Tooslow
newbie
Reged: 12/01/2007
Posts: 24
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Can anyone please explain to me the benefit of large numbers of auto focus points? This isn't a criticism, it's ignorance and a wish to learn.
I'm getting on great with my D60, my first DSLR, it's easy to use and it's slowly getting "customised" to suit my needs as I learn what it can do. Sometimes I even read the manual! But I am puzzled by the supposed benefit of large numbers of auto focus points. I'm used to having one, so three on the Nikon seems like luxury. I've found it tends to auto focus on what is nearest, which may not be what I want to focus on. It can then fight back when I try to move the focus point so I've set it to manual selection. Even so I find myself slipping into the old habit of pointing the camera at what I want to focus on, locking the focus, reframing and shooting. So, back to my original question, what's the benefit of large numbers of auto focus points?
Thanks
JH
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IvorETower
Little Buttercup
Reged: 15/11/2006
Posts: 1759
Loc: Camberley, Surrey
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1. It's a marketing ploy;
2. If you are shooting action shots of fast-moving something-or-others that change direction unpredictably and rapidly, the camera focusing algorithms may be able to track the intended subject as it moves in the viewfinder- assuming that you can also keep said subject somewhere in view.
I have never found "just" 3 AF points of my D40 to be a problem
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Too many cameras, too many lenses.......
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Malcolm_Stewart
Carpal \'Tunnel
Reged: 11/07/2005
Posts: 2578
Loc: Milton Keynes, UK
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I had just 3 well separated points on my film EOS 50E and using the evaluative metering and the eye-control I was able to achieve focus off-centre, and the exposure was biased towards the subject matter under the focus point. Good feature and it worked.
Since then I've many more in an EOS3 and 1D MkIII - do I use them? No, I stick to the centre one. The EOS 3's many closely spaced points couldn't cope with my bifocals, and I only use the extra ones on the 1D MkIII as assist points which widen the active AF area if the chosen point is struggling. My EOS 30V film SLR has 7 and the eye control selection works well - pity that it arrived when DSLRs were just about here.
It was a good marketing ploy for a period. Same goes for the multiplicity of "exposure cells".
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Malcolm Stewart
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9463
Loc: Sussex-by-the-Sea
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I have cameras with anything up to 9 AF points and yes most of the time I just use the centre point. I very rarely allow the camera to auto select it's own AF point because it either selects the wrong subject (usually the closest but sometimes one with the highest contrast) or 'optimises' the focus across two or more AF points - which I've come to the conclusion seems to result in it being not right for any...
The more points you have the slower it becomes to select the one you want. TBH 3 seems about optimal. Scrolling around 9 can be a bit slow. Easiest is my EOS5 with eye control where selection is fairly rapid despite having 5 points (except that eye control doesn't work vertically and occasionally lighting conditions can confuse the eye control sensor).
Advantages to multi points? Some of the pro cameras have a lot more than 9 and with very sophisticated control routines are extremely good at follow focus with moving subjects.
I also find that when using the camera on a tripod it's sometimes more convenient to select an off centre AF point than focus with the centre point and then try to move the tripod head to recompose without releasing the shutter button and thereby losing focus lock...
With shallow depths of field and/or at short camera to subject distances focusing with the centre point and recomposing can introduce small focus errors due to the slight changes in distance that can occur as you change camera angle between focusing and recomposing - sometimes it's better to use an AF point on or closer to the subject to minimise this change.
I also find that when taking pictures of people in the vertical format if I use an AF point closer to the frame edge I generally get better compositions. All too often if I use the centre point in this situation I tend to get the subject in the middle of the picture with a lot of waste space above them...
All in all for general, ready-for-anything, photography you can't beat leaving the AF on centre - but the extra points can be handy to have in more considered situtions...
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Nigel
Completely BSRIPN 
ElSid Gallery
A camera in the hand is better than one in the cupboard........
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Benchista
Wich Tyler
Reged: 11/08/2000
Posts: 37849
Loc: Everywhere and nowhere, baby
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I've got a slightly different take. I've got cameras with varying different numbers of AF points, up to 45 on two cameras, EOS 3 and 1V. Several of my cameras have eye-controlled focus - EOS 5, 50E, 3 and 30V in order of release. ECF, if it works for you, makes a large number of focus points really useful - the camera focuses on what you look at. Equally, the 1V's auto selection works remarkably well. All that's great for action, when manually selecting focus points is a nightmare, even with joystick selectors. With other cameras, I pre-select the point I want to use - generally the central one.
Marketing gimmick? No, definitely not. Useful all the time? Again, definitely not. Sometimes the difference between getting a sharp shot or not? Yes. Only you can work out what that means for your mix of photography - in all honesty, it's not very important to me very often.
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Nick
www.nbrphoto.com
Light and Shade II - the new blog
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daft_biker
Action Man!
Reged: 11/10/2006
Posts: 7668
Loc: Doon the glen
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Quote:
....except that eye control doesn't work vertically....
I can't comment on the 5 but am sure the ECF on the 3 works fine vertically. IIRC the manual has a note in it to say that the eye control will need calibrated for both landscape and portrait shooting seperately.
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Andrew (BSRIPN) ... Pics.
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Benchista
Wich Tyler
Reged: 11/08/2000
Posts: 37849
Loc: Everywhere and nowhere, baby
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Quote:
Quote:
....except that eye control doesn't work vertically....
I can't comment on the 5 but am sure the ECF on the 3 works fine vertically. IIRC the manual has a note in it to say that the eye control will need calibrated for both landscape and portrait shooting seperately.
It doesn't work vertically on the 5, it does with all the other ECF-enabled cameras.
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Nick
www.nbrphoto.com
Light and Shade II - the new blog
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9463
Loc: Sussex-by-the-Sea
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^^^
WHS
The 5 is a bit odd in that it ran for many years with this limitation - even after cameras with ECF that operated both ways up had been introduced...
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Nigel
Completely BSRIPN
ElSid Gallery
A camera in the hand is better than one in the cupboard........
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PapaLazarou
Mr Joyful
Reged: 04/01/2006
Posts: 206
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I could never get it to work on the 5, it worked well enough on the 50e for me but there wasn't enough points for me to track in Ai mode, for my purposes, the 3 is just about damn near perfect, although to open up the full range of points you are best to use a lens with a fast max aperture and USM.
It's a feature i would like to see on DSLRs, as by the stage of the 3 and the 30/30v the technology seemed to be better, for me at least.
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9463
Loc: Sussex-by-the-Sea
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I do find it a bit surprising that a technology that had migrated down to 'advanced consumer' models like the 50E and 30 hasn't carried across to their equivalent digital models...
I rarely have trouble with my 5 even though I didn't do much of calibrating recommended in the book. It mainly seems to get a bit erratic if light levels are pretty low and occasionally shooting into the light can confuse it (too many eye reflections perhaps?...or maybe I should have done more calibrating...  ).
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Nigel
Completely BSRIPN
ElSid Gallery
A camera in the hand is better than one in the cupboard........
Edited by El Sid (23/07/2008 17:04)
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