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11-02-2007, 12:04 PM   #1
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why use selective focus?

I'm wondering about some of the focusing and exposure options that I've never used and have a couple of little questions. I'm using a K10D. I have a couple other questions but will post them in a separate thread.

Does anybody really use selective auto-focus? When and why do you use it?

I understand what the user's guide says: if you were photographing a girl standing in a garden near a bird bath with a big rose bush off to the other side, you could use selective auto-focus to focus on the girl, or move it to the right and focus on the bird bath, or move it to the left to focus on the rose bush.

But it seems to me much easier to use spot focusing, move the camera so the desired point of focus is in the center of the camera, lock the focus, and recompose. Even the user's guide mentions this -- for when the desired point of focus is outside the 11 focus points. The only situation I can think of in which using selective auto-focus makes practical sense is when the camera is mounted carefully on a tripod and you can't or don't want to move the camera. Is that a situation that anybody actually encounters? Is there another, different reason to prefer selective auto-focus?

Will

11-02-2007, 12:17 PM   #2
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I use it at wide apertures when my subject is close, so that the subject stays in focus. With very thin DOF, recomposing changes the focal plane slightly and there is a greater chance of the camera moving backward or forward, leaving the subject out of focus.
11-02-2007, 12:27 PM   #3
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I have used it from time to time when I am shooting several shots with the subject deliberately off center. Usually however i sue the center spot
11-02-2007, 12:35 PM   #4
and
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Exactly as mentioned, when you are at an angle, recomposing can change the focus if you have thin dof. its quick to change anyways, so I always leave mine in SEL. the focus point cluster is prtty centered though, so often you still have to recompose.

11-02-2007, 01:45 PM   #5
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Oh, another thing. I always leave it on selective focus, and usually just keep it on the center spot and use the "focus-recompose" method. I set the OK button to recenter the AF spot, so if I do use a different AF point, it is easy to center it again.
11-02-2007, 01:50 PM   #6
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Lowell and Andreas,

Just to confirm that I understand what you guys are saying....

Say I'm in an art museum. I've got my Sigma 10-20 with me and I'm in a very small gallery, so I can't step back very far. I'm standing near the door to the next gallery and there's a woman in that next gallery that I'd like to include in a photo -- I'm going to shoot through the door. But I want her out of focus, and I want the focus to be in on the painting hanging in my gallery, to the right of the door. I'm using f/2.8 because I'm not allowed to use flash in the museum. (Well, the 10-20 doesn't go to f/2.8 but never mind about that....) So the woman is at the apex of a right triangle, I'm at one end of the hypotenuse and the painting is at the other end. You're saying that you'd use selective focus here because if you aimed the camera at the painting and locked the focus, then moved the camera back to the left to include the woman in the next room, the painting would now be out of focus. Is that about it?

Does this happen to you often? I mean, the focal length has to be pretty wide and the point you want to focus on really has to way, way off to the side of the composition for this to matter, no?

But this raises an interesting question. Is the focal plane truly a plane? Or is it a concave curve?

Will
11-02-2007, 01:56 PM   #7
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QuoteOriginally posted by Finn Quote
Oh, another thing. I always leave it on selective focus, and usually just keep it on the center spot and use the "focus-recompose" method. I set the OK button to recenter the AF spot, so if I do use a different AF point, it is easy to center it again.
Finn,

You're not the first person I've heard say they do that. I gave it a try -- but I had a problem. I think my big nose must have banged the four-way selector from time to time, because the focus point started moving around on me without my permission. So now I keep it on center-point focusing all the time instead.

In re my big nose, I have to confess that adjust the focus point when using selective focus is difficult. I can't see what's in the viewfinder without having my face jammed up against the back of the camera. But if my face is jammed up against the back of the camera, I can't get my thumb to the four-way selection button very easily.

Will
11-02-2007, 02:05 PM   #8
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QuoteOriginally posted by WMBP Quote
Lowell and Andreas,

Just to confirm that I understand what you guys are saying....

Say I'm in an art museum. I've got my Sigma 10-20 with me and I'm in a very small gallery, so I can't step back very far. I'm standing near the door to the next gallery and there's a woman in that next gallery that I'd like to include in a photo -- I'm going to shoot through the door. But I want her out of focus, and I want the focus to be in on the painting hanging in my gallery, to the right of the door. I'm using f/2.8 because I'm not allowed to use flash in the museum. (Well, the 10-20 doesn't go to f/2.8 but never mind about that....) So the woman is at the apex of a right triangle, I'm at one end of the hypotenuse and the painting is at the other end. You're saying that you'd use selective focus here because if you aimed the camera at the painting and locked the focus, then moved the camera back to the left to include the woman in the next room, the painting would now be out of focus. Is that about it?

Does this happen to you often? I mean, the focal length has to be pretty wide and the point you want to focus on really has to way, way off to the side of the composition for this to matter, no?

But this raises an interesting question. Is the focal plane truly a plane? Or is it a concave curve?

Will
will
sounds like me in paris this summer

I think the only true flat field lenses are macro's. They are specifically designed that way.

11-02-2007, 02:31 PM   #9
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There's also the scenario where the camera's on a tripod, the shot composed and you just need to select a focus point. I shoot miniture scenes frequently and use selective focusing quite often.
11-02-2007, 02:35 PM   #10
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True the plane is often not truly flat. Then again if I want to use anything longer then 50 and less than 300, well then its going to be my 100 macro
11-02-2007, 03:18 PM   #11
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QuoteOriginally posted by WMBP Quote
Does this happen to you often? I mean, the focal length has to be pretty wide and the point you want to focus on really has to way, way off to the side of the composition for this to matter, no?
Well, yeah, basically. I usually notice it the most taking portraits indoors wider than about f/2. If I'm really close to my subject and turn only slightly, it will come out of the focal "plane". It might work ok if I pivoted my body around the end of the lens, but that is way too much work.

Then again, for 90% of my shots it doesn't matter in the slightest. I mean, everyone does the focus-recompose thing with a split prism or a rangefinder. Even my AF film body (a ZX-30) only has a single center AF point. In the grand scheme of things, it's pretty minor.
11-02-2007, 04:56 PM   #12
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I use selective focus all the time - nearly every image. To repeat my self - I have de-coupled AF from the shutter button on both the K10D and the *ist Ds. Rarely do I have the main subject - dead center - in the frame, it's called composition, which I prefer to do when shooting and not during the PP phase. I always use the center focus point also. Why? It is the same mechanism that I used on my manual - split image - focus film SLR's that I have used since the very early 70's. Old habits die hard, I used to shoot sildes almost exclusively, so I had to compose the image in the camera - otherwise the 10 foot wide picture looked --- just plain bad.

Only when I am shooting something that is at is pretty far away from me do I just focus at the center point. Although I have been known to focus on something close and adjust the DOF to include objects in the background. Ah -- the good old days, when you could actually see the DOF engraved on the lens. Back when the only computer associated with the camera was the one behind the viewfinder - when you had to "think" not just blast away and blame the camera for not getting "the" image.

The first AF SLR was a SF-1 - the single most frustrating thing about it is, I still have it, the stupid coupling of the AF and the shutter button. I lost quite a few shots with that thing since every time I pressed the shutter button the focus point (only one and dead center) would hunt for what "it" thought should be in focus.

The Elitiest - Formerly known as PDL

Last edited by PDL; 11-02-2007 at 04:57 PM. Reason: punctuation & spelling
11-02-2007, 05:29 PM   #13
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Interesting response, PDL.


QuoteOriginally posted by PDL Quote
I use selective focus all the time - nearly every image. To repeat my self - I have de-coupled AF from the shutter button on both the K10D and the *ist Ds. Rarely do I have the main subject - dead center - in the frame, it's called composition, which I prefer to do when shooting and not during the PP phase.
I agree that composition is something that one should always try to do at the time of shooting, if for no other reason than that it's a waste of pixels to rely too much on cropping.

But we have more than two choices here, no? I mean, it's not a simple choice between using selective focusing while shooting, OR shooting subjects that are always in the dead middle of the frame and perhaps cropping later to make the picture interesting. You can focus and recompose, it's easy to do, and even with selective focus, you HAVE to do it sometimes, because there are only 11 points and as somebody else already mentioned, they're kinda bunched in the middle of the frame.


QuoteQuote:
I always use the center focus point also. Why? It is the same mechanism that I used on my manual - split image - focus film SLR's that I have used since the very early 70's. Old habits die hard, I used to shoot sildes almost exclusively, so I had to compose the image in the camera - otherwise the 10 foot wide picture looked --- just plain bad.
But now I'm confused. If you always use the center point, then how is that different from using center-spot focusing?

And those old split-image focusing screens -- which I also miss -- required that that subject you were focusing on be in the middle of the frame, because that's where the image was split. So back then, your only choice was to focus and recompose. That experience is in my own background and may have something to do with my asking now, what's the point of selective focusing?

Let me say for the sake of clarity: I'm not asking why anybody would ever want to focus on something that isn't in the middle of the photo. I'm simply asking why you'd need the selective focus option to do that. A couple good answers have been provided now (although they involve doing things that I just don't do very often).

One more point about composition and selective focusing. I shoot a lot of sports, as well as other events where I don't have much time to get arty about the focus and composition. When I see a nice opportunity to focus off-center and put shallow depth of field to good use, I'll take it if I have time. But I often don't have time. I've tried shooting volleyball using AUTO option for AF focusing. The user's guide says about this option that it "selects the optimum AF point even if the subject is off-center." But the camera's idea of "optimum" often turns out to be different from my own. ;-)


QuoteQuote:
Only when I am shooting something that is at is pretty far away from me do I just focus at the center point. Although I have been known to focus on something close and adjust the DOF to include objects in the background. Ah -- the good old days, when you could actually see the DOF engraved on the lens. Back when the only computer associated with the camera was the one behind the viewfinder - when you had to "think" not just blast away and blame the camera for not getting "the" image.
I remember those days myself. I remember when I had to guess the metering on everything because I didn't usually have a light meter with me. I took even more lousy photos back then than I do today. ;-)

Will
11-02-2007, 06:09 PM   #14
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QuoteOriginally posted by WMBP Quote
I agree that composition is something that one should always try to do at the time of shooting, if for no other reason than that it's a waste of pixels to rely too much on cropping.
Composition is of primary concern all the time – wasting pixels – what’s that?

QuoteOriginally posted by WMBP Quote
But we have more than two choices here, no? I mean, it's not a simple choice between using selective focusing while shooting, OR shooting subjects that are always in the dead middle of the frame and perhaps cropping later to make the picture interesting. You can focus and recompose, it's easy to do, and even with selective focus, you HAVE to do it sometimes, because there are only 11 points and as somebody else already mentioned, they're kinda bunched in the middle of the frame.

But now I'm confused. If you always use the center point, then how is that different from using center-spot focusing?
There are some times when the subject of the image spans the “center of the frame” or that no matter how hard we try – it has to be dead centered. But let me state this a little differently – I do not care how many “focus points” you have – I always use the center – when I push the shutter button to get ready to – set the exposure or take the image – the focus does not change. I do not use the “other 10” because I control what is in focus, not the computer in the camera. Your mileage will vary.

QuoteOriginally posted by WMBP Quote
And those old split-image focusing screens -- which I also miss -- required that that subject you were focusing on be in the middle of the frame, because that's where the image was split. So back then, your only choice was to focus and recompose. That experience is in my own background and may have something to do with my asking now, what's the point of selective focusing?
Well, if by the term selective focus – using focus points other that the center, then my experience with it is less than satisfying. For example, I was shooting my son’s graduation (long before I knew a lot about using manual lenses and getting rid of the shutter/focus debacle) – one image he is in focus – next image the back of the head of the guy in the seat in front of me is in focus – next image my son is in focus. Lose the machine, take control.

QuoteOriginally posted by WMBP Quote
snip
One more point about composition and selective focusing. I shoot a lot of sports, as well as other events where I don't have much time to get arty about the focus and composition. When I see a nice opportunity to focus off-center and put shallow depth of field to good use, I'll take it if I have time. But I often don't have time. I've tried shooting volleyball using AUTO option for AF focusing. The user's guide says about this option that it "selects the optimum AF point even if the subject is off-center." But the camera's idea of "optimum" often turns out to be different from my own. ;-)
I can not comment about taking sports – I do not shoot sports per se. I did shoot some cricket in NZ last year, but with a 300mm manual lens – I just focused on the wickets and let the subjects move into focus (the lens had a DOF scale I was shooting at f/8.0 at about 50 meters so the DOF was reasonably deep). It worked well, but I did not go to a baseball game this year where that would be the next area to “try my theories”.


QuoteOriginally posted by WMBP Quote
I remember those days myself. I remember when I had to guess the metering on everything because I didn't usually have a light meter with me. I took even more lousy photos back then than I do today. ;-)

Will
The light meter in my SLR’s worked just fine – once I got used to their peculiarities. The problem was behind the camera. I find that now I take many more iffy/questionable/cr*ppy images. I guess it is too easy to just take more rather than getting it right by thinking. With sports it all comes down to being intimate with the subject and anticipating/knowing where the next best shot is. Before digital, AF, auto winders and motor drives were around – there were some spectacular sports pictures taken. I think I am using the ease of multiple shots to cover my lack of attention to the fundamentals.

The Elitist – formerly known as PDL

Last edited by PDL; 11-02-2007 at 06:11 PM. Reason: spelling
11-02-2007, 09:48 PM   #15
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QuoteQuote:
Well, if by the term selective focus – using focus points other that the center, then my experience with it is less than satisfying. For example, I was shooting my son’s graduation (long before I knew a lot about using manual lenses and getting rid of the shutter/focus debacle) – one image he is in focus – next image the back of the head of the guy in the seat in front of me is in focus – next image my son is in focus. Lose the machine, take control.
PDL,

You lose me completely here.

I didn't start this thread to ask a grand question about whether it's good or bad for the photographer to be in control (it's good, we agree about that) or whether composition is important in photography (we agree about that, too). I started the thread to ask a simple technical question about the practical value of the selective focus option. Selective focus is not a vague term. It does not mean "using focus points other than the center." It refers to one of the three methods that the K10D gives us for controlling auto-focus. Selective focus is achieved by using the AF point switching dial that encircles the four-way controller. Turn the AF point switching dial to SEL, and you're using selective focus, whether you use the center point or one of the other ten points.

But I asked you, if you ONLY AND ALWAYS use the center point in SEL focus, then what is the difference between using selective focus and using center-spot focus -- one of the other three auto-focus options? I don't think you answered this question.

Will
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