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Author Topic: Af-points, Nikon and Canon  (Read 8827 times)
Mike W
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« on: April 13, 2008, 08:16:26 AM »
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Hi Folks,

Lately I've been playing around with both Nikon and Canon camera's (40D and D300).
I'm used to a Canon 5D, which is the camera I use for the most part.

The Nikon D300 and D3 claim to have 51 points, the 40D has 9 points. Both work fantastic in my view. I mostly use manual focus, but it's nice to know it (AF) is there when I need it.

So the question is; is Nikon's 51 point system marketing-bs? Are the 51 points usable or are they just overkill? Since both camera's seem to do just fine, I'm struggeling to see if there is a point in having more AF-points.

regards,

Mike
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Tony Beach
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« Reply #1 on: April 13, 2008, 12:10:42 PM »
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The CAM3500 and its 51 AF sensors are not marketing hype.  Why do you suggest that the CAM 3500s 51 AF sensors are a "claim"?  The CAM3500 does have 51 AF sensors and I don't see on what basis you would dispute that.

One of my favorite AF settings on my D300 is 51 point 3D tracking which facilitates seamless "focus and recompose".  For static scenes being able to make precise choices about where to place the focus is not possible with only 9 or 11 AF sensors.  I find using 9 and 21 points Dynamic-area AF very useful for tracking erratic subjects that drift off the initially selected AF sensor.  For sports, birds and other fast moving subjects you can set the camera to 11 AF Selection and using 21 point Dynamic-area tracking you are able to quickly select the region of the frame you want to focus on using one of those 11 AF sensors as a starting point and the CAM3500 uses the neighboring AF sensors to track the subject.

If you mostly focus manually and don't avail yourself of sophisticated AF features, then I can see why you wouldn't understand or appreciate those features. If you have a 5D and there is nothing you want in a D300 that the 40D can't do, then you should stick with Canon and spend the extra money on glass instead.
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Farkled
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« Reply #2 on: April 13, 2008, 12:56:04 PM »
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I guess I just don't get the whole AF thing.  There is no way I could select an AF point while tracking a moving subject (well maybe a sleepy turtle) before the shot is long gone.  If I let the camera pick a point, it generally picks one that is furthest from intended subject.

In the days of manual focus, I simply used the ground glass for moving subjects, or prefocused, or used hyperfocal settings or all of the above.  With today's reduced viewfinder space and lenses that are not intended for manual focus, trying to focus manually on moving subjects ain't all that easy.

The only "solution" I have for the moment is to use the single center point for for focus all the time.  It also has the advantage of being where the spot meter is.  A half press does the focus/meter thing, recompose as needed and shoot.  There is more than enough complexity in that scenario to keep me busy and to reduce the keeper rate.  If the shot is static enough for me to mess around with selecting AF points then my method works as well and is faster.
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Tony Beach
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« Reply #3 on: April 13, 2008, 02:52:52 PM »
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I guess I just don't get the whole AF thing.  There is no way I could select an AF point while tracking a moving subject (well maybe a sleepy turtle) before the shot is long gone.  If I let the camera pick a point, it generally picks one that is furthest from intended subject.

In the days of manual focus, I simply used the ground glass for moving subjects, or prefocused, or used hyperfocal settings or all of the above.  With today's reduced viewfinder space and lenses that are not intended for manual focus, trying to focus manually on moving subjects ain't all that easy.

The only "solution" I have for the moment is to use the single center point for focus all the time.  It also has the advantage of being where the spot meter is.  A half press does the focus/meter thing, recompose as needed and shoot.  There is more than enough complexity in that scenario to keep me busy and to reduce the keeper rate.  If the shot is static enough for me to mess around with selecting AF points then my method works as well and is faster.
[a href=\"index.php?act=findpost&pid=189254\"][{POST_SNAPBACK}][/a]

Auto-area AF works very well for quick draw shots, with the camera giving preference to closest subject -- but closest subject is not always the best, which is where more nuanced configurations come into play.  The main caveat to using too many AF sensors is that it can slow down the camera's acquisition; and that, in addition to not always wanting the closest subject prioritized, is why using Auto-area AF is not a panacea to all AF situations.

There are 15 sensors on the D300 which are all equally capable; unfortunately they are all grouped into the center 3x5 portion of the available 51 sensors.  However, the surrounding AF sensors do fine under daylight conditions and are reasonably good in less than ideal light.

As I have already written here, by setting the camera to 11 Point AF Selection you can quickly select one of the 11 AF sensors displayed in the viewfinder.  My thumb moves effortlessly between the AF-ON button (which I use exclusively for focusing) and the Multi-selector button, and I have no trouble selecting and then tracking birds in flight using this technique.

On Nikon DSLRs the spot meter is under whichever AF sensor has been selected, so that is not a consideration.

The problem with traditional "focus and recompose" using AF-S is that the actual focus distance changes after the camera has locked focus.  By using 51 point 3D Tracking and AF-C instead, the focus adjusts as you recompose and you get more accurately focused shots.

I pretty much never use Single point AF on my D300.  For me it is always useful to use 9 or 21 points Dynamic-area AF tracking to give the camera a chance to maintain precise focus even when the originally acquired target has drifted off of the original AF sensor.  With all the configurable function buttons available on the D300, I have one set to quickly change Dynamic-area AF modes so I can dial in 9, 21 or 51 point 3D tracking in about two seconds -- this is not a big issue for me as I tend to stay in one of these tracking modes as long as I'm shooting a particular subject.

If your "keeper" rate is less than 98%, then you are shooting extremely challenging subjects and/or not fully understanding and utilizing the D300's capabilities.
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Mike W
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« Reply #4 on: April 13, 2008, 03:36:48 PM »
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Thanks for the replies everyone,

First off, I wouldn't claim that the Nikon 51 AF-spot system is merely marketing. I just had the thought that it MIGHT be marketing, as so many things in het market.
Or maybe that the 51 spots aren't really usable because it isn't very fast, or something.

I don't own the 5D, I rent one via my school. I'm looking into both Nikon and Canon to make a buy in the near future. I ask these questions because I want to learn, and because I'm curious to how these technologies work.

I've never used the AF point selector, but I will try it out soon. It sounds interesting

@Tony, do you notice any change in speed of focusing when using 51 point AF in contrast to the other modes?

regards,

Mike

 
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The CAM3500 and its 51 AF sensors are not marketing hype.  Why do you suggest that the CAM 3500s 51 AF sensors are a "claim"?  The CAM3500 does have 51 AF sensors and I don't see on what basis you would dispute that.

One of my favorite AF settings on my D300 is 51 point 3D tracking which facilitates seamless "focus and recompose".  For static scenes being able to make precise choices about where to place the focus is not possible with only 9 or 11 AF sensors.  I find using 9 and 21 points Dynamic-area AF very useful for tracking erratic subjects that drift off the initially selected AF sensor.  For sports, birds and other fast moving subjects you can set the camera to 11 AF Selection and using 21 point Dynamic-area tracking you are able to quickly select the region of the frame you want to focus on using one of those 11 AF sensors as a starting point and the CAM3500 uses the neighboring AF sensors to track the subject.

If you mostly focus manually and don't avail yourself of sophisticated AF features, then I can see why you wouldn't understand or appreciate those features. If you have a 5D and there is nothing you want in a D300 that the 40D can't do, then you should stick with Canon and spend the extra money on glass instead.
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Tony Beach
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« Reply #5 on: April 13, 2008, 08:59:23 PM »
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@Tony, do you notice any change in speed of focusing when using 51 point AF in contrast to the other modes?

regards,

Mike
[a href=\"index.php?act=findpost&pid=189278\"][{POST_SNAPBACK}][/a]

That depends on whether you are near the limits of the AF system or not.  For many situations the differences are insignificant, but for particularly challenging situations using 51 points becomes completely untenable whereas using 9 or 21 points Dynamic-area tracking can squeeze out more keepers.  The tougher the situation (less light, smaller target, faster moving, and closing in fast on you) the more incumbent it is upon you to take the bull by the horns and continually reacquire focus and rely on the center 15 AF sensors to acquire and track your subject.
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bvalente
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« Reply #6 on: September 30, 2008, 09:25:51 PM »
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Hi folks

This thread has been a bit helpful on my setting up AF for shooting birds in flight.

I want to share my settings and thoughts and see what folks think about my rationale, keeping in mind I'm shooting birds in flight. Hopefully this will help others too. I have the nikon D700.


AF-C (continuous focusing because my subject is constantly moving, usually towards or away from me)

AF sensor mode: crosshair (don't know the official name instead of 'crosshair' but allows me to choose the subject and then it tracks focus within a limited range)

dynamic AF area mode: 51 point 3d tracking (which I assume is for tracking movement, but I really don't know how it relates to AF sensor mode)

focus tracking with lock on - short (if it loses focus on the subject I want it to find it again fast)

AF point selection - 11 points (it seems like 51 points causes AF to hunt around too much. I am shooting pretty much one subject in the middle of the frame)

AF-C Priority selection - focus + release (a balance of getting things in focus but also shooting quickly, plus a lot of times what it thinks should be in focus is not actually what I want in focus)

Any tips, suggestions, or other resources is also appreciated.


Brian
« Last Edit: September 30, 2008, 09:31:31 PM by bvalente » Logged
Tony Beach
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« Reply #7 on: September 30, 2008, 09:59:27 PM »
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dynamic AF area mode: 51 point 3d tracking (which I assume is for tracking movement, but I really don't know how it relates to AF sensor mode)[a href=\"index.php?act=findpost&pid=225923\"][{POST_SNAPBACK}][/a]

Some birders have suggested that 51 pt. is a good choice, but that it does better without 3D dynamic than it does with it.

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focus tracking with lock on - short (if it loses focus on the subject I want it to find it again fast)


Consider bumping tracking up to Normal.  If you lose the subject just disengage the AF (take your thumb off the AF-ON button) and then reacquire.  Whenever you lose track of what you are trying to focus on, reacquisition that relies on the camera's AF system is hit and miss.
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bvalente
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« Reply #8 on: September 30, 2008, 10:07:57 PM »
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Thanks tony, I'll try out those suggestions


Brian
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bvalente
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« Reply #9 on: October 01, 2008, 11:02:43 PM »
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Tony


Those tips seemed to really help. Where I really noticed was not so much in individual pictures being sharper, but a greater percentage of them being in focus.

Thanks again


Brian
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Tony Beach
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« Reply #10 on: October 01, 2008, 11:55:19 PM »
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Tony
Those tips seemed to really help. Where I really noticed was not so much in individual pictures being sharper, but a greater percentage of them being in focus.

Thanks again
Brian
[a href=\"index.php?act=findpost&pid=226234\"][{POST_SNAPBACK}][/a]

Great, I'm glad it's working for you.  That's a very nice shot you have there.

For sharper images you probably need faster shutter speeds --  just overcoming vibration from the mirror requires a minimum of 1/250.  The shutter speed needs to be increased even more as the subject gets closer, and at really close distances we're probably talking about 1/2000 speeds for fast moving subjects.
« Last Edit: October 01, 2008, 11:55:59 PM by Tony Beach » Logged
Morgan_Moore
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« Reply #11 on: October 03, 2008, 01:48:30 AM »
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Hi Folks,

Lately I've been playing around with both Nikon and Canon camera's (40D and D300).
I'm used to a Canon 5D, which is the camera I use for the most part.

The Nikon D300 and D3 claim to have 51 points, the 40D has 9 points. Both work fantastic in my view. I mostly use manual focus, but it's nice to know it (AF) is there when I need it.

So the question is; is Nikon's 51 point system marketing-bs? Are the 51 points usable or are they just overkill? Since both camera's seem to do just fine, I'm struggeling to see if there is a point in having more AF-points.

regards,

Mike
[a href=\"index.php?act=findpost&pid=189181\"][{POST_SNAPBACK}][/a]

One thing to consider is the max spacing of the dots

The D3 has the same spread as the D300 - ie there is a large gap round the edge of the D3 that is left not covered by AF at all

9 intelligently placed dots would be better than the D3 clusterf*ck

Heres a thought - shooting sport on the $5000 D3 Im going to probably waste 20% of the frame due to cropping,  giving an effective resolution of 9MP,

With my $1000 D90 I will be able to fill the frame giving 12MP

To be fair on the D3 the AF actually works unlike the D200, D80 that I have had

I havnt tested the 90 in anger yet

S
« Last Edit: October 03, 2008, 01:50:10 AM by Morgan_Moore » Logged

Sam Morgan Moore Cornwall
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BernardLanguillier
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« Reply #12 on: October 03, 2008, 02:59:55 AM »
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9 intelligently placed dots would be better than the D3 clusterf*ck
[a href=\"index.php?act=findpost&pid=226506\"][{POST_SNAPBACK}][/a]

I would appear that the current location of the D3 AF focus points is not only the result of a lack of intelligence, but that there are also some technical limitations with having AF points far from the center on a FF body.

DX bodies still have a lot going for them. I would for sure get a D300 for bird photography.

Regards,
Bernard
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A few images online here!
Morgan_Moore
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« Reply #13 on: October 03, 2008, 03:13:39 AM »
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I would appear that the current location of the D3 AF focus points is not only the result of a lack of intelligence, but that there are also some technical limitations with having AF points far from the center on a FF body.

DX bodies still have a lot going for them. I would for sure get a D300 for bird photography.

Regards,
Bernard
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Technology, price of chucking the same unit in multiple bodies, or stupidity - makes no difference to a prospective purchasor why it is like it is

We can only buy the tools that are for sale

To me the big limitation on AF is the lack of ability to program a range into it

Using a 14mm in a water housing the thing creeps to drips on the front of the dome - there are other instances too on land - foreground branches etc

I know range is available on the super teles - but why not as firmware in the camera for all lenses


S
« Last Edit: October 03, 2008, 03:13:58 AM by Morgan_Moore » Logged

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Tony Beach
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« Reply #14 on: October 03, 2008, 11:22:21 AM »
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To me the big limitation on AF is the lack of ability to program a range into it

Using a 14mm in a water housing the thing creeps to drips on the front of the dome - there are other instances too on land - foreground branches etc

I know range is available on the super teles - but why not as firmware in the camera for all lenses[a href=\"index.php?act=findpost&pid=226515\"][{POST_SNAPBACK}][/a]

The purpose of focus limiter switches is not to force focus into a particular range, it is to prevent hunting outside of that range.  The reason a focus limiter feature won't help for the applications you are proposing to use it on is that if the AF wants to lock on to something outside of its range and is prevented from that, then the AF will simply freeze up -- an out of focus branch or drip in the foreground that blocks something you want to focus on behind it will still interfere, which is why you have to sometimes manually override AF.
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bvalente
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« Reply #15 on: October 03, 2008, 09:45:06 PM »
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Tony - after much testing I agree the faster the shutter speed the better. I set my auto ISO at 1/1250 and it's usually higher, shooting wide open on my 400mm f2.8

Thanks again


Brian
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