Al servo good or bad

[Cutter]

I am unsure on what Al servo does regarding focus. I know its for moving objects but If I used Alservo on a static object would the image be slightly out of focus? i dont think I have ever used it and got a sharp picture, i use the single point focus, should I be using multiipoint?

say the subject stopped for a while how would you be sure the eye was in focus there is no indication as to what your focused on ?

[Stormsong]

Cutter, this link may be useful:
http://www.shutterfreaks.com/Tips/CanonAIServo.html

There's also quite a technical discussion here:
http://forums.steves-digicams.com/ca...-ai-servo.html


Regards,
Denise

[Stormsong]

And also found this from my files:

http://www.ephotozine.com/forums/top...on-shots-87974

http://www.cambridgeincolour.com/tut...-autofocus.htm

Regards,
Denise

[Cutter]

Thanks Denise, great reads, so if i take a picture with Alservo and the subject is still then it wont be in focus, because its predicting a certain amount of movement that isnt there. Also for it to work well you have to be tracking your subject fo 1 to 2 seconds before firing.

Another hair do i owe you

[Cathus]

I wouldn't agree with your summary there Mark,

the auto focus should pick up a static object OK, it can only predict movement by watching the object moving & worlking out how far it moves so it can predict how far it will move in future, if it's not moving at all then there is no prediction to be made. If that makes sense.

The trouble with using autofocus on a static subject is that you can't focus & then recompose because if that subject is no longer under the focus point the camera will refocus on the new object under the focus.

Canon have a half way house between normal focus & AI focus where it focuses on an object & if the object doesn't move you can recompose & it will only refocus if it picks up movement, not sure if otjher cameras have the same - can't remember off top of head what they call it, I don't use it much.

The 1-2 second thing is really an 'in an ideal world' track for that, you'll find that in lots of circumstances you can track focus in a lot less time than that

[Cutter]

Originally Posted by Cathus

I wouldn't agree with your summary there Mark,

the auto focus should pick up a static object OK, it can only predict movement by watching the object moving & worlking out how far it moves so it can predict how far it will move in future, if it's not moving at all then there is no prediction to be made. If that makes sense.

The trouble with using autofocus on a static subject is that you can't focus & then recompose because if that subject is no longer under the focus point the camera will refocus on the new object under the focus.

Canon have a half way house between normal focus & AI focus where it focuses on an object & if the object doesn't move you can recompose & it will only refocus if it picks up movement, not sure if otjher cameras have the same - can't remember off top of head what they call it, I don't use it much.

The 1-2 second thing is really an 'in an ideal world' track for that, you'll find that in lots of circumstances you can track focus in a lot less time than that

Thanks Garry so what your saying is that if you have a static subject using Al servo should make no difference as long as the focus point is right ?

Just one more thing if i use a single shot focus on a walking subject with flash would it capture it in focus as long as the ss is fast enough ?

ps cameras coming next sat.

[Cathus]

yes, the continuous focus should lock on to anything static or moving.

the second point would depend on how fast the subject is moving & whether any movement would be covered by the depth of field available between the time you lock focus, press the shutter & the model moves (I presume this is re your model catwalk plans).

Depending on the ambient light exposure depends on whether the flash will freeze the action without motion blur but whether it's still in focus having used single shot may be a bit more hit & miss depending on the speed your lens/camera focuses at.

I'd utilise the kids or wife or friend to walk towards your camera & see whether you need continuous focus to get a good hit rate. Do it at dusk with the lighting levels you expect at the show & see whether the lens is accurate/fast enough to achieve fast focusing.

[Cutter]

Originally Posted by Cathus

yes, the continuous focus should lock on to anything static or moving.

the second point would depend on how fast the subject is moving & whether any movement would be covered by the depth of field available between the time you lock focus, press the shutter & the model moves (I presume this is re your model catwalk plans).

Depending on the ambient light exposure depends on whether the flash will freeze the action without motion blur but whether it's still in focus having used single shot may be a bit more hit & miss depending on the speed your lens/camera focuses at.

I'd utilise the kids or wife or friend to walk towards your camera & see whether you need continuous focus to get a good hit rate. Do it at dusk with the lighting levels you expect at the show & see whether the lens is accurate/fast enough to achieve fast focusing.

hey thanks for your advice garry, what iso can i go up to on the mk4 without showing too much noise ?

[Cathus]

I've not done any definitive tests, I regularly shoot 8000 ISO but then run stuff through Imagenomic Noiseware.

I have no concerns shooting ISO 1000-2000

On a general autofocus note, in my sports photography I shoot mostly in portrait mode, use continuous autofocus on one of the single focus points at the top of the screen & try to keep that on the face. I use this for players who are standing still also. The only time I put it back on single focus is if I want to do a portrait shot & recompose

[Cutter]

Originally Posted by Cathus

I've not done any definitive tests, I regularly shoot 8000 ISO but then run stuff through Imagenomic Noiseware.

I have no concerns shooting ISO 1000-2000

On a general autofocus note, in my sports photography I shoot mostly in portrait mode, use continuous autofocus on one of the single focus points at the top of the screen & try to keep that on the face. I use this for players who are standing still also. The only time I put it back on single focus is if I want to do a portrait shot & recompose

Thanks garry, why portrait mode, I have never used that ? as to the noise thanks for the info