Whats crosstype autofocus points and how to use them?

So is it better to keep your focus point(s) in the middle to use the cross types?
In sports I normally use focusing dynamic 9 pushed off to the side. Does this affect it's ability of "better" focusing ?

As I understand it, yes...it would be 'better' to keep the focus points set to the middle area, in order to utilize the cross type sensors. However, if you have enough light and contrast that the outer points work fine....then it's probably not an issue worth worrying about.

It's in those time when you don't have as much light/contrast that there may be enough different to switch techniques.
 
The AF point indicators you see in the camera viewfinder only approximate the location of the AF point sensors.
Plus a single AF focus 'point' is actually a small array of sensors.

Except phase-detect AF done on the image sensor, the AF 'points' are actually part of the AF module in the bottom of the camera and are not located in the viewfinder.
 
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Focusing is always done before the lens stops down. So you are always focusing with the lens at it's maximum aperture. Therefore, a lens that has a larger maximum (F2.8), is getting more light (to focus with) than a lens with a maximum of F5.6.......even if you are shooting at F16 on both lenses.

That's interesting. The aperture blades must contract very fast when I press the button to take the photos. Thanks.
 
Focusing is always done before the lens stops down. So you are always focusing with the lens at it's maximum aperture. Therefore, a lens that has a larger maximum (F2.8), is getting more light (to focus with) than a lens with a maximum of F5.6.......even if you are shooting at F16 on both lenses.

That's interesting. The aperture blades must contract very fast when I press the button to take the photos. Thanks.
So if you are doing a burst at f/8 the lens system is actually ping-ponging between f/2.8 and f/8 between each shot ?

ahhh .. that's why the Depth-Of-Field review button is there.
 
The AF point indicators you see in the camera viewfinder only approximate the location of the AF point sensors. Plus a single AF focus 'point' is actually a small array of sensors.

Nikon said there are "39 point AF system with nine center cross type sensors".
If you say a point is actually a small array of sensors then must be less than 9 point auto focus point among these 39 AF points. In this case I would only trust only the center point has cross type censors.

I am very curious about this because I did have problems with getting tack sharp image even when I shoot portraits at my studio with decent light (modeling lights) and with my camera on tripod. Most are sharp but occasionally getting some blurry image when zoomed in. I used strobe and my model stands relative still, so I doubt it's the motion caused "blurry" image.
 
As I understand it, yes...it would be 'better' to keep the focus points set to the middle area, in order to utilize the cross type sensors. However, if you have enough light and contrast that the outer points work fine....then it's probably not an issue worth worrying about. It's in those time when you don't have as much light/contrast that there may be enough different to switch techniques.

Big mike, I just saw Nikon claims that D810 has cross type sensors works with lens of aperture F 5.5 or faster. So I guess different camera has different cross type sensor , some require large Max aperture and some require smaller max aperture like D810.
 
The AF point indicators you see in the camera viewfinder only approximate the location of the AF point sensors. Plus a single AF focus 'point' is actually a small array of sensors.

Nikon said there are "39 point AF system with nine center cross type sensors".
If you say a point is actually a small array of sensors then must be less than 9 point auto focus point among these 39 AF points. In this case I would only trust only the center point has cross type censors.

I am very curious about this because I did have problems with getting tack sharp image even when I shoot portraits at my studio with decent light (modeling lights) and with my camera on tripod. Most are sharp but occasionally getting some blurry image when zoomed in. I used strobe and my model stands relative still, so I doubt it's the motion caused "blurry" image.

It is possible the contrast is in between the AF points can cause the image slight blurry. The other AF points tend to focus on the contrast closer to the lens. Just like AF points select the subject you don't want. That is where center AF point comes in handy to select a specific subject.
 
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