AF points


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Octarine

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#2
No. Fast AF depends on the type of the sensor (cross-type vs. simple) and the processor behind to analyse and send the right signal to the lens. Lower end cams only have one cross-type sensor in the center, all the rest are just simple AF sensors). Higher end bodies have more than one cross-type sensor.
Multiple AF points help to track moving objects which might not be always in the center of the frame. Also, it helps to avoid the issue with "focus & recomposing" where the focal plain is very thin and slightest movements will result in OOF. Use the AF point that is across the part of the image that must be in focus (e.g. eyes). No need to shift the camera after focusing.
 

LBL2009

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#3
Thanks.

I can understand the part on moving object.

For off center subject, since there are many AF points cross the image, how do the camera decide which part of the body to focus on, if the camera take the average, then eye could be missed? Or I have to manually set the AF points?
 

Rashkae

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#4
Thanks.

I can understand the part on moving object.

For off center subject, since there are many AF points cross the image, how do the camera decide which part of the body to focus on, if the camera take the average, then eye could be missed? Or I have to manually set the AF points?
I suggest you try to read and research on Autofocus if that's really your interest. But the camera will normally focus on high-contrast areas. It can't automatically focus on the eyes for you, that's why you are supposed to manually select the AF point and then compose.
 

rendition

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#6
"19 cross-type for F2.8 or faster lens" - Can someone enlighten me what this mean... does it mean that the focus point is supposed to be somewhat faster and more accurate when 2.8 of faster lens is mounted on the body?

If so, strange that for the newer 1Ds3, it's f/2.8 or faster while 1Ds2 it's f/4 or faster - doesn't this mean the Mark 3 limits you more since you need faster glass...
 

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Rashkae

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#7
"19 cross-type for F2.8 or faster lens" - Can someone enlighten me what this mean... does it mean that the focus point is supposed to be somewhat faster and more accurate when 2.8 of faster lens is mounted on the body?
Exactly.

If so, strange that for the newer 1Ds3, it's f/2.8 or faster while 1Ds2 it's f/4 or faster - doesn't this mean the Mark 3 limits you more since you need faster glass...
Well, if you're shooting with a 1DsMkIII, you really should pair it with L glass to maximize the resolution.

But aside from that, it's not really limiting; in fact, it also indicated that the sensors are much more sensitive and accurate now.
 

flipfreak

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#9
"19 cross-type for F2.8 or faster lens" - Can someone enlighten me what this mean... does it mean that the focus point will be faster and more accurate when 2.8 of faster lens is mounted on the body?

If so, strange that for the newer 1Ds3, it's f/2.8 or faster while 1Ds2 it's f/4 or faster - doesn't this mean the 1Ds limit you more since you need fast glass...
the centre point for the 1D3 is cross sensitive when used with a f/4 or faster lens. the remaining 18 points becomes cross sensitive when used with a f/2.8 or faster lens.

meaning if you use a f/2.8 lens on the camera, all 19 points becomes cross sensitive. when used with a f/4 lens, the centre is cross while the rest are all horizontal types.

it is the same as the Mark II except the Mark IIs has the 7 cross type af points all clustered in the centre like the Nikons.

meaning on Mark II and III, if u use a f/4 lens, only the centre point is cross type.
 

hyori

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Mar 14, 2007
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#12
in fact im quite blur bout AF even after reading so much... for instant.. if i mf... and i select the point already... wad do u mean by re compose? very blur on focus
 

Rashkae

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#14
in fact im quite blur bout AF even after reading so much... for instant.. if i mf... and i select the point already... wad do u mean by re compose? very blur on focus
This is in your manual under the "Focus" section. Or google "focus and recompose"
 

hyori

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#15
I suggest you try to read and research on Autofocus if that's really your interest. But the camera will normally focus on high-contrast areas. It can't automatically focus on the eyes for you, that's why you are supposed to manually select the AF point and then compose.
Hi sorry can i query on this issue... when u say compose does it mean .. i select one AF point on the eye... den aeb lock it.. den focus again?
 

Rashkae

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Nov 28, 2005
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#16
Hi sorry can i query on this issue... when u say compose does it mean .. i select one AF point on the eye... den aeb lock it.. den focus again?
No. Please read your manual or google what I suggested in my previous post. COMPOSITION is different from FOCUS.

IF you have composed the picture and the selected AF point is already on the model's eye, great, just snap.

IF it is not, then prefocus on the eye using the closest AF point; you do this by half-pressing the shutter. Then, while it's half-pressed, you can recompose the image then fully depress once you're done.

This is in your manual, and in every basic newbie guide to photography. I suggest reading up a bit more.
 

limwhow

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Jun 9, 2009
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#17
Hi, gentlemen. I was following your discussions with keen interest. I use the 5dMkII.
I like to use the AF point on one side of the VF to focus on my subject, so that I do not need to recompose.
If I may OT slightly. My question is on metering: Personally I find that when use the side AF point and while on spot metering, I review the pictures and it seems that the camera meters on the centre of the VF, instead of on the AF point on the side.
Some CS members have said that the camera will only meter in centre of VF, but my camera shop people say that the spot metering will follow my AF points.
I am a little confused. Can you all advise me?
 

flipfreak

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#18
Hi, gentlemen. I was following your discussions with keen interest. I use the 5dMkII.
I like to use the AF point on one side of the VF to focus on my subject, so that I do not need to recompose.
If I may OT slightly. My question is on metering: Personally I find that when use the side AF point and while on spot metering, I review the pictures and it seems that the camera meters on the centre of the VF, instead of on the AF point on the side.
Some CS members have said that the camera will only meter in centre of VF, but my camera shop people say that the spot metering will follow my AF points.
I am a little confused. Can you all advise me?
it meters on the small circle in the centre. for canon, only the pro series has spot af on selected af point.
 

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