Multiple AF points, what advantage?

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Duncan.F

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Duncan
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A bit puzzled about the relative value! Clearly you need an accurate and quick AF to pick up the subject but why have lots of af points. A lot of photographers seem to advocate using the centre one only, why would you then use all/some or even select an off centre one?

Cheers,

Dunc
 
I would imagine mainly for landscape and the like.(y)
 
Off centre I can understand to get composition right in-camera, all focus points for landscape I'd guess, but I am guilty of using only (and I mean only) using centre focus then cropping to get good composition (that is unless the subject is still in which case I'll manual focus).
 
DTM said:
Off centre I can understand to get composition right in-camera, all focus points for landscape I'd guess, but I am guilty of using only (and I mean only) using centre focus then cropping to get good composition (that is unless the subject is still in which case I'll manual focus).
Click to expand...

Instead of croping use the center focus point to focus then recompose before taking the shot - multiple focus points can be used when trying to track a moving object
 
I use off centre focus points a lot. If you are shooting a person you are unlikely to have the eyes in the centre of the frame. Now, you can focus on the eyes and recompose with the shutter half depressed to lock the focal point but that means moving the camera. That movement CAN (if you are not really careful with it) introduce camera shake into your shot.

The ideal is to simply shift the focus point so it lines up with the eyes in your composition and then you don't have to move the camera much, if at all.

Using this technique increased my keeper rate shooting in low light because I can get far more stable.
 
I use the focus point selection quite a lot. After exposure/aperture, I then frame up the shot and then select the focus point which I want. This lets me see the exact frame that I want with the confidence to know that the point that I want to get into focus will be as I want. I am sure the same is the case for Nikon etc. but my Canon controls for this have now come quite second nature to me and this can be done without taking the camera away from my eye - also when using the addition grip.
A Wedding Tog friend of mine also uses this feature extensively.
 
There is an article about this in this months photoplus magazine.
Diagnoal AF point is suggested for single person facial portraits, upper for landscapes, auto select for a shot with two people, edge for a moving object (depending if it's on the left or right) and centre for dull or bright objects.

I'm going to have a try with these as I find that with autoselect, not all of a landscape comes out in focus in some photos.
 
Thanks for the replies, what made me ask the question was the 'debate' about the AF system on the new 7D. THinking of getting one but have to save up....

Cheers,

Dunc
 
AliB said:
I use off centre focus points a lot. If you are shooting a person you are unlikely to have the eyes in the centre of the frame. Now, you can focus on the eyes and recompose with the shutter half depressed to lock the focal point but that means moving the camera. That movement CAN (if you are not really careful with it) introduce camera shake into your shot.

The ideal is to simply shift the focus point so it lines up with the eyes in your composition and then you don't have to move the camera much, if at all.

Using this technique increased my keeper rate shooting in low light because I can get far more stable.
Click to expand...

same here...makes a huge difference (y)
 
There I was trying to be constructive and now I ifnd that you are thinking about getting a 7D - I now hate you!, not really.
Enjoy it when you get it.
 
To ensure that the part of the scene you want is in focus, you need to use the nearest AF point. If you have to focus lock and recompose, you can introduce focussing errors. Having more points ensures you have to move the camera less = more in focus pictures!
 
Well I think the advantages for composition have been covered.

The thing about the 7D is that it's the first camera ever from Canon which enables you to gain focus lock on a moving subject with any of the 19 AF points. After focus lock is obtained, the system will pass focus from one AF point to another to keep focus lock as the positoion of the subject changes within the pattern of AF points, so it's a major improvement if it lives up to it's promise and should be a boon for bird in flight shots where movement can be erratic.

All previous Canon cameras - even 1 Series with 45 AF points, require you to first obtain focus lock with the centre AF point before it will pass focus to other AF points.
 
Cheng said:
To ensure that the part of the scene you want is in focus, you need to use the nearest AF point. If you have to focus lock and recompose, you can introduce focussing errors. Having more points ensures you have to move the camera less = more in focus pictures!
Click to expand...

This true for shooting big apertures when trying to isolate a subject but not for small aperture , small focal length landscape shots where the DOF is that big you'd struggle to see any difference.
 
Cheng said:
To ensure that the part of the scene you want is in focus, you need to use the nearest AF point. If you have to focus lock and recompose, you can introduce focussing errors. Having more points ensures you have to move the camera less = more in focus pictures!
Click to expand...

this is puzzling...how does one get a lens to focus on different points...during exposure:shake:
 
Now I didn't know that! Another tick in the box and and negative on the credit card!

Dunc

CT said:
Well I think the advantages for composition have been covered.

The thing about the 7D is that it's the first camera ever from Canon which enables you to gain focus lock on a moving subject with any of the 19 AF points. After focus lock is obtained, the system will pass focus from one AF point to another to keep focus lock as the positoion of the subject changes within the pattern of AF points, so it's a major improvement if it lives up to it's promise and should be a boon for bird in flight shots where movement can be erratic.

All previous Canon cameras - even 1 Series with 45 AF points, require you to first obtain focus lock with the centre AF point before it will pass focus to other AF points.
Click to expand...
 
I must admit I find dialing the focus points around a bit of a pain. I was brought up with that central focus ring where you got the two halves to align, and I tend to get the central one in focus and then recompose the shot, as we did then with manual focus.

I've only recently noticed people on here talking about the multiple focus points being used when tracking a subject. Could somebody explain how that works? I don't mean how does the camera achieve it but what is happening when you choose multiple points?
 
mrcrow said:
this is puzzling...how does one get a lens to focus on different points...during exposure:shake:
Click to expand...

Sorry, I don't understand your question. To clarify, more AF points allow you to compose then focus, rather than focussing then recomposing.
 
trapper501 said:
I must admit I find dialing the focus points around a bit of a pain. I was brought up with that central focus ring where you got the two halves to align, and I tend to get the central one in focus and then recompose the shot, as we did then with manual focus.

I've only recently noticed people on here talking about the multiple focus points being used when tracking a subject. Could somebody explain how that works? I don't mean how does the camera achieve it but what is happening when you choose multiple points?
Click to expand...

Usually what happens is you choose one point to 'acquire' focus i.e. the subject the camera is following. Then if the subjects moves from this initial point to any of the other AF points involved in focussing, they will track them too.
 
Cheng said:
Usually what happens is you choose one point to 'acquire' focus i.e. the subject the camera is following. Then if the subjects moves from this initial point to any of the other AF points involved in focussing, they will track them too.
Click to expand...

So you set it to multiple points, point camera at subject and half pressure shutter button.

When I do that I find it terrible frustrating that the damn thing doesn't get the subject and I need to make several attempts.

Are you saying that's worth it if the subject is/might move because one of the others will automatically pick it up?
 
trapper501 said:
So you set it to multiple points, point camera at subject and half pressure shutter button.

When I do that I find it terrible frustrating that the damn thing doesn't get the subject and I need to make several attempts.

Are you saying that's worth it if the subject is/might move because one of the others will automatically pick it up?
Click to expand...

If set to continuous focus - called AF-C on Nikon cameras - I think it's called continuous servo or something to that effect on Canons - and also activate multiple points - called dynamic focus for Nikons - then when you activate AF - i.e. half pressing the shutter, the subject will track. So worth it for moving subjects as you say. What happens when you activate it exactly that doesn't work? I can't say if it's your camera, but my D200 was pretty dreadful at tracking focus, the D300 seems a lot better.
 
trapper501 said:
I've only recently noticed people on here talking about the multiple focus points being used when tracking a subject. Could somebody explain how that works? I don't mean how does the camera achieve it but what is happening when you choose multiple points?
Click to expand...
Well you could of course just choose servo focus and one centre AF point, which would obviously be highly accurate as long as the system is fast enough to maintain focus, but trying to keep that single AF point over a fast moving target , particularly a smaller target such as a flying bird, can be well nigh impossible, especially when you really want the point of focus to be on the head.

Having multiple focus points selected means that once focus lock is achieved, even if you lose the birds's head with that initial AF point, it should be picked up and passed to one of the surrounding ones and so on to maintain focus.

With modern lenses passing distance info to the camera,the system should be able to choose the closest part of the bird to focus on and use the appropriate AF point when several of them fall over the subject.

Hope that helps?
 
I use all of the focus points in the camera. I rarely use the middle, because my subject is rarely composed in the center. I have got prety good at choosing without having to remove my eye from the view finder.

Focus-recompose is completely useless when you want critically sharp pictures below f2.8

Even the slightest recomposition can soften the image.
 
If your photographing a landscape how does multiple focus points work?
Does it adjust the aperture and therefore depth of field depending on distance between the points of focus?
Also what happens if your using aperture priority mode and have a large aperture set what happens if multiple focus points are achieved how does it maintain focus?
 
Yes, I also wondered about this. I was using a 1.4 lens at a gig and it kept on popping into my head, centre point or all points? If you use all points with a big apeture and are fairly close for a portrait shot where does the lens actually focus?

Dunc

RBHD1 said:
If your photographing a landscape how does multiple focus points work?
Does it adjust the aperture and therefore depth of field depending on distance between the points of focus?
Also what happens if your using aperture priority mode and have a large aperture set what happens if multiple focus points are achieved how does it maintain focus?
Click to expand...
 
I've done few studio shoots and always focused on the models eyes using the centre focus point, half pressed the shutter and then recomposed the shot. I've had a lot that look soft so with whats been said using the other focus points and not recomposing should help with the sharpness of them ?
And I presume this would be the same for other subjects as well ?
 
Duncan.F said:
Yes, I also wondered about this. I was using a 1.4 lens at a gig and it kept on popping into my head, centre point or all points? If you use all points with a big apeture and are fairly close for a portrait shot where does the lens actually focus?

Dunc
Click to expand...

usually for nikon camera it's 'closest subject priority' - it will focus on whichever AF point has the closest subject. The camera cannot focus on more than one point at once but can CHOOSE from all the points though! For canon cameras I think there is a mode where it chooses the correct aperture for the user's desired depth of field (A-Def?? Maybe) but being a Nikon user I'm not entirely sure about it..maybe someone else can expand.
 
Cheng said:
Sorry, I don't understand your question. To clarify, more AF points allow you to compose then focus, rather than focussing then recomposing.
Click to expand...

my question is what is one focussing on...what the camera wants or what the photographer wants
i admit i dont fully understand the practicalities of this..just that i usually focus on a point...with the little [ ] then recompose...i adjust exposure manually by using the +/-

now...perhaps i can understand if this is correct....you compose...the use some means to select from various focussing points on the screen...how is that done...which is the area you want to be sharp...??

then shoot the shot...

subjective
objective

thats how i look at it...what is the object of the photographer
 
Yeah Cannon cameras do have have a depth of field mode,where by it adjusts the depth of field to keep all points of focus sharp.
Also choosing your focus point with a Cannon is easy as there is a dedicated button and you just pick which focus point you want using the cursor keys.I think,but maybe I'm wrong in live view mode you can pick any focus point you want on screen (I know you could on my old Fuji).
The problem is in multi point mode rather than spot mode, what happens when you have a shallow depth of field and multiple points of focus selected by the camera,which one is in focus?
 
Multi af selection is very good in AI servo as the odds are you will contantly have the subject covered.
 
There was/is a thread with a poll somewhere on here, whereby you will find that most people tend to use primarily the center AF point then recompose, however, manually selecting another AF point is often required at times. Using all AF points and letting the camera select one it thinks you need, is a bit too much of a hit and miss for me.
 
RBHD1 said:
The problem is in multi point mode rather than spot mode, what happens when you have a shallow depth of field and multiple points of focus selected by the camera,which one is in focus?
Click to expand...

This is a camera specific question - you will need to refer to your camera manual or find a guide online that will explain to you the cameras AF system. Which camera are you enquiring about?

For the D300, you always start with an 'initial' sensor even with multiple sensors.
With the D200, if you had a group selected, you could choose between closest subject for the group, or between an initial 'starting' sensor.

So its camera specific...
 
Cheng said:
This is a camera specific question - you will need to refer to your camera manual or find a guide online that will explain to you the cameras AF system. Which camera are you enquiring about?

For the D300, you always start with an 'initial' sensor even with multiple sensors.
With the D200, if you had a group selected, you could choose between closest subject for the group, or between an initial 'starting' sensor.

So its camera specific...
Click to expand...

Good point,I will check my camera manual,but I guess the main thing I have gathered from the replies on this thread is that for a stationery subject use spot focus wether that be centre spot or one of the other selectable points. Then for moving subjects use the auto (multi) focus points and turn on continuous focusing.
At least I have learnt some new stuff, cheers!!
 
clicktor said:
There was/is a thread with a poll somewhere on here, whereby you will find that most people tend to use primarily the center AF point then recompose, however, manually selecting another AF point is often required at times. Using all AF points and letting the camera select one it thinks you need, is a bit too much of a hit and miss for me.
Click to expand...

I've had this
shooting an event, two lovely hooters ladies, and a metre behind them, right between then...a bit of writing.
the writing was in perfect focus! great

fortunately I always take 2-3 shots of them and shuffle the zoom slightly forcing the camera to re-focus with group shots like this
thank goodness for digital with amateurs like me around :bonk:
 
this must be a hell of an advantage (y)


CT said:
Well I think the advantages for composition have been covered.

The thing about the 7D is that it's the first camera ever from Canon which enables you to gain focus lock on a moving subject with any of the 19 AF points. After focus lock is obtained, the system will pass focus from one AF point to another to keep focus lock as the positoion of the subject changes within the pattern of AF points, so it's a major improvement if it lives up to it's promise and should be a boon for bird in flight shots where movement can be erratic.

All previous Canon cameras - even 1 Series with 45 AF points, require you to first obtain focus lock with the centre AF point before it will pass focus to other AF points.
Click to expand...
 
If I may, Joe on nikoncafe compliled an excellent post regarding the various focus modes on the D700.

I suspect it's similar for Canon, and the point about the 7D being able to track across the 45 AF points without having to start in the middle is a valid one. (The Nikon system doesn't have that limitation AFAICR).

http://www.nikoncafe.com/vforums/showthread.php?t=196906

Well worth a read in my opinion :)
 
Personally, I don't rely on the camera picking the right focus point as it can get it wrong and by the time I've gotten it to pick the right one, the moment (and my shot) is gone. I always pick one of the AF points myself.

Now... regarding people saying they use the centre point and then recompose. This might be fine under ideal conditions but if you're using a large aperture, focus and recompose can screw your focus in a big way because when you recompose you're changing the focal distance. If you have razor-thin depth-of-field and need to nail your focus, recomposing the shot with the focus locked in will mess things up royally. There's a good article about it here: http://visual-vacations.com/Photography/focus-recompose_sucks.htm

It's a pain having to keep switching AF points but it's worth it if you have to use a large aperture. Takes a bit of practice but it's pretty easy on Canon systems at least as the AF selection button is under your thumb and you can change it with the dial quickly. Just a shame that the spot metering zone isn't tied to the AF point on most Canon systems but that's another discussion altogether.

George.
 
BadgerLover said:
Personally, I don't rely on the camera picking the right focus point as it can get it wrong and by the time I've gotten it to pick the right one, the moment (and my shot) is gone. I always pick one of the AF points myself.

Now... regarding people saying they use the centre point and then recompose. This might be fine under ideal conditions but if you're using a large aperture, focus and recompose can screw your focus in a big way because when you recompose you're changing the focal distance. If you have razor-thin depth-of-field and need to nail your focus, recomposing the shot with the focus locked in will mess things up royally. There's a good article about it here: http://visual-vacations.com/Photography/focus-recompose_sucks.htm

It's a pain having to keep switching AF points but it's worth it if you have to use a large aperture. Takes a bit of practice but it's pretty easy on Canon systems at least as the AF selection button is under your thumb and you can change it with the dial quickly. Just a shame that the spot metering zone isn't tied to the AF point on most Canon systems but that's another discussion altogether.

George.
Click to expand...

a cross to bear for technology's sake
 
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