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03-01-2010, 07:57 PM   #1
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multi-point (11, 16, whatever) focal system—WHY??

Camera makers seem to boast about the number of focus points in their system. 9's no good, you gotta have 11. But then 11's no good, you gotta have more. I think somebody has 64. (Perhaps I'm making that up.)

What's the point of all those focus points? DO I need more than one? Occasionally I do like to move that one around. Is that the point?

I've wondered about this for a long time and thought I would finally ask.

Will

03-01-2010, 08:10 PM   #2
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More points allow you to compose and focus rather than focus and compose.
In the more sophisticated systems, the AF can be set to track an object that is moving from point to point. The AF will "hand off" the subject from one point to another, so that as long as the subject can be tracked, focus will be maintained (think of how handy that would be for photographing birds in flight).
03-01-2010, 08:21 PM   #3
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Thanks for the quick reply, Wheatfield.

QuoteOriginally posted by Wheatfield Quote
More points allow you to compose and focus rather than focus and compose.
I can understand that. Occasionally when I compose and focus I do wish I had more points to work with.


QuoteQuote:
In the more sophisticated systems, the AF can be set to track an object that is moving from point to point. The AF will "hand off" the subject from one point to another, so that as long as the subject can be tracked, focus will be maintained (think of how handy that would be for photographing birds in flight).
This is where I get lost.

Does this feature work only when you have the focus set to autopoint AND the focus method set to continuous focus?

What happens if I'm shooting a flock of birds—say, a dozen or so seagulls flying around above me? How does the system know what focus point it should use?

Somehow, I thought that the purpose of these 47 focus points or whatever was to improve autofocus when you had it set to autopoint.

Should I be using auto-point autofocus? I use center-point, most of the time, unless I'm doing a portrait, am close to my subject, and am worrying that focus and recompose will cause me a problem. Then I will switch to select-a-point focus, select my point and focus, then shoot.

Will
03-01-2010, 11:07 PM   #4
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QuoteOriginally posted by WMBP Quote
Thanks for the quick reply, Wheatfield.



I can understand that. Occasionally when I compose and focus I do wish I had more points to work with.






Does this feature work only when you have the focus set to autopoint AND the focus method set to continuous focus?
No -- it's probably more useful in AF C, but it automatically will choose a focus point in AF S.

QuoteQuote:
What happens if I'm shooting a flock of birds—say, a dozen or so seagulls flying around above me? How does the system know what focus point it should use?
I believe the AF system will choose the closest contrast area to focus on. It's not like it can read your mind -- and that's why I only use it when shooting a quickly moving object that my less than optimal technique can't keep centered in the VF.

QuoteQuote:
Somehow, I thought that the purpose of these 47 focus points or whatever was to improve autofocus when you had it set to autopoint.
It does -- or should -- consider what would happen if you doubled the number of AF sensors. The total area covered by all the sensors would probably remain the same (kinda like the Chevy "bowtie", except straight) -- so each AF sensor would now cover about 1/2 the area. Smaller sensors would allow more discreet contrast detection which would theoretically give you better AF accuracy by eliminating some possible sources of unintended AF lock. An AF sensor will lock on the strongest contrast border within the sensor's area -- preferring either vertical or horizontal contrast borders, so if you were shooting a person standing in front of a white picket fence, for example -- the AF sensor might choose the fence if part of it were to be included in the sensor's area because the contrast borders are straight vertical and have more contrast, and the person overall will tend to present less contrast and won't have equally strong straight vertical or horizontal contrast borders.

QuoteQuote:
Should I be using auto-point autofocus? I use center-point, most of the time, unless I'm doing a portrait, am close to my subject, and am worrying that focus and recompose will cause me a problem. Then I will switch to select-a-point focus, select my point and focus, then shoot.
That's your choice, but most photographers prefer to choose what they want to be in critical focus. For me, multipoint works better for moving subjects using AF C -- it's a hedge against my inability to track with accuracy when looking through the VF. For most of my shooting (birds primarily), I use AF S and center point focusing. I completely agree with your choices of center point and select point with the current system.

Bottom line, 11 point AF in SAFOX VIII+ works well, but I'd like to see an upgrade of the current system to more sensors, and algorithms that allow for even better tracking. In the K-7, it's demonstrably better than previous bodies, but a bit behind some of the competition.

Scott

03-02-2010, 05:54 AM   #5
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I think a lot depends on what you are shooting. If you are generally shooting portraits or landscape, you can probably get by with even 6 or 7 autofocus points. As Wheatfield says, they are useful so that you don't have to shift your camera after achieving focus.

The large number of focus points is useful for tracking moving objects. My understanding is that Nikon has predictive focus that once you lock focus, the camera will keep the object in focus, or at least attempt to. I think that you can turn some of them off, depending on what you are shooting as well.

I like where Pentax has their focus points placed -- I use focus point select all of the time and it helps me to think about where I want to place my subject. When I first started taking photos, you could have put a bull's eye on my photos in the exact center and that's where they would be, but nothing wrong with center point and recomposing either.
03-02-2010, 06:42 AM   #6
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One other advantage i guess is when you are using a tripod at night is pretty hard if you have limited focus point the lens keeps on hunting, so with more focus point you dont have to focus and recompose. The tripod and the camera stays steady and you can select either auto or select a focus point where there is light..
03-02-2010, 07:12 AM   #7
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I shoot Canon, and the ONLY reason ANYONE should EVER use "Auto-select" is when using AI-Servo (~AF-C in Pentax-speak) When you activate the focusing, the system initially grabs focus using the CENTER point. As you track the subject, if the subject moves from the center point, it will "hand off" to the other points (I believe Wheatfield mentioned this)

But what I'm adding to the discussion is that the CENTER point is used initially.

For One-shot (AF-S), AUTO-select should NOT be used if you care one inkling about where the camera should focus. You should ALWAYS be explicitly chosing your focus point. The more focus points to chose from, the less need for focus-recompose (which can lead to focus errors when using wide apertures at close distances)

My 40D has a neat "joystick" which makes selecting the AF-point pretty easy.
03-02-2010, 07:45 AM   #8
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QuoteOriginally posted by egordon99 Quote
I shoot Canon, and the ONLY reason ANYONE should EVER use "Auto-select" is when using AI-Servo (~AF-C in Pentax-speak)
AFAIK, this is the same in the Nikon system. The extra 50-60 focus points are purely to make their AF-C equivalent work better so it'll actually track movement. They have gazillions of menu settings for it to work right for different subjects too...

What I really wish is that Pentax would leave their focus indicators lit up like other makers do...it'd help if you want to keep the focus point on a moving subject...

03-02-2010, 09:09 AM   #9
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QuoteOriginally posted by kenyee Quote
AFAIK, this is the same in the Nikon system. The extra 50-60 focus points are purely to make their AF-C equivalent work better so it'll actually track movement. They have gazillions of menu settings for it to work right for different subjects too...

What I really wish is that Pentax would leave their focus indicators lit up like other makers do...it'd help if you want to keep the focus point on a moving subject...
I personally find that one of the most annoying features of Canons. Very distracting to be trying to shoot a photograph and have blinking lights all over the place in your view finder. Fortunately, they allow you to turn it off.
03-02-2010, 09:29 AM   #10
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Thanks for the responses to my original post. ON the basis of your responses, I've concluded that I'm not missing much having only eleven focus points on my K20D and K10D.

As I said, I generally keep it set to the center focus point. I switch to select-focus point only when I'm shooting portraits, using a wide aperture with shallow depth of field, and standing close enough to the subject that I'm worried that focus-and-recompose might cause the focal plane to move when I recompose. Which is often enough that I'm glad to have the select-option, but perhaps no more than 5% of my shooting, if that. Now, when I'm using select-point focus, there are times when I wish I had an extra point or two, because sometimes I can't get the red blinker right on the spot that I think is key—so I have to do a slight focus and recompose after all, and that can be tricky if the camera's on a tripod. On the other hand, if there were too many focus points, well, moving the selection would take more time. I mean, I can move the focus point around pretty quickly now, because there are so few points to move to. If there were four times as many, I'm not sure I'd like that.

I almost never use continuous focus (AF-C). I've tried it occasionally. Just never got the hang of it. And I've only used auto-point focus a couple of times, as a test. I'm trying hard to control every other aspect of the photo; so it seems odd to let the camera decide what to focus on. I'm sure this would be useful for many other perhaps but it's not for me.

By the way, I checked out the specs for a few other cameras at DPREview.com and in retrospect, I am not sure what I was worried about. Looks like the K-7, as well as the Canon 50D and the Nikon D90, all have only 11 focus points. No, the Canon 50D has only 9 (which I still don't consider a problem). The Nikon D3x—a full-frame camera—gives you a choice, apparently: 51 focus points, or you can switch to only 11. Looks like a lot of photographers have weighed in with the opinion that 11 is about right for most shots. I concur.

Anyway, thanks all. You've satisfied my curiosity.

Will
03-02-2010, 10:15 AM   #11
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Hi, Will, great question and great answers from all. I am going to ask one more question perhaps related to this focus points. If I set the camera to auto-focus point select, does the camera select multipoints to focus and then determine the optimal aperture to ensure everything within the "selected focus points" are in focus?

I look at the EXIF of pictures taken from one of my relativea who uses a Canon 5D. I was never able to determine where the focus is locked on from his pictures. Hence the pictures from him always look flat to me. Is it the camera or did he relies too much on the auto mode of the camera? Or it could be lens..
03-02-2010, 10:24 AM   #12
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QuoteOriginally posted by aleonx3 Quote
Hi, Will, great question and great answers from all. I am going to ask one more question perhaps related to this focus points. If I set the camera to auto-focus point select, does the camera select multipoints to focus and then determine the optimal aperture to ensure everything within the "selected focus points" are in focus?
Canon has a A-dep mode, which is supposed to do something similar, but most Canonites (myself included) generally avoid it.

In reality, there can really only be ONE distance that the lens if focused to. So your best bet is to select only ONE focus point.

When using "All Focus Points", Canon just choses the CLOSEST contrasty object covered by one of the focus points, so it's really a cr*pshoot as to where it is going to focus. In AUTO/Green box mode, you have NO control over this, so I generally tell folks to avoid AUTO mode.
03-02-2010, 10:39 AM   #13
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QuoteOriginally posted by egordon99 Quote
Canon has a A-dep mode, which is supposed to do something similar, but most Canonites (myself included) generally avoid it.

In reality, there can really only be ONE distance that the lens if focused to. So your best bet is to select only ONE focus point.

When using "All Focus Points", Canon just choses the CLOSEST contrasty object covered by one of the focus points, so it's really a cr*pshoot as to where it is going to focus. In AUTO/Green box mode, you have NO control over this, so I generally tell folks to avoid AUTO mode.
Thanks, egordon99 - good to know since I am not too familiar with C line of camera functions. As you said, there should really be one focus point selected by the camera, but how come the EXIF (PhotoME) data was unable to show that? I don't want to hurt his feeling by telling him to use select-focus instead of auto-select because he thinks the Canon 5D MKII can do everything intelligently than my K10D can. And he has been doing that for years (the Rebel series) before I got my K10D a couple of years ago.
03-02-2010, 10:47 AM   #14
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Only Digital Photo Professional (DPP) can display what focus point was used. I think this might not work IF you used "All Focus Points". I don't know because I never use "All Focus Points", and I don't use DPP, I use Lightroom

Regardless, the thought of using a 5DII in AUTO makes me sad
03-02-2010, 10:50 AM   #15
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QuoteOriginally posted by aleonx3 Quote
Hi, Will, great question and great answers from all. I am going to ask one more question perhaps related to this focus points. If I set the camera to auto-focus point select, does the camera select multipoints to focus and then determine the optimal aperture to ensure everything within the "selected focus points" are in focus?

I look at the EXIF of pictures taken from one of my relativea who uses a Canon 5D. I was never able to determine where the focus is locked on from his pictures. Hence the pictures from him always look flat to me. Is it the camera or did he relies too much on the auto mode of the camera? Or it could be lens..
I'm not sure what might be wrong (if anything) with your friend's photos from the 5D. I've seen some great photos taken with that camera, although probably most of them weren't taken with the focus set to auto-select point.

As for your first question above, the way I understand it—which I'm going to state here so somebody who actually KNOWS can correct me—is that the camera has a kind of database built into its firmware that helps it analyze the scene's contrast and make a smart guess about where to focus. I don't think it simply looks for the most contrasty point in the photo and decides, "Let's focus there." I suspect that, for a lot of photographers, auto-select point focus might be fine. Might be fine for many of my own photos, in fact. I liked the comment somebody else made here about how you could draw a bull's eye on his photos because the focus was always smack dab in the center. I've been doing this a long time and I don't always compose my shots with the focus in the center—but I like symmetry and classic composition, and I'd bet that the focal plane in my shots is at or near the center at least 50% of the time. The problem is that other 50%. If you're going to take responsibility for it—and I do that partly by focusing with the AF button rather than half-shutter press—then you might as well take responsibility all of the time. After all, when it's easy, it's easy. And when it's a little harder, it's still easier not to have to switch out of "easy mode" (as it were).

*

This issue has arisen for me because I've been reconsidering (once again) my modus operandi.

For a long time, I shot mostly in M mode, but I had focus tied to the shutter button, because, to be honest, I wasn't aware that there was an alternative for auto-focus. I learned here how to use the AF button, disconnected autofocus from the shutter and haven't looked back.

But I did change my exposure mode after I discovered the power of hyperprogram (P) mode on the K10D/K20D: it lets me access effective Av or Tv mode quickly simply by moving the rear or front e-dial, and by using the +/- (exposure compensation) button, lets me control what the camera is doing just about as well as M mode does. It took me a while to get used to using P this way, mainly because I found it hard to think in terms of +/- EC, having been used to looking at the meter's gauge. Once I got used to P, however, I liked it. A lot. Actually I thought it was brilliant.

And now I'm going back to M again, or so it seems. This time, I haven't made a conscious decision about it. It just seems to be happening. It's partly because I want to be in M when using flash, and I shoot with flash a lot. If I'm shooting with off-camera flash, I have to be in M. And while the exposure mode system really works quite differently with flash than it does with available light, nevertheless, I have been finding it easier to just stay in M all the time, whether I am using flash or not. I think that I must establish a habitual M.O. and then stick with it. If I have to worry about shutter speed some of the time (when shooting M) and not at other times (when using P as effective Av), well, I'll end up forgetting about shutter speed one day when I should not. It's already happened.

I'd love to have the camera do any part of the job automatically, if I could trust the camera to do it the way I want. But I can't, not with exposure. I asked my question here in this thread because I was wondering if perhaps I could make focusing easier. Guess not.

Will
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