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Old Sep 3, 2007, 7:41 PM   #1
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When I take a pic, I am focusing on one specific spot, than frame the picture, then fire. I basically only use one single focus point.

Which are the cases when people need 51 focus points ?
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Old Sep 3, 2007, 8:33 PM   #2
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Slow autofocus is one of the main complaints people have with cameras.When comparing models,those with more AF points are able to find something in the scene on which to focus. Presumably 51 AF points will make for nearly instant focus, yes? Of course, you still have to decide if it is the right something.

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Old Sep 3, 2007, 8:38 PM   #3
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Because Canon's top of the line cameras only have 45 focus points. 51 is a higher number and that sounds better in Nikon's marketing material. ;-)

OK -- If you have more focus points, you have less chance of needing to reframe in order to find a focus point to place on your intended subject. For example, someone's eyes versus their body when you're shooting at wider apertures where depth of field is very shallow

More focus points also allows the camera to track a moving subject better, automatically switching focus points within the frame to keep them locked in focus as they move. Sports photography is a good example of where that can come in handy.

But, you have to look at the quality of the focus points and algorithms being used, not just the quantity of the focus points. Nikon and Canon are both very good in this area. So, I wouldn't worry about the difference in the number of focus points too much if you decide on a camera with less than 51 focus points. lol The more important aspect would be how well the AF system works overall.


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Old Sep 4, 2007, 4:57 AM   #4
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Another area where it will be very useful is for birds in flight (BIF) as you will be able to keep a focus point over the bird while trying to track, however personally I'm not convinced that 51 is essential.... 20 would easily cover the majority of the frame and if positioned well 9 does a good job..... as Jim says a lot of what goes on in the market place is all about getting one up on the competition which Nikon have surely done with the new models coming out.
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Old Sep 4, 2007, 8:36 AM   #5
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JimC wrote:
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Because Canon's top of the line cameras only have 45 focus points. 51 is a higher number and that sounds better in Nikon's marketing material. ;-)

OK -- If you have more focus points, you have less chance of needing to reframe in order to find a focus point to place on your intended subject. For example, someone's eyes versus their body when you're shooting at wider apertures where depth of field is very shallow

More focus points also allows the camera to track a moving subject better, automatically switching focus points within the frame to keep them locked in focus as they move. Sports photography is a good example of where that can come in handy.

But, you have to look at the quality of the focus points and algorithms being used, not just the quantity of the focus points. Nikon and Canon are both very good in this area. So, I wouldn't worry about the difference in the number of focus points too much if you decide on a camera with less than 51 focus points. lol The more important aspect would be how well the AF system works overall.

2 critical points here I want to back up.

1. Less need for focus & recompose - at shallow DOFs simple geometry tells us that focus & recompose will lead to errors.

2. Quality is important too. Speaking just within the Canon system, let's take 2 of the latest announcements from canon - 1dmkIII and 40d. The mkIII has 19 focus points that are cross type (detect phase shift & contrast along both axis) and all 19 are high precision (meaning they are more accurate with 2.8 lenses). The 40d has 9 cross-type but only the center one is high-precision. This means on the mkIII there are 19 points I can use that are all just as accurate as the center point - on the 40d the center point is still the only high precision point. Also, the 1-series cameras have a separate processor that controls AF. The 40d does NOT have this - it's not something you see in specs much and reviews don't cover it but it's what makes the 1d focusing that much better. It's critical to servo processing success. Think of it like a computer - having a graphics card is critical to rendering graphics timely - same with AF.

also want to add a few more

3. focus & recompose doesn't work for moving subjects like moving wildlife or sports - so having more focus points to choose from provides a better framed photo so less cropping is required. I really didn't like the positioning of the focus points on my 20d - having 19 points to choose from instead of 9 is definitely a bonus

4. "helper points" - both canon and the new nikon allow you to specify whether helper points can be used - rather than using all 45 or 51 you use just the points surrounding the selected point - so you get some help if the subject moves from the point you're using but won't get as confused by points in other parts of the frame. So, for instance on the new MKIII you can only select 19 points the other 26 are just 'helper points' - you can turn them on or off as you wish.

5. customizations about how quickly the camera will switch to something in the foreground. For some things you want the quickest focusing possible and you're confident you won't have an object come between you and your subject (baseball for me is like this) but in others you can have constant interferance and you don't want the camera switching (swimming where splash often appears between subject and you).

Having said all this - it still comes down to whether a given photog needs the feature. It's extremely helpful for high quality action photography and definitely beneficial for shallow-dof still photography. If you don't plan on either of those types of photography then it's not a feature that is likely to benefit you.
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Old Sep 5, 2007, 8:14 AM   #6
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Mark1616 wrote:
Quote:
Another area where it will be very useful is for birds in flight (BIF) as you will be able to keep a focus point over the bird while trying to track, however personally I'm not convinced that 51 is essential.... 20 would easily cover the majority of the frame and if positioned well 9 does a good job..... as Jim says a lot of what goes on in the market place is all about getting one up on the competition which Nikon have surely done with the new models coming out.
Having more AF point is somewhat flexible, but not always... :idea:

What's being described so far only work based on the assumption that the camera can track the subject, but in real-life things are not that black an white: Unless you're shooting a big blue heron for example most birds in flight are quite tiny, the size of a baseball or less, and these birds tend to become even more streamline as they take flight - A 45 (or 51) AF points on my MrKII just mean the majority of the remaining 44 AF points will try to lock on something else instead of the bird as everything will appear to be valid moving subject(s) to the camera

I usually forced the camera to a single point AF to shoot bird in flight especially when they are fast movers - For larger subjects covering many AF points at a time so the camera can track is OK, but using all 45 (or 51) AF points for small subjects in flight is just an execise in futility IMO: http://forums.steves-digicams.com/fo...mp;forum_id=11
-> Try to shoot a tiny ball in flight for example vs a large players running for example and you can see how the AF work (or not)


Of course most cameras will allow you to customize, or to group the AF points together to be more effective, but that presume you already know what the size of your target is. In nature you just don't know what's the shape/size of your next subject can be and making an AF point larger actually makes the AF less selective as usually the now 'larger' AF point will pick up more on the contrasty branches or foliages instead of the actual bird...

May be they should add another button where one can elect to use/or not the expanded area!
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Old Sep 7, 2007, 11:27 AM   #7
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focus & recompose doesn't work for moving subjects like moving wildlife or sports - so having more focus points to choose from provides a better framed photo so less cropping is required.

It sound to me that there is something more basic that makes me miss the point. To take a bird, do you guys just select AF, point at the bird and shoot, leaving the helpers points to do the rest ?? You are not doing any AF pre-focus for moving subjects ?

Sorry, I am confused. Thanks for your patience

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Old Sep 7, 2007, 11:41 AM   #8
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Phil,

there isn't a single answer to your question. First I would suggest the answer depends on what type of bird and how far away (i.e. how much of your frame it fills) and second what the bird is doing - sitting ona branch vs. flying.

Also it matters what the background is. For instance a bird against the clear sky is much easier for the camera to 'pass' focus from one point to another - but with confusing background if you allow the camera to use more than one point then you have the potential for the camera to mistakenly switch to something in the background to focus on.

You'll also get into technique differences. Some people prefer taking a single shot of a bird that isn't changing focal planes so they don't use ai-servo. Others prefer head-on shots with the bird coming toward them and thus changing focal planes and maybe prefer to take a burst of shotsand thus requiring AI-Servo.

So, bottom line I think the answer depends on what your subject really is, what the subject is doing, what the background is like, how far away you are, what the DOF you're using is. In other words there are a lot of variables at play. So I don't think there's a single RIGHT answer to the question.


Edit - Also , what I was refering to about focus-recompose is this - let's assume you are close enough or your subject is large enough that they fill 1/2 the frame. More often than not people prefer to focus on the head to get sharp eyes (rather than having a sharp wing tip). Now, as you track the bird in flight you can't lock focus then recompose so the bird's head is forward of center. If the bird is flying left to right you may want to select a focus point that is RIGHT of center so the shot is better composed in-camera. When you're shooting smaller birds and need quite a bit of cropping it matters less.
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Old Sep 8, 2007, 7:48 PM   #9
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Quote:
If the bird is flying left to right you may want to select a focus point that is RIGHT of center so the shot is better composed in-camera
Thx a lot John, I had never thought about this technique.

I was indeed speaking about a bird flying on the same distance from left to right, as it happens most of the time on the beach. when birds like tochase fishes parallelto the shore line
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Old Sep 10, 2007, 9:22 PM   #10
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JohnGWrote:

Also it matters what the background is. For instance a bird against the clear sky is much easier for the camera to 'pass' focus from one point to another - but with confusing background if you allow the camera to use more than one point then you have the potential for the camera to mistakenly switch to something in the background to focus on.



I've missed many shots because the auto-focus point was focused on something other then what I was trying to focus on. Especially when shooting low light sports or "busy" backgrounds.

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