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.

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

"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

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.

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

On Sun, 23 Sep 2007 19:08:43 +0200, (Dave Devine)
wrote:
: 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).

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? I suspect it's the latter, in which case you could test
the performance of the AF system with a set of new alkalines before spending
the money for lithiums. If new alkalines don't solve the problem, lithiums
probably won't either.

Bob

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.

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

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

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.