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#1
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Pentax istDS slow focus/hunting
I was shooting the kids' soccer game today with the istDS and the 18-55
mm kit lens. I usually use my old manual F4 70-210 zoom, but I wanted to try autofocus. For the most part things went well, but I missed a number of shots because focusing was just too slow. Is this limited by the camere or would another lens autofocus faster? I am looking longingly at the DA* lenses but expect that I would have to upgrade the body as well to take full advantage. Dave -- There's a fine line between stupid and clever. |
#2
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Pentax istDS slow focus/hunting
On Sep 23, 6:45 am, (Dave Devine) wrote:
I was shooting the kids' soccer game today with the istDS and the 18-55 mm kit lens. I usually use my old manual F4 70-210 zoom, but I wanted to try autofocus. For the most part things went well, but I missed a number of shots because focusing was just too slow. Is this limited by the camere or would another lens autofocus faster? I am looking longingly at the DA* lenses but expect that I would have to upgrade the body as well to take full advantage. The DS certainly has slower AF than the K10D, and about equivalent to the K100D. Part of the limiting factor, I think, is the use of AA batteries. You might get better results by using AA Lithium batteries, instead of NiMH. I presume you were using Continuous AF? Mike |
#3
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Pentax istDS slow focus/hunting
"Dave Devine" a écrit dans le message de news:1i4we53.1i38viq1kwjy8tN%dave_devine@nospamcop .net... I was shooting the kids' soccer game today with the istDS and the 18-55 mm kit lens. I usually use my old manual F4 70-210 zoom, but I wanted to try autofocus. For the most part things went well, but I missed a number of shots because focusing was just too slow. Is this limited by the camere or would another lens autofocus faster? I am looking longingly at the DA* lenses but expect that I would have to upgrade the body as well to take full advantage. according to the firsts DA* owners, the SDM motor doesnt add speed to the terrible focus system of the K10D. Maybe with will help the slower AF of your DS |
#4
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Pentax istDS slow focus/hunting
Mike Hamilton wrote:
The DS certainly has slower AF than the K10D, and about equivalent to the K100D. Part of the limiting factor, I think, is the use of AA batteries. You might get better results by using AA Lithium batteries, instead of NiMH. I presume you were using Continuous AF? Mike Thanks Mike, I'll try lithiums. (And yes, I was using the continuous AF). Dave -- There's a fine line between stupid and clever. |
#5
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Pentax istDS slow focus/hunting
Dave Devine wrote:
I was shooting the kids' soccer game today with the istDS and the 18-55 mm kit lens. I usually use my old manual F4 70-210 zoom, but I wanted to try autofocus. For the most part things went well, but I missed a number of shots because focusing was just too slow. Is this limited by the camere or would another lens autofocus faster? I am looking longingly at the DA* lenses but expect that I would have to upgrade the body as well to take full advantage. You wouldn't need a new body for those lenses, but you would miss out on the SDM autofocus feature. As far as autofocus: The biggest contributing factor is the aperture of the lens. The kit lens isn't very fast (in terms of aperture), so it hunts a bit. A faster lens like the FA 50/1.4, or even the DA 16-45/4 do a much better job. -- http://www.xoverboard.com/cartoons/2..._argument.html |
#6
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Pentax istDS slow focus/hunting
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#7
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Pentax istDS slow focus/hunting
On Sun, 23 Sep 2007 07:50:41 -0700, Mike Hamilton wrote:
The DS certainly has slower AF than the K10D, and about equivalent to the K100D. Part of the limiting factor, I think, is the use of AA batteries. You might get better results by using AA Lithium batteries, instead of NiMH. Lithium AA batteries probably wouldn't help. They're designed with a built-in current limiter, and if you want much greater current capability, use NiMH batteries. Even low capacity NiCd batteries will be able to provide much more current than lithium and alkaline batteries, and this is most apparent when using AA batteries in relatively powerful external speedlights. The flash recycle time can be twice as long using lithium AA cells versus using rechargeable AA batteries. Nikon's SB-800 manual states that lithium AA cells have a minimum recycle time of 7.5 seconds, vs. as little as 3.5 seconds for 1,000 mAh NiCd cells and 2.9 seconds for 2,000 NiMh cells. Alkaline AA cells, BTW, are rated at 5 seconds under the same conditions, but the recycle times for alkalines are likely to increase much more quickly as they are used than for the other battery types. Slow focus is usually caused by two things, the first of which is using a lens that is inherently slow, due either to its AF design or because it has a relatively small maximum aperture. The other is having a subject that doesn't provide a very good focusing target. Test the camera by trying to focus on something having clearly defined dark and light vertical or horizontal bars. Trying to focus on quickly moving soccer players is likely to be more difficult. Even the uniform colors can have an effect on focusing performance. As far as cameras go, any kit lens, irrespective of brand is likely to have the poorest focusing performance of the available lenses. Try a lens with a maximum aperture of f/2.8 and you should see a substantial improvement in focusing speed. If you're not too close to the players and can use a very small aperture with the kit lens to maximize depth of field, you might be able to get away with pre-focusing (focus lock, using manual focus, etc.) to completely eliminate AF delay. |
#8
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Pentax istDS slow focus/hunting
On Sat, 29 Sep 2007 11:21:31 -0400, Robert Coe
wrote: What's the rationale for switching to lithiums? Is it that the required current draw may exceed the capacity of anything but lithiums? Or is it that lithiums do a better job of maintaining their target voltage when they're partially discharged? Neither, they're higher voltage (1.8V) when new, makes the simple DC focus motor run faster. The voltage doesn't fall much under load, unlike an alkaline. No theory, lots of users of Pentax cameras have the same practical experience. -- John Bean |
#9
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Pentax istDS slow focus/hunting
On Sat, 29 Sep 2007 13:35:01 -0400, ASAAR
wrote: On Sun, 23 Sep 2007 07:50:41 -0700, Mike Hamilton wrote: The DS certainly has slower AF than the K10D, and about equivalent to the K100D. Part of the limiting factor, I think, is the use of AA batteries. You might get better results by using AA Lithium batteries, instead of NiMH. Lithium AA batteries probably wouldn't help. They do. Higher voltage makes the AF motor run faster. Simple as that - and I know this from experience with my DS :-) -- John Bean |
#10
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Pentax istDS slow focus/hunting
On Sat, 29 Sep 2007 19:03:47 +0100, John Bean wrote:
Lithium AA batteries probably wouldn't help. They do. Higher voltage makes the AF motor run faster. Simple as that - and I know this from experience with my DS :-) Things may not be that simple. If lithiums work better, it's probably because alkalines are run down. With fresh batteries, if there's still a noticeable difference, then the AF was poorly designed, since most people would (or should) use NiMH batteries, which provide even lower voltages. If these batteries that can provide the greatest current (by far) also have the worst AF performance, then Pentax's engineers were unusually incompetent, producing cameras whose design is remarkably flawed. I somehow doubt that this is the case. |
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