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Author Topic: 9 Autofocus Points versus 51 Autofocus Points  (Read 19456 times)

JohnKoerner

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9 Autofocus Points versus 51 Autofocus Points
« on: January 11, 2009, 08:02:28 pm »

Do most of you folks find having several AF points helpful or do you find them actually problematic? I am finding that turning them all off, and only having the center AF point active, is the quickest way to get my shot in focus. It seems to me that when I have them all turned on that oftentimes the "other" focal points dominate and concentrate on a part of the subject I could care less about, and in so doing blurring the part of the subject I do care about.

There have been debates regarding 9 AF points vs. 51 AF points, but I am finding only having 1 suits me just fine. I am curious if others feel the same way or if I am just missing something important?

Thanks for any feedback.
« Last Edit: January 11, 2009, 08:05:47 pm by JohnKoerner »
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carl dw

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9 Autofocus Points versus 51 Autofocus Points
« Reply #1 on: January 11, 2009, 08:26:13 pm »

Quote from: JohnKoerner
Do most of you folks find having several AF points helpful or do you find them actually problematic? I am finding that turning them all off, and only having the center AF point active, is the quickest way to get my shot in focus. It seems to me that when I have them all turned on that oftentimes the "other" focal points dominate and concentrate on a part of the subject I could care less about, and in so doing blurring the part of the subject I do care about.

There have been debates regarding 9 AF points vs. 51 AF points, but I am finding only having 1 suits me just fine. I am curious if others feel the same way or if I am just missing something important?

Thanks for any feedback.

Agreed. A man with one watch knows the time, a man with two is never sure.

I shoot a lot of stuff with large aperture lenses wide open on a 1ds3, the additional focus points only made sense to me when a firmware update allowed them to be selected individually (with ease) with the 'joystick'. With a bit of thumb practice the process becomes quite intuitive.

I like the option of loads of focus points around the frame to aid focusing with different compositions, but only one at a time please.
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JohnBrew

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9 Autofocus Points versus 51 Autofocus Points
« Reply #2 on: January 11, 2009, 09:02:13 pm »

Quote from: JohnKoerner
Do most of you folks find having several AF points helpful or do you find them actually problematic? I am finding that turning them all off, and only having the center AF point active, is the quickest way to get my shot in focus. It seems to me that when I have them all turned on that oftentimes the "other" focal points dominate and concentrate on a part of the subject I could care less about, and in so doing blurring the part of the subject I do care about.

There have been debates regarding 9 AF points vs. 51 AF points, but I am finding only having 1 suits me just fine. I am curious if others feel the same way or if I am just missing something important?

Thanks for any feedback.

Having owned my share of AF cameras I couldn't agree more. None of the cameras I own today have AF.

kbolin

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9 Autofocus Points versus 51 Autofocus Points
« Reply #3 on: January 11, 2009, 09:20:49 pm »

I agree... my default is the center focus point and using the joystick to move it around as needed.  Only occasionally will I turn on all focus points, usually in high speed sports action situations but I rarely do sports.


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fike

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9 Autofocus Points versus 51 Autofocus Points
« Reply #4 on: January 11, 2009, 09:23:09 pm »

Another in the agree camp.  Auto Focus, hold focus, and recompose is my mantra.  I have recently experimented with using the joystick selector for focus point selection, and I find it mostly novel.  On the other hand, when I allow the camera to pick the focus points, it invariably picks the wrong one.   I like to pick the focus point myself.
« Last Edit: January 11, 2009, 09:23:39 pm by fike »
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JohnKoerner

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9 Autofocus Points versus 51 Autofocus Points
« Reply #5 on: January 11, 2009, 10:10:57 pm »

Okay, I am glad I am not alone in this then (I thought maybe I was misusing the feature or something).

Autofocus is important to me because one of my hobbies is to "collect butterflies" with my camera. Some species are so common that I get many, many opportunities to film them. Therefore, if I miss a shot on one specimen, another will soon be back to take its place later on. However, some butterfly species are extremely rare (or even considered "out of range") in my area, and so I may only get "one" chance to photograph a particular specimen if I see one. Again, this is especially true if the specimen is considered a "stray" from its normal geographic area. Thus I find AF critical in getting the shot quickly, if it lands, lest such a rarity "fly away" before I am finished fooling with manual focus, etc.

I had one such opportunity the other day, as it is still warm enough in FL to see buttterflies even in winter. When I tried to take the shot, the AF (with all 9 focal points active) missed the subject and instead one of the points focused on a blade of grass. Fortunately, I was able to get the shot manually, but it made me stop and think about what if the specimen had flown away and I had blown my only opportunity? It was at that point that I started seeing the 9-point AF as a possible hindrance to getting a "once in a lifetime" shot, if the wrong focal point zeroed-in on the wrong thing. Since then I have used only the center focal point and now I find that just using that "one" focal point to be perfect for my needs, and the rest of them to be superfluous (even annoying).

I do see how, compositionally, maybe using one of the surrounding AF points would be handy, but again only one at a time. I was quickly forming the opinion that (for the most part) having 9 ... or Heaven forbid 51 ... AF points is really kind of a cluster$@&# rather than an asset to a photographer.

So I wanted to see if others were in agreement  

Jack
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stever

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9 Autofocus Points versus 51 Autofocus Points
« Reply #6 on: January 11, 2009, 11:04:37 pm »

john, i presume you're using the af-on button or have re-programmed the * button for autofocus so that focus is independent of shutter actuation - allowing you to focus and re-compose

i don't think many wildlife photographers use other than the central spot for focusing - your blade of grass is a very typical problem.  the other problem is that the 100M is a slow focusing lens even though it's f2.8, you'll get noticeably faster focusing with the central spot
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DarkPenguin

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9 Autofocus Points versus 51 Autofocus Points
« Reply #7 on: January 11, 2009, 11:47:29 pm »

Helpful.
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JohnKoerner

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9 Autofocus Points versus 51 Autofocus Points
« Reply #8 on: January 12, 2009, 12:07:01 am »

Quote from: stever
john, i presume you're using the af-on button or have re-programmed the * button for autofocus so that focus is independent of shutter actuation - allowing you to focus and re-compose

Well, in the one instance, I just shut off the AF and took the shot. Since then I just use the central focus dot and have never had a problem since.




Quote from: stever
i don't think many wildlife photographers use other than the central spot for focusing - your blade of grass is a very typical problem.

As I learned  

I saw all the debates and complaints about Canon having "only 9" AF points, and to me my complaint is that it has more than one. I am learning as I go and I quickly realized all the AF points are a pain, but that just one is wonderful.




Quote from: stever
the other problem is that the 100M is a slow focusing lens even though it's f2.8, you'll get noticeably faster focusing with the central spot

Wow, that sure is the exact opposite of my experience. My 100mm macro AF is fast as hell. It zeroes-in and locks-on in less than half a second. In fact, the Photozone review concurs by saying, "The AF speed is blazingly fast":

http://www.photozone.de/canon-eos/167-cano...-report--review

Are you sure you're not thinking of the Canon 180mm macro? That lens is always referred to as "slow," but the 100mm is very fast. Mine sure is anyway  

Thanks,
« Last Edit: January 12, 2009, 12:19:59 am by JohnKoerner »
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Yoram from Berlin

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9 Autofocus Points versus 51 Autofocus Points
« Reply #9 on: January 12, 2009, 03:48:04 am »

I have recently begun using multiple AF points. I never got the point of it, but have changed my mind on this.

I've been shooting kids with a fast wide angle lens wide open (24mm /1.4), and have found that multiple AF points help me get the focus quicker. Children move so fast there's little time to recompose, and the multiple AF points allow me to compose and shoot more quickly.

Don't dismiss it entirely... but like a lot of you, I still go back to center AF point for a lot of my work.
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NikosR

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9 Autofocus Points versus 51 Autofocus Points
« Reply #10 on: January 12, 2009, 04:57:18 am »

Different systems for different needs. That's why you're getting options. Ask some sports-shooters or BIF shooters if having a good performing predictive tracking system with many AF points is not beneficial in many circumstances.

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Nick Walker

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9 Autofocus Points versus 51 Autofocus Points
« Reply #11 on: January 12, 2009, 06:33:34 pm »

Quote from: JohnKoerner
Do most of you folks find having several AF points helpful or do you find them actually problematic? I am finding that turning them all off, and only having the center AF point active, is the quickest way to get my shot in focus. It seems to me that when I have them all turned on that oftentimes the "other" focal points dominate and concentrate on a part of the subject I could care less about, and in so doing blurring the part of the subject I do care about.

There have been debates regarding 9 AF points vs. 51 AF points, but I am finding only having 1 suits me just fine. I am curious if others feel the same way or if I am just missing something important?

Thanks for any feedback.


Modern AF systems are complex, it is important to learn which combination of AF options to select for the task in hand.

I routinely tweak the AF system for different sports. I never use multiple AF points for portraits and static subjects, unless during action I am tracking someone who comes to an abrupt halt and don't have time to switch the AF system to a single AF point. At closer working distances (e.g.portraits) it is very important to compose the image and then select a single AF sensor to meet the required point of focus (focus on eye), not just use the central AF sensor then recompose the image as the critical point of focus will shift.

Multiple AF sensors used in the right circumstances for unpredictable action photography can be a better solution than relying on one AF sensor. Choosing 9, 21, or 51 AF points is subject and movement dependent. When framing tight on a tennis player (chest up) I will stick to one AF sensor on the face with the normal or long delay lock-on (depends on shooting angle) - I do not want the tennis racket, as it is drawn across the frame, to disturb the AF. If I am framing full length to anticipate a full stretch shot, or player diving for the ball, I will employ 9, or 21 AF sensors as the backgrounds are often plain and will not throw-off the multiple points. With a plain background, 51 3D AF tracking should be perfectly suitable (in theory) when framing full length subjects. Tighter framing where the depth of field is only inches with a 400mm F/2.8, or 600mm F/4 lens at full aperture (even stopped down a little) is a hit and miss affair with multiple AF points, in comparison to an accurately targeted single AF sensor.

No professional sports photographer can guarantee keeping a single AF sensor on an unpredictable moving subject. Should that AF sensor miss the subject momentarily the focus will shift instantaneously beyond the subject. Intelligent multiple sensor AF systems are designed to try and stick with the subject and the reason why Nikon advocate multiple AF sensors to stop the AF wandering to the background (it still fails on occasions). I recently saw a very good image of a rugby player diving straight at camera taken by an accomplished photographer. The photographer was using one AF sensor; the most stunning shot was two frames earlier but the photographer (not AF system) had lost focus onto the background. Fortunately he recovered the situation, although the very best shot escaped him. This is not to say that the multiple AF points would have nailed the subject's face pin sharp as an AF system can only predict!
 
Nikon's 51 3D Dynamic AF System.

A very knowledgeable member of Nikon's (UK) pro team explained this system to me using Pin Art as an analogy  - http://en.wikipedia.org/wiki/Pin_Art Nikon's D3 51 point 3D AF system is using, colour, contrast, and distance data, to track the subject. The 51 AF sensors work in a similar fashion to 51 rangefinder devices, whilst plotting its 3D map using, contrast, colour, and distance data of the subject.

My tests using 51 3D AF tracking with its advanced colour scene recognition technology reveal that it works for some static and slower moving objects, however under certain conditions the system always favours contrast over the initial colour that it was targeted to analyse. In perfect light, photographing kite surfers, the 51 3D AF system would only stay on the kitesurfer's head or torso, momentarily - even with colourful tops, camouflaged patterns and excellent additional contrast from large zips and harnesses. The AF regularly jumped to the white sunlit sea spray created by the kitesurfer's wake, indicating contrast dominance over its colour analysis.

Here is an interesting link from an D3 review by Dr Alex Mustard, an accomplished underwater photographer who initially disliked the 51 3D AF system but then found it very useful for macro work - http://wetpixel.com/i.php/full/nikon-d3-fi...ific-part-2/P3/

Another D3 article, by Dave Black - http://www.daveblackphotography.com/workshop-at-the-ranch/140-workshop-at-the-ranch-february-2008-the-nikon-d300. He seems to find the D3 and D300's, 51 3D tracking useful. His surfer shot is a typical example where the 51 3D tracking 'may' fair better due to the subject to camera distance (only 70-200mm + 1.4X though) with a more forgiving F7.1 aperture - background wave and other areas in close proximity to surfer. During my kitesurfer 51 3D AF tests I used a 400mm lens with and without a 1.4 converter at F4 - F5.6. Much tighter framed the AF routinely jumped to the strongly sunlit sea spray - very narrow depth of field due to lens choice, aperture and subject to camera distance taxed the 51 3D Af tracking system.

My feeling on the 51 3D tracking is that Hiroshi Takeuchi at Nikon has achieved an amazing technological feat by combining contrast, colour and distance AF calculations - http://imaging.nikon.com/products/imaging/...19/index_02.htm. However IMHO for faster moving subjects at closer distances using larger aperture telephoto lenses this may require the next generation system with much faster computing power and finer colour data (many more RGB pixels reading the data) to calculate from the subject matter - thats not to say that the current version is not worth employing, it just has its limitations.

Focus tracking with lock-on options

Setting multiple AF sensors with the focus tracking lock on set to 'off' will defeat the camera's dynamic AF capabilities - multiple AF sensors are designed to work with long, short, or normal settings to keep contact with the subject. If you are using a single AF sensor on a single subject, OFF may be appropriate under some circumstances - if you loose contact with the subject however the AF will instantaneously jump in most cases to the background.

Examples -  

Football match where the movement is unpredictable and the subject may only be temporarily blocked - normal lock-on timer settings - 9 or 21 points, normal lock-on setting.

Cricket match or Baseball game where there is less chance of a player crossing the path of another - fast lock-on setting enables swifter AF response when changing from one player to another at different locations on the field of play - 9 or 21 AF with fast lock-on.

Runners, as they move along their respective running lanes will often overlap each other in the frame a long lock-on setting would be more appropriate - 9 or 21 AF points.

The above examples are guides, a particular AF set up carefully considered for a certain type of action can be tripped up by unexpected circumstances. Someone else will swear by other AF methods.

Release or Release + focus priority?

Release (CF A1) - enables quick shutter and frame rates.

Release + Focus still provides quick shutter response but will slow down the frame rate to help improve the focus in poor lighting and subjects with lower contrast.

To cap it all I use a singe AF sensor 70% of the time, including action, rarely ever the central one, as it forces sloppy working practices regarding composition; even though the outer AF sensors on the Nikon D3 are not cross sensitive - varying between release and release priority. The remainder of the time I use either 9, or 21, AF points and regularly vary the lock-on, and release options.
« Last Edit: February 26, 2012, 06:34:44 pm by Nick Walker »
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OldRoy

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9 Autofocus Points versus 51 Autofocus Points
« Reply #12 on: January 13, 2009, 06:11:48 am »

Nick
thanks for taking the time to compose this very lucidly expressed and useful summary.
Roy
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Robert Roaldi

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9 Autofocus Points versus 51 Autofocus Points
« Reply #13 on: January 13, 2009, 11:53:06 am »

Just wanted to add my thanks, Nick. Best explanation I have ever read.

I have an Oly E-1 and have not been able to find a description of how the 3 AF points are supposed to work together. Unless I can understand how the system is designed to work, how can I decide how to make use of it? The normal manuals are useless.
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JohnKoerner

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9 Autofocus Points versus 51 Autofocus Points
« Reply #14 on: January 13, 2009, 12:57:01 pm »

That was a tremendous breakdown, Nick, thank you.

In re-reading my 50D manual, it essentially said the same thing (though not so detailed or eloquently  ).

This means the answer to my original question was mis-use; I was misusing the autofocus. My attempts to focus were on stationary objects, not moving ones, which is why the AF was hindering me and not helping me. In the future, maybe if I am trying to capture birds in flight etc. I will remember what the multiple AF points are for and attempt to use the right tools for the right job.

It seems to me, if I am understanding both your counsel right, as well as my manual, that the multiple-AF points are useful precisely where movement is a concerned. For instance, Dr. Mustard in his review you posted stated that (for macro work) , "I identified two main (AF) uses (for macro work) – both more to do with camera rather than subject movement! First is intention camera movement, this mode is a great tool for recomposing a macro shot. You leave the main focus point in the middle of the frame, focus on the subject, recompose and the camera tracks the subject “movement” and then fire. The second is in high magnification macro with longer lenses where it is impossible to keep the camera totally still. Here the 3D tracking is excellent and following the small movements resulting from camera and keep the subject sharp."

Even in my manual it states to shoot only one "point," and that would be the point where it allows you to frame your subject as desired. I just choose the center point at this juncture because I am pretty much just trying to get as much of a tiny critter into my frame as I can, rather than take an overall "artsy" shot of a subject + background. For subjects that move the manual states of the 9 AF points, "This AF mode is for moving subjects when the focusing distance keeps changing. When you hold the shutter button halfway, the subject will be focused continuously".

Thus the multiple AF points can not only assist in macro situations with subject movement (crawling bug / moving fish), but where I anticipate some camera movement also. Interesting.

So thank you once again for taking the time to help me understand the feature. It's funny, they say you have to read a decent-sized book 5x to retain an average of 65% of the material. This is why I intend to read, and re-read, my manual until all of it is absorbed.

This forum is a great resource, really in many ways a better resource than the manual, because you get real-life perspectives that aren't as "dry reading" as a tiny manual in size-4 font  


Thanks again,

Jack
« Last Edit: January 13, 2009, 01:01:21 pm by JohnKoerner »
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Slobodan Blagojevic

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9 Autofocus Points versus 51 Autofocus Points
« Reply #15 on: January 13, 2009, 09:52:59 pm »

Quote from: fike
... Auto Focus, hold focus, and recompose is my mantra. ...

That technique might lead to out-of-focus results, as the focus plane may not be the same, especially in shallow depth-of-field circumstances.

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9 Autofocus Points versus 51 Autofocus Points
« Reply #16 on: January 20, 2009, 05:41:00 pm »

I just turn AF off 99% of the time.
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telyt

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9 Autofocus Points versus 51 Autofocus Points
« Reply #17 on: January 21, 2009, 10:12:54 pm »

Quote from: slobodan56
That technique might lead to out-of-focus results, as the focus plane may not be the same, especially in shallow depth-of-field circumstances.
Also when the subject is moving, even slightly.  My camera has an infinite number of eye-controlled focus points.  It's a matte plastic ("ground glass") viewscreen.
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NikosR

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9 Autofocus Points versus 51 Autofocus Points
« Reply #18 on: January 22, 2009, 03:34:14 am »

Nikon's own take regarding the D3 (and D700 I suppose) AF system:

http://nikonusa.com/pdf/manuals/dslr/D3ProTechnicalGuide.pdf
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