please explain 11 point focus' proper use?

[silverspear]

Hi seniors:

would basic questions be too "duhhh" here? I am a newbie transiting to DSLR, so really want to know some of the cool features that pros use.. thus need to ask, so i can learn =)

first up.. 11 point focus. this is a feature i dun see in P&S. Can someone explain to me how pros find this useful, compared to the normal way of pointing at object, focus, den shift the camera to recompose the shot?

=)

 

[darrrrrrrrrr]

Hi seniors:

would basic questions be too "duhhh" here? I am a newbie transiting to DSLR, so really want to know some of the cool features that pros use.. thus need to ask, so i can learn =)

first up.. 11 point focus. this is a feature i dun see in P&S. Can someone explain to me how pros find this useful, compared to the normal way of pointing at object, focus, den shift the camera to recompose the shot?

=)

at least you know how to focus then recompose :thumbsup:

with shallow DOF on a FA50 lens, for example, you will have so shallow DOF that the movement of recomposing might cause the subject to shift off the focus plane, so you pick the closest AF point to minimise that movement. also it prevents you from looking like a twitching monkey with all that pointing here and there.

if you are shooting sports on AF-C and you have a pre-visualised composition, you might want to pick an off-centre AF point and use that to track the subject rather than fiddling with configuring the AF/OK button to enable/disable AF so you can recompose.

if you are shooting landscapes on a tripod you could select a AF point to AF with rather than fiddling with the ballhead just to focus and then recompose the shot.

 

[flowerpot]

when u recompose, u hand will shift slightly, unless u can move like robot in parallel on the focus plane to the subject...:bsmilie:

11 point is there to help u focus when ur subject is off center, also using dslr, chances u might be using a fast lens which DOF can be thin and focus needs to be more spot on, recompose might missed...

pns usually dof not so critical as compare to dslr...

this is only true for dslr, but for film can some what tolerate the recompose method to a certain extent...

 

[woefulwabbit]

PnS don't have this feature, because with contrast detection you practically have infinite AF points (exaggeration.. you're limited by the megapixels and the number of pixels required to test for contrast).

I'm not sure how a pro will find all the AF points useful also, since I think most pros will just be using center point AF. The multiple AF points I thought help newbies that don't know how to point at object, focus, shift... when you set to auto AF point select. Sometimes I do select specific AF points when I use with tripod and remote control and want to stand somewhere other than the middle of the frame.

 

[darrrrrrrrrr]

PnS don't have this feature, because with contrast detection you practically have infinite AF points (exaggeration.. you're limited by the megapixels and the number of pixels required to test for contrast).

I'm not sure how a pro will find all the AF points useful also, since I think most pros will just be using center point AF. The multiple AF points I thought help newbies that don't know how to point at object, focus, shift... when you set to auto AF point select. Sometimes I do select specific AF points when I use with tripod and remote control and want to stand somewhere other than the middle of the frame.

no because P&S have face detection so the camera can choose the face, don't even need the operator to decide anything. :bsmilie:

 

[silverspear]

wow! darrrr, best explanaation! now i know how and when to use it =) i was like wondering the whole week why would anyone need 11 points of focus.. so troublesome :bsmilie: now i'm wiser just abit =)

 

[darrrrrrrrrr]

wow! darrrr, best explanaation! now i know how and when to use it =) i was like wondering the whole week why would anyone need 11 points of focus.. so troublesome :bsmilie: now i'm wiser just abit =)

some of the nikons have 51 points for continuous, predictive AF tracking across the frame, but i don't think most users need so many, but it's good to have if you ever need to shoot BIF i guess

anyway if my memory serves me right, the 3x3 grid are cross-type sensors so they can detect horizontal and vertical contrast, while the extreme left and right sensors are vertical line sensors (only can detect horizontal contrast). also, the AF sensor is apparently much bigger than the red-light indicator (which the k-x lacks anyway) so AF may not be so accurate and the camera could lock on something other than what you are aiming at, depending on which is more contrasty.

 

[banana0ne]

Panasonic Lumix PNS's have 9 point cross grid focusing but it only detects the nearest point to lock on but you don't have any option to shift the focus point manually.

 

[darrrrrrrrrr]

why you should set your AF point selection mode to AUTO before handing your cam off to someone else:

with them, the centre AF point is never used at all :bsmilie:

btw, IT IS SNOWING!

 

[Gengh]

why you should set your AF point selection mode to AUTO before handing your cam off to someone else:

with them, the centre AF point is never used at all :bsmilie:

btw, IT IS SNOWING!

I feel your pain.... but hey, Woohoo! Winter wonderland! :lovegrin: I'm jealous....

 

[woefulwabbit]

Nice and sharp trees

 

[night86mare]

why you should set your AF point selection mode to AUTO before handing your cam off to someone else:

with them, the centre AF point is never used at all :bsmilie:

btw, IT IS SNOWING!

i think the photographer is too busy appreciating the scene behind :bsmilie::bsmilie:

anyways, regarding threadstarter's question..

also, not every scene allows you to recompose, sometimes you want a shot that you have previsualised, and you wait for the right moment.. and don't have the leisure of happily center focus + recompose.

other than that, what darren has mentioned is very true, especially for the landscape case.

 

[deathstar]

Where should I focus to keep both subjects in focus?

why you should set your AF point selection mode to AUTO before handing your cam off to someone else:

with them, the centre AF point is never used at all :bsmilie:

btw, IT IS SNOWING!

 

[woefulwabbit]

Depends on your AF setting. If it is set to auto, then it should automatically pick out the two guys to focus on.
If set to center spot... then you have to aim the center point at one of the two guys, half press shutter to allow the focus to lock on the guy, then reframe the two guys as in the image and full press the shutter release.
If set to spot select.. then you probably don't know what you are doing

What happened in the picture is that the person behind the camera is using center spot (or spot select center) and just frame the shot as above and fully press the shutter release.. the camera then focus on the center spot which is the background behind and then fires away.

 

[CorneliusK]

Well since you are asking in the Pentax forum, this bit is relevant.

Note that the Pentax K-x does not show which point it is focusing on within the viewfinder, so even though it has an 11 point AF its somewhat useless since you cannot be sure what it is focusing on. You either have to use live view or use center point and recompose.

Something to note if you are considering the K-x!

(I still love it anyway!)

 

[woefulwabbit]

Yes as I've mentioned there are 3 modes:
Spot Center - Always use the center point
Spot Select - You can choose which of the 11 spots to use
Auto AF (5, 9 or 11) - Camera measures distance to all 11 (or 5 or 9) AF spots and decides which one to use through some algorithm.. from my tests it looks like it will ignore the points that are far away, and tries to find a point or combination of points that covers as many nearby points as possible.

 

[sid8888]

question regarding focussing: what if taking a group of people, set to auto 11pt as well?
how about if they are seated at a large round table such that each person is at a different distance to the camera?

 

[woefulwabbit]

question regarding focussing: what if taking a group of people, set to auto 11pt as well?
how about if they are seated at a large round table such that each person is at a different distance to the camera?

The nice thing about a round table (e.g. in weddings) is that everyone standing/sitting at one side to face the camera will naturally curve and remain somewhat equi-distance to the camera. It's not perfect, of course... and anyway you always want to focus on the couple

If it's just a general table shot and not people standing at one side, then you'll have to guess an 'in-the-middle' object to focus on with spot AF to try to get as many things in focus as possible. Or you can use auto-11 and hope the camera gets it right. Increase the DOF by stopping down the aperture, use wide angle, and use an external flash.