but it can still be fooled. Have a look at this
> remarkable shot a friend of mine took:
>
> http://www.esses.co.uk/tmp/wasp.jpg
>
> An Aston Martin racer barrelling towards him at nearly 200mph, and the
> camera finds a wasp to focus on. )


Interesting shot - assuming that the EXIF info hasn't been doctored and is
merely truncated, it was taken by a 10D, at the full resolution of 3072 x
2048 pixels. My 10D certainly doesn't have AF points that far from the
centre of the field.

--
M Stewart
Milton Keynes, UK




 
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John Fryatt
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      02-09-2006
fishfry wrote:
> I have a Digital Rebel 350XT with 7 autofocus points. It does the right
> thing in obvious situations, but gets hopelessly confused when shooting,
> for example, a scenic shot with tree branches in the foreground. Slight
> variations in composition cause it to change its mind about what to
> focus on.
>
> It seems to make more sense to just tell it to use only the center AF
> point. Then focus-lock on whatever you want to focus on, recompose, and
> shoot.


That's what I do. Seems more under my control than using multiple AF points.

> Can anyone explain the advantage of having it use all the AF points?


I'd be interested to hear opinions on this as well. Maybe it's just a
marketing thing that not many use in practice.

John
 
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Randy Berbaum
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      02-09-2006
John Fryatt <(E-Mail Removed)> wrote:

: I'd be interested to hear opinions on this as well. Maybe it's just a
: marketing thing that not many use in practice.

For those users or situations where full auto is useful or needed, having
some form of auto that takes all the photo training out of the process can
be good. Notice I also mentioned situations such as when conditions may
change very rapidly. But for most situations where at least minimal
composition and thought is possible, less auto is good. Having various
degrees of auto from "don't think" to "did you bring your scientific
calculator" is good. IMHO

Randy

==========
Randy Berbaum
Champaign, IL

 
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Tesco News
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      02-09-2006
"fishfry" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>I have a Digital Rebel 350XT with 7 autofocus points. It does the right
> thing in obvious situations, but gets hopelessly confused when shooting,
> for example, a scenic shot with tree branches in the foreground. Slight
> variations in composition cause it to change its mind about what to
> focus on.
>
> It seems to make more sense to just tell it to use only the center AF
> point. Then focus-lock on whatever you want to focus on, recompose, and
> shoot.
>
> Can anyone explain the advantage of having it use all the AF points?


Hi.

I believe there is some way that the Camera will set the aperture and the
focus, so that the furthest and nearest Focus Points wlll be withing the
Depth of Field. Assuming the lighting and ISO settings give it sufficient
depth.

How useful is that function?

About as good as the Nikon D70. When all Focus Points are activated, it
will focus on the closest one.

Roy G


 
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Steve Wolfe
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      02-09-2006
>I have a Digital Rebel 350XT with 7 autofocus points. It does the right
> thing in obvious situations, but gets hopelessly confused when shooting,
> for example, a scenic shot with tree branches in the foreground. Slight
> variations in composition cause it to change its mind about what to
> focus on.
>
> It seems to make more sense to just tell it to use only the center AF
> point. Then focus-lock on whatever you want to focus on, recompose, and
> shoot.
>
> Can anyone explain the advantage of having it use all the AF points?


If you're in AI-Servo, some of Canon's cameras can track a moving object
across the field of view, transferring from one AF point to another. I'm
not sure if the 350D can do that, or just the higher-end models.

steve


 
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Randall Ainsworth
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      02-09-2006
In article <(E-Mail Removed)>,
fishfry <(E-Mail Removed)> wrote:

> Can anyone explain the advantage of having it use all the AF points?


Great if you like our-of-focus pictures. Turn off all points except for
one.
 
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Bill Funk
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Posts: n/a
 
      02-09-2006
On Thu, 09 Feb 2006 08:34:07 +0000, Derek Fountain
<(E-Mail Removed)> wrote:

>> I have a Digital Rebel 350XT with 7 autofocus points. It does the right
>> thing in obvious situations, but gets hopelessly confused when shooting,
>> for example, a scenic shot with tree branches in the foreground. Slight
>> variations in composition cause it to change its mind about what to
>> focus on.
>>
>> It seems to make more sense to just tell it to use only the center AF
>> point. Then focus-lock on whatever you want to focus on, recompose, and
>> shoot.

>
>Agreed. I hardly ever use the full auto focus mode for the exact reasons
>you state. In a simple scene the centre point, plus optional
>recomposing, works fine. In complex scenes the auto system just gets
>confused and forces me to shoot using the centre point anyway. So my 20D
>stays with the centre point selected almost all the time.
>
>> Can anyone explain the advantage of having it use all the AF points?

>
>It can be useful when your subjects are moving and you don't have time
>to recompose the shot, but it can still be fooled. Have a look at this
>remarkable shot a friend of mine took:
>
>http://www.esses.co.uk/tmp/wasp.jpg
>
>An Aston Martin racer barrelling towards him at nearly 200mph, and the
>camera finds a wasp to focus on. )
>
>The auto focus technology is great, but whether it is really that useful
>in a "serious" camera is more debatable.


Interesting.
*Everything* but the wasp is equally blurred, inculding the track
nearest the wasp, and the camera doesn't have a focus point where the
wasp is. Is the shot cropped? No, it doesn't appear so; the URL of the
pic (http://www.esses.co.uk/tmp/wasp.jpg) shows the size of the
original is 3072x2048.
So, how was this really done?

--
Bill Funk
replace "g" with "a"
 
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Bill Funk
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Posts: n/a
 
      02-09-2006
On Thu, 09 Feb 2006 10:59:51 GMT, "Tesco News"
<(E-Mail Removed)> wrote:

>"fishfry" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>>I have a Digital Rebel 350XT with 7 autofocus points. It does the right
>> thing in obvious situations, but gets hopelessly confused when shooting,
>> for example, a scenic shot with tree branches in the foreground. Slight
>> variations in composition cause it to change its mind about what to
>> focus on.
>>
>> It seems to make more sense to just tell it to use only the center AF
>> point. Then focus-lock on whatever you want to focus on, recompose, and
>> shoot.
>>
>> Can anyone explain the advantage of having it use all the AF points?

>
>Hi.
>
>I believe there is some way that the Camera will set the aperture and the
>focus, so that the furthest and nearest Focus Points wlll be withing the
>Depth of Field. Assuming the lighting and ISO settings give it sufficient
>depth.


Yes, A-DEP, or Auto DEPth of field.
>
>How useful is that function?


It can be very useful. For groups of people where what's wanted is
everyone in focus, for example, it can work well.
>
>About as good as the Nikon D70. When all Focus Points are activated, it
>will focus on the closest one.
>
>Roy G
>


--
Bill Funk
replace "g" with "a"
 
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