AF-A, AF-C and AF-S

[qING]

Hi. I am usually using AF-A for my D40.

I was reading why 51 points was required (http://imaging.nikon.com/products/imaging/technology/d-technology/autofocus/02sensor/index.htm). And realised that there was AF-A, AF-S and AF-C.

I never changed the mode before and decided to give it a try after reading this article (http://www.slrphotographyguide.com/camera/nikon-digital-slr/focus-modes.shtml)

AF-S was no surprise. What shocked me was AF-C. If I half-pressed my focus on subject A and switched to subject B, the focus was changed to subject B in about 1-2 secs time. Both subjects were static.

Is this expected behaviour? Or am I doing it wrongly?

I suspected that this may be the reason why I sometimes the got wrong focus subject (AF-A chose AF-C instead of AF-S).

 

[ExplorerZ]

nothing wrong... if af-a choose af-s all the time, it wun be call af-a right? :dunno:

 

[qING]

nothing wrong... if af-a choose af-s all the time, it wun be call af-a right? :dunno:

Yeap.

Actually, what troubles me is AF-C.

If I focus on a moving object and the selected focus point is center, it seems that I cannot change my composition unless I change the focus point. Am I right?

But if a subject is moving, how can I change my composition without changing the focus point?

Changing focus point means moving from the center to the left or right. D40 only has 3 focus points.

 

[qING]

If I focus on a moving object and the selected focus point is center, it seems that I cannot change my composition unless I change the focus point. Am I right?

But if a subject is moving, how can I change my composition without changing the focus point?

Changing focus point means moving from the center to the left or right. D40 only has 3 focus points.

My conclusion came from the test stated in post 1.

If I half-pressed my focus on subject A and switched to subject B, the focus was changed to subject B in about 1-2 secs time. Both subjects were static.

 

[Jeremy1]

Although AF-C is for moving object, is there a difference using AF-C on static object as compare to using AF-S ?

 

[jeff7id]

Yeap.

Actually, what troubles me is AF-C.

If I focus on a moving object and the selected focus point is center, it seems that I cannot change my composition unless I change the focus point. Am I right?

But if a subject is moving, how can I change my composition without changing the focus point?

Changing focus point means moving from the center to the left or right. D40 only has 3 focus points.

Yes, the more focus points u have, AF-C would be more useful.
Such as 51 points AF for D300s or 39 points AF for D7000.
D40 is too limited on its 3 points AF.

That's why I use AF-S or MF more.

 

[ExplorerZ]

Yeap.

Actually, what troubles me is AF-C.

If I focus on a moving object and the selected focus point is center, it seems that I cannot change my composition unless I change the focus point. Am I right?

But if a subject is moving, how can I change my composition without changing the focus point?

Changing focus point means moving from the center to the left or right. D40 only has 3 focus points.

thats the limitation of lower end bodies, can't compare to higher end bodies like d300, d3 where they are more meant for sports and actions.
a good alternative is to zoom out a little and then crop it to ur liking later on.

Although AF-C is for moving object, is there a difference using AF-C on static object as compare to using AF-S ?

yes, only if u accidently shifted ur framing and end up focusing on something else instead.

 

[Jeremy1]

yes, only if u accidently shifted ur framing and end up focusing on something else instead.

Thanks a lot, at last someone answer my question.

Actually got quite a couple of doubts although I had played with my D700 for quite a while especially on the focusing side as some of my pictures are not sharp but some are sharp. :think:

 

[aungzawwin]

it was better to use AF-C in auto area AF(closest subject) when I used my D40

 

[kentwong81]

Do you know how to focus two subjects which are sitting far apart - one is far left and the other one is far right, and the rest subjects in the picture are blur?

 

[Jeremy1]

Hello, I would like to ask the following questions :

Is it to say that all will be in focus when you had manually adjusted the focus ring so that the camera indicator is indicating a circle for the D700 ?
If that is the case, your picture should be sharp ?

At what shutter speed should I set to freeze moving things example lion dance, people dancing/moving, leaves on tree & etc ? Does it got to do with focal length ?

Is there anyway to control what I want to focus. Example 2 different things wide apart as someone had mentioned ?

Thanks.

 

[aungzawwin]

Do you know how to focus two subjects which are sitting far apart - one is far left and the other one is far right, and the rest subjects in the picture are blur?

if i'd have time, i'd choose a spot which makes both persons in same focal plane, compose them properly, use tripod (and strobes if needed), select relatively large aperture, tell both of them not to move.. and smile, focus on a subject.. count 1,2,3, and fire

Hello, I would like to ask the following questions :

Is it to say that all will be in focus when you had manually adjusted the focus ring so that the camera indicator is indicating a circle for the D700 ?
If that is the case, your picture should be sharp ?

At what shutter speed should I set to freeze moving things example lion dance, people dancing/moving, leaves on tree & etc ? Does it got to do with focal length ?

Is there anyway to control what I want to focus. Example 2 different things wide apart as someone had mentioned ?

Thanks.

you mean "indicator/circle" the green dot in the view finder? it does not mean ALL subjects are in focus.. it only confirms the focus at certain AF point/points in use.. if nothing's wrong with your lens or other common factors (like handshake, subject movement after focus etc etc), it should be sharp of course..

1/125(plus flash if possible) should be enough to stop action, however it depends on how fast the subject is moving.. most of our DSLRs allow to use at least up to 1/4000
and yes, focal length is a factor to take into account.. the longer the FL, the faster the shutter speed needs to be (1/FL rule in general)..

generally speaking, i'd choose a distance at which those 2 things are placed relatively in a same focal plane so that focussing on one subject should also make the other in focus.. i'd also avoid very shallow DOF(large aperture) in such case.. shallow DOF can easily make things blur (a minor hand shake or subject movement for instance).. lenses are usually sharper if stopped down a stop or two from their maximum aperture..

i'm not accustomed to manual focussing.. as for a D90/D300s user, i'd try auto-area AF(menu set in 3D tracking mode) and AF-C.. the camera usually AF the subject.. spot on.. no brainer

 

[Jeremy1]

if i'd have time, i'd choose a spot which makes both persons in same focal plane, compose them properly, use tripod (and strobes if needed), select relatively large aperture, tell both of them not to move.. and smile, focus on a subject.. count 1,2,3, and fire



you mean "indicator/circle" the green dot in the view finder? it does not mean ALL subjects are in focus.. it only confirms the focus at certain AF point/points in use.. if nothing's wrong with your lens or other common factors (like handshake, subject movement after focus etc etc), it should be sharp of course..

1/125(plus flash if possible) should be enough to stop action, however it depends on how fast the subject is moving.. most of our DSLRs allow to use at least up to 1/4000
and yes, focal length is a factor to take into account.. the longer the FL, the faster the shutter speed needs to be (1/FL rule in general)..

generally speaking, i'd choose a distance at which those 2 things are placed relatively in a same focal plane so that focussing on one subject should also make the other in focus.. i'd also avoid very shallow DOF(large aperture) in such case.. shallow DOF can easily make things blur (a minor hand shake or subject movement for instance).. lenses are usually sharper if stopped down a stop or two from their maximum aperture..

i'm not accustomed to manual focussing.. as for a D90/D300s user, i'd try auto-area AF(menu set in 3D tracking mode) and AF-C.. the camera usually AF the subject.. spot on.. no brainer

Thanks for the answers.

So the circle only indicate certain focus point you have chosen base on the front lower switch ( Matrix, Centre & Spot focusing ).

 

[aungzawwin]

Thanks for the answers.

So the circle only indicate certain focus point you have chosen base on the front lower switch ( Matrix, Centre & Spot focusing ).

front lower switch is focus selector switch (AF-C, AF-S, MF)..

Matrix, Center, Spots are metering modes.. for D700, the selector is located near the right side of the view finder..

i'm afraid i was not discussing correctly about the "circle" you mentioned.. i was talking about the green AF confirmation dot (green circle) appeared in the view finder when the camera is in focus.. sorry if i'm wrong..

 

[virtuaoski]

Do you know how to focus two subjects which are sitting far apart - one is far left and the other one is far right, and the rest subjects in the picture are blur?

This is a typical focus-lock situation. First, you have to check if the two subjects are in the same focal plane (distance from you). If not, adjust your aperture to higher f-stop (small aperture) so that there is greater DOF.

Select "Spot AF" and the centre focusing point. Select AF-S or AF-A. Hold shutter half-way depressed on one of the two subjects until focussed, indicated by "beep-beep" / green AF confirmation dot. Keeping shutter half-depressed, re-compose picture and then depress shutter fully. Both subjects should be in focus. Hope this helps.

BTW, this technique works for any camera including PnS but you need to select Spot AF. I get frustrated when I borrow my friends' PnS and they have full-screen "closest subject" AF: it's just about impossible to tell the camera where to focus. Luckily, technology has brought "Face AF" to the rescue.