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05-23-2008, 04:42 PM   #1
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how does multipoint focusing work?

I've used center spot focus almost exclusively since I got my first Pentax DSLR.

Now I'm wondering what the multipoint focusing option does. Why would I use it instead of center spot? How does the camera know what point to focus on?

And would multipoint focusing be FASTER (say, in low light) than center-point focusing?

Will

05-23-2008, 05:33 PM   #2
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Oh goodness. Far faster in low light. Why wouldn't you use center spot? Well, because your subject isn't always in the center! Now, I use the K10D and you can use Selected Focus, or Auto. With the "SEL" option, you pick where you want it to focus, very useful when you are taking time to perfectly compose your shot. When I am doing quick snapshots or sports, I always use auto. It will try and choose the subject you want. Scary enough, it's usually right.
05-23-2008, 06:07 PM   #3
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I for sure could be wrong here... in my experience the multi-point focus system tends strongly to focus on the closest object in the "focusing region". Or if not strictly the closest then the object which bounces the strongest/fastest signal back through the lens. And if the closest/strongest/quickest object is not in focus range the system just stalls out.
Again, this is merely my personal observations when using multi-point. I didn't like the results I was getting from it so switched back to center point and do any additional composition after establishing focus.
05-23-2008, 07:18 PM   #4
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Chris, thanks for the response. Like Venturi, I'm used to locking focus and then recomposing - been doing it so long it seems second nature. So the fact that the focal point isn't always in the middle isn't a problem.

If the multi-point focus really is faster in low light, THAT would be worth knowing. I'm asking largely for that reason. Last night, shooting an elementary school graduation inside a church, I missed quite a few shots because the K20D could not lock focus. I was using center-spot focus, which as I said is about the only thing I've ever used.

I am a bit worried about Venturi's report that the results are iffy. I vaguely recall using it to do some sports shooting, and I did have some odd results, where the wrong player was in focus.

But it might be worth another try...

WP

05-23-2008, 08:17 PM   #5
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Hi Will

Re your question:

QuoteQuote:
I'm wondering what the multipoint focusing option does.
I've tried various combinations with my K10D, but have invariably reverted back to using the centre-spot focussing mode. On those rare occasions that I've bravely ventured out of my comfort zone into the multi-focus mode, I find the bloody camera invariably hunts all over the place like a demented maniac. Sadly I don't have any Pentax lenses to compare with my Tamron, so I can't say whether the problem lies with lack of lens contrast/focal length or something else altogether. PLEASE I BEG YOU ALL, don't lets start yet another Pentax focus-bashing issue thread. It's just that I can't help wondering why other manufactures models appear to work better than the K10D in their respective multi-point focus modes ? Are their algorithms superior to Pentax's ones or is it all a load of old 'auto-focus hocus-pocus' ? Frankly I haven't got the faintest clue, but in my case this setting is pretty much redundant on the K10D. I wouldn't have the slightest hesitation in using multi-point focus if I felt I could trust it implicitly, but I can't so I don't !!!! Luckily my subject matter usually consists of architectural, landscape & general travel photography as opposed to action sports etc, so fortunately speed of focussing is not particularly an issue for me and the superb ergonomic handling and solid build quality of the K10D outweigh these other considerations. FWIW that's my $0.02 cents-worth.....so now it's over to the rest of you !

Best regards
Richard
05-23-2008, 09:46 PM   #6
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QuoteOriginally posted by Confused Quote
I've tried various combinations with my K10D, but have invariably reverted back to using the centre-spot focussing mode. On those rare occasions that I've bravely ventured out of my comfort zone into the multi-focus mode, I find the bloody camera invariably hunts all over the place like a demented maniac.
OK, another testimonial for me to weigh. Thanks.

Clearly, I'm just going to have to give multi-point focus a try and see for myself. Unfortunately I'm so busy with client shoots that I don't have much time to take risks, but I'll have to find some time to do some testing.


QuoteQuote:
PLEASE I BEG YOU ALL, don't lets start yet another Pentax focus-bashing issue thread.
Richard, I assure you that is not my intention in any way here. If I can put it this way without offending anybody, I feel like I'm pretty much stuck with Pentax right now, so to be honest, I almost prefer NOT to hear that any other brand is better. All I want to know now is how to make the most of the Pentax stuff that I've got.

The problems I had at least night's graduation were pretty annoying. A number of things happened somewhat by surprise and I had to aim quickly, and sometimes I had the horrible feeling of pressing the shutter and nothing happening, because the camera wasn't locking focus. That's what has brought me to thinking about multipoint focus as an option. But it's possible that my problems lay elsewhere, starting perhaps with the Sigma 18-50 f/2.8 macro lens that I was using on my K20D; I used to think it was a pretty good lens, but I'm changing my mind about that. I wonder if I would have had those problems if I'd used a Pentax lens instead, say, the 16-45 f/4 or the 35 f/2. Have to test those possibilities, too.

But I'm also looking here for basic illumination on the principle behind multipoint focus. Chris said (in the first reply to my question) about the accuracy of multipoint focus that, "Scary enough, it's usually right." I'm willing to accept that testimonial, too, but I agree - if it's true, then it is a bit scary. I mean, how does the camera know how to pick the true focal point? There must be some logic to it. And I suspect that it's not as simple as "focus on whatever is closest to the camera."

Will
05-23-2008, 10:34 PM   #7
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Just as clarification to my earlier reply. In no way did I intend to imply that the AF system was flawed or "iffy". Multi-point focus just doesn't work for the vast majority of shots I am taking.
I tend to be physically close to my subject and I am idiotically obsessed with DOF. So for example when I'm taking shots of my 7-week old son, who is a constant flurry of hands elbows knees and feet, I'm usually no further then 3 to 5 feet away from him and I don't want the camera to decide that his right elbow is more important than the silly grin on his face.

Having said that if I were shooting predominantly long distance shots (e.g. wildlife or sports) the multi-point system would probably suit me just dandy and save a little bit of composition work while taking shots.

As far as I am concerned though the focusing system is pretty darn spot on - even when I get silly and put the 1.5TC on my slow Tamron 75-300 to *try* and snap a good shot of the moon.
05-24-2008, 12:57 AM   #8
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I've been using multi point selective focus with my K100Ds for since the beggining. It works best for me. Normaly I keep the AF point in the centre, but sometimes I switch it to the other 8 cross type sensors.
As fort the speed. It does matter what lens I use. Outdoor it's OK with all my lenses. But indoor DA40 rules! Remember, the more light you let in for focusing (the bigger apperture your lens has) the faster it works! - to certain point of course...

05-24-2008, 01:58 AM   #9
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I've tried automatic AF-point selection, but I've always found myself going back to centre-point focusing.
I trust my skills more than I do my camera's.

I've also found that using just one focus point at a time increases AF speed; which makes sense, because the camera doesn't have to worry about the entire scene.
05-24-2008, 02:37 AM   #10
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It all depends on the subject. For sport and portrait, I use center spot, but for street use, I'll go "auto" (same for landscape), then there are special occasion like when I'm doing multiple with main subject always in the same area where I'll go to select. The AF is not faster in one mode or the other. The rationale for using "auto" on "street" and landscape is the fact that the auto setting will try to go to the closest or contrastiest object it "sees", which is usually your center of interest in "street" photography and landscape where you want to include a "piece" of foreground as a lead in. For sports, like hockey, the auto setting is just about useless, since it will try to lock on the "clear" screen surrounding the skating rink.
05-24-2008, 03:12 AM   #11
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Hi Venturi

You summed up my thoughts precisely on the K10D's multi-point focus mode when you said:

QuoteQuote:
Multi-point focus just doesn't work for the vast majority of shots I am taking.
I couldn't have put that better myself......I just adore plagiarism.....lol !

Best regards
Richard
05-24-2008, 08:36 PM   #12
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QuoteOriginally posted by WMBP Quote
The problems I had at least night's graduation were pretty annoying. A number of things happened somewhat by surprise and I had to aim quickly, and sometimes I had the horrible feeling of pressing the shutter and nothing happening, because the camera wasn't locking focus. That's what has brought me to thinking about multipoint focus as an option. But it's possible that my problems lay elsewhere, starting perhaps with the Sigma 18-50 f/2.8 macro lens that I was using on my K20D; I used to think it was a pretty good lens, but I'm changing my mind about that. I wonder if I would have had those problems if I'd used a Pentax lens instead, say, the 16-45 f/4 or the 35 f/2. Have to test those possibilities, too.

Will
Will, I have photographed 7 weddings this spring with DA* 16-50 and 50-135 on my k10d. When the lights drop at the reception for dancing, the DA* 16-50 is the fastest to focus of my three main lenses, including the 50-135, FA 31, and FA77. I use center point focussing always.
05-24-2008, 09:54 PM   #13
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QuoteOriginally posted by Wethphotography Quote
Will, I have photographed 7 weddings this spring with DA* 16-50 and 50-135 on my k10d. When the lights drop at the reception for dancing, the DA* 16-50 is the fastest to focus of my three main lenses, including the 50-135, FA 31, and FA77. I use center point focussing always.
Thanks for that input, Erl. I may have to break down and get the Pentax DA* 16-50 to go with the DA* 50-135 that I have already.

I bought the Sigma counterpart (the 18-50 f/2.8 EX DC Macro) shortly before the Pentax DA* 16-50 was released. It seemed to be well regarded and, while it wasn't more than I expect to pay these days, it certainly wasn't cheap, either. I've taken some decent shots with it, but it seems a bit particular about conditions. I've been regretting lately having sold the Tamron 28-75 f/2.8 last year (which I did so I could get the DA* 50-135, ah the joys and strategies of LBA!). Well, good news is that the DA* 16-50 has come down in price a little.

Will
05-25-2008, 05:26 PM   #14
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Yeah I found the multi thing often chose the wrong thing to focus on. I belive the manual, well my old istDs one anyway, said it focussed on the nearest object that fell on one of its 11 spots, not usually what I want to focus on. Sports especially with people running all over the place I want to choose, so centre point it is. I usually just leave it on SEL, then if I have time I select the point, otherwise it's focus and reframe.
05-25-2008, 06:16 PM   #15
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Random observation:

I'm finding that I get a high percentage of missed focus (usually backfocus) with my K10D when I use selected focus point with anything other than the center. (Primarily with my DA 40mm f/2.8 Limited.) I didn't really have the same problem with my K100D. When I tried some simple tests, it seemed to work fine, but even if I'm really extra careful in the field, I come back with a lot of disappointments.

Anyone else seen similar? I'm considering sending it in to have it checked out.
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