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Canon 20D Focus options



 
 
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  #1  
Old December 8th 04, 08:29 PM
N8urePix
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Default Canon 20D Focus options

Hello All,

I recently upgraded from a Canon 300D to a 20D and now have some options
available that I didn't have on the DRebel. One is the option of choosing
between three focus modes. One Shot AF, AI Focus AF and AI Servo AF. I have
read the manual until my eyes glazed over, trying to determine which of
these modes best suited my application. I use this camera for wildlife
photography only and shoot everything in AV mode. I use the center focus
point for AF on a still subject, such as a perched bird. If I want to photo
a bird in flight for instance, I change to automatic selection (all focus
points). I am wondering if one of the 3 AF options would be best suited for
both situations or do I need to be changing the AF mode as well as the focus
point? I am just not clear on the functionality of each of the three AF
choices. I am hoping someone in this group will have experience with them
and could offer some advice.

--
Bob

"Nature Photography by Bob Moul"
http://www.pbase.com/rcm1840


  #2  
Old December 8th 04, 09:06 PM
Bill Hilton
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Posts: n/a
Default

From: "N8urePix"

I recently upgraded from a Canon 300D to a 20D and now have some options
available that I didn't have on the DRebel. One is the option of choosing
between three focus modes. One Shot AF, AI Focus AF and AI Servo AF.


The Canons I own have only two modes, One Shot and AI Servo, so the answer
below references only those. Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what AI
Focus does, sorry ...

I use this camera for wildlife
photography only and shoot everything in AV mode. I use the center focus
point for AF on a still subject, such as a perched bird.


Either OS or AI will work for this type shot but OS has the advantage of
allowing you to lock the focus by pressing the shutter button half way and then
re-compose, keeping focus so long as you don't lift your finger from the
shutter button. AI will continue to change focus if you re-compose though. So
most people would use OS for still subjects and that's what Canon recommends.

If I want to photo a bird in flight for instance, I change to automatic
selection (all focus points).


Typically you'd use AI here since it will track the bird and keep it in focus
and this is especially useful if the bird is flying toward you or away from
you. If the bird is flying parallel then you can use OS and get sharp images
so long as the bird is still roughly parallel to you but most experts (and
Canon) recommend AI for moving objects.

I am wondering if one of the 3 AF options would be best suited for
both situations or do I need to be changing the AF mode as well as the focus
point?


I change modes often, the only problem with the bodies I have is that you can't
do it with one hand but other wise it's easy enough.

Bill


  #3  
Old December 8th 04, 09:06 PM
Bill Hilton
external usenet poster
 
Posts: n/a
Default

From: "N8urePix"

I recently upgraded from a Canon 300D to a 20D and now have some options
available that I didn't have on the DRebel. One is the option of choosing
between three focus modes. One Shot AF, AI Focus AF and AI Servo AF.


The Canons I own have only two modes, One Shot and AI Servo, so the answer
below references only those. Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what AI
Focus does, sorry ...

I use this camera for wildlife
photography only and shoot everything in AV mode. I use the center focus
point for AF on a still subject, such as a perched bird.


Either OS or AI will work for this type shot but OS has the advantage of
allowing you to lock the focus by pressing the shutter button half way and then
re-compose, keeping focus so long as you don't lift your finger from the
shutter button. AI will continue to change focus if you re-compose though. So
most people would use OS for still subjects and that's what Canon recommends.

If I want to photo a bird in flight for instance, I change to automatic
selection (all focus points).


Typically you'd use AI here since it will track the bird and keep it in focus
and this is especially useful if the bird is flying toward you or away from
you. If the bird is flying parallel then you can use OS and get sharp images
so long as the bird is still roughly parallel to you but most experts (and
Canon) recommend AI for moving objects.

I am wondering if one of the 3 AF options would be best suited for
both situations or do I need to be changing the AF mode as well as the focus
point?


I change modes often, the only problem with the bodies I have is that you can't
do it with one hand but other wise it's easy enough.

Bill


  #4  
Old December 8th 04, 09:17 PM
danielhphoto
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Default



The AI Focus is a mode between One Shot and Ai Servo.

Daniel



  #5  
Old December 8th 04, 09:17 PM
danielhphoto
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Default



The AI Focus is a mode between One Shot and Ai Servo.

Daniel



  #6  
Old December 9th 04, 04:23 AM
Bill Hilton
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Default

Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what AI
Focus does, sorry ...


I found this description of AI Focus on the net ...
"There is the usual One Shot as well as AI Servo tracking with predictive
autofocus. ... In addition there is AI Focus mode which locks focus in Single
Shot mode but then automatically switches to AI Servo with tracking if the
subject starts moving while the shutter release is partially depressed."

This sounds like a very useful mode to me (all I have is the technologically
deprived 1D Mark II and the ancient 1Ds so I don't have this mode
  #7  
Old December 9th 04, 04:23 AM
Bill Hilton
external usenet poster
 
Posts: n/a
Default

Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what AI
Focus does, sorry ...


I found this description of AI Focus on the net ...
"There is the usual One Shot as well as AI Servo tracking with predictive
autofocus. ... In addition there is AI Focus mode which locks focus in Single
Shot mode but then automatically switches to AI Servo with tracking if the
subject starts moving while the shutter release is partially depressed."

This sounds like a very useful mode to me (all I have is the technologically
deprived 1D Mark II and the ancient 1Ds so I don't have this mode
  #8  
Old December 9th 04, 05:27 AM
Roger N. Clark (change username to rnclark)
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Posts: n/a
Default

Bill Hilton wrote:
Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what AI
Focus does, sorry ...



I found this description of AI Focus on the net ...
"There is the usual One Shot as well as AI Servo tracking with predictive
autofocus. ... In addition there is AI Focus mode which locks focus in Single
Shot mode but then automatically switches to AI Servo with tracking if the
subject starts moving while the shutter release is partially depressed."

This sounds like a very useful mode to me (all I have is the technologically
deprived 1D Mark II and the ancient 1Ds so I don't have this mode


Bill,
On the 10D and D60 cameras, I never found the AI, or AI focus
were of much good for fast subjects, especially when unpredictable,
like birds at takeoff or landing. On the IDII, I've set the AI
to maximum rate and then it does real well (but my dogs playing are
still faster). Back to the 10D and D60: for fast action, I
learned to use single shot, and to lift my finger off the shutter
and then press it completely again. I got a higher number
of in focus shots. With AI or AI focus, I got a lot of
slightly out of focus images as the cameras always lagged behind.
Example, my Great Egret in Flight 1 image, at
http://www.clarkvision.com/features/...004/index.html
was done on a D60 in single shot mode.

So, I wonder if the 20D is more like the 10D or 1DII in its AI
tracking ability. So to Bob, if you find the birds out of focus
with AI, try single shot. Just remember to lift
your finger completely off the shutter button between shots.
I could frame at almost 3 per second with this method once
I learned it. Also, use only one sensor as with multiple sensors,
the camera can get confused and focus on the wrong thing
from what you want.

Roger

  #9  
Old December 9th 04, 05:27 AM
Roger N. Clark (change username to rnclark)
external usenet poster
 
Posts: n/a
Default

Bill Hilton wrote:
Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what AI
Focus does, sorry ...



I found this description of AI Focus on the net ...
"There is the usual One Shot as well as AI Servo tracking with predictive
autofocus. ... In addition there is AI Focus mode which locks focus in Single
Shot mode but then automatically switches to AI Servo with tracking if the
subject starts moving while the shutter release is partially depressed."

This sounds like a very useful mode to me (all I have is the technologically
deprived 1D Mark II and the ancient 1Ds so I don't have this mode


Bill,
On the 10D and D60 cameras, I never found the AI, or AI focus
were of much good for fast subjects, especially when unpredictable,
like birds at takeoff or landing. On the IDII, I've set the AI
to maximum rate and then it does real well (but my dogs playing are
still faster). Back to the 10D and D60: for fast action, I
learned to use single shot, and to lift my finger off the shutter
and then press it completely again. I got a higher number
of in focus shots. With AI or AI focus, I got a lot of
slightly out of focus images as the cameras always lagged behind.
Example, my Great Egret in Flight 1 image, at
http://www.clarkvision.com/features/...004/index.html
was done on a D60 in single shot mode.

So, I wonder if the 20D is more like the 10D or 1DII in its AI
tracking ability. So to Bob, if you find the birds out of focus
with AI, try single shot. Just remember to lift
your finger completely off the shutter button between shots.
I could frame at almost 3 per second with this method once
I learned it. Also, use only one sensor as with multiple sensors,
the camera can get confused and focus on the wrong thing
from what you want.

Roger

  #10  
Old December 9th 04, 01:50 PM
N8urePix
external usenet poster
 
Posts: n/a
Default

Bill, this is the mode I have been practicing with after reading the text in
the manual. I have not had much of an opportunity to try it on birds in
flight because of the weather, but I have tried focusing on objects like a
tree trunk, than while half depressing the shutter release, move the camera
to another object at a greater or lesser distance and the focus almost
instantly locks onto the latter. That is while using the center focus spot.
I agree with you, this seems to be the most versatile mode.

--
Bob

"Nature Photography by Bob Moul"
http://www.pbase.com/rcm1840
"Bill Hilton" wrote in message
...
Generally they recommend One Shot for stationary
subjects and AI for moving subjects since AI will track something and hold
focus while OS locks to one focus point and stops focussing. Dunno what
AI
Focus does, sorry ...


I found this description of AI Focus on the net ...
"There is the usual One Shot as well as AI Servo tracking with predictive
autofocus. ... In addition there is AI Focus mode which locks focus in
Single
Shot mode but then automatically switches to AI Servo with tracking if the
subject starts moving while the shutter release is partially depressed."

This sounds like a very useful mode to me (all I have is the
technologically
deprived 1D Mark II and the ancient 1Ds so I don't have this mode



 




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