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Photo Forum / Digital Photography / DSLR Cameras / September 2007Pentax 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  SignatureThere's a fine line between stupid and clever. > 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 [quoted text clipped - 3 lines] > 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 > 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 [quoted text clipped - 4 lines] > > Mike Thanks Mike, I'll try lithiums. (And yes, I was using the continuous AF). Dave SignatureThere's a fine line between stupid and clever. : > 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 [quoted text clipped - 7 lines] : 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 >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. SignatureJohn Bean > 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. >> 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 :-) SignatureJohn Bean >> 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. >>> Lithium AA batteries probably wouldn't help. >> [quoted text clipped - 4 lines] > Things may not be that simple. If lithiums work better, it's >probably because alkalines are run down. No, it's because the camera was designed to work with a pair of lithium CR-V3s, all AA options are sub-optimal by comparison but AA lithiums come close to the performance of CR-V3s and are somewhat cheaper. Personally I use hybrid NiMH because the AF is fast enough for my purposes, but it is noticeably "snappier" with lithiums. Like it or not, that's the way it is. I've explained the options to get the best AF speed, and the reason lithiums work best. Excuse me for snipping all the derogatory stuff about Pentax designer's competence, that's not actually the issue here since the camera is now obsolete anyway. SignatureJohn Bean > > Things may not be that simple. If lithiums work better, it's > >probably because alkalines are run down. [quoted text clipped - 13 lines] > about Pentax designer's competence, that's not actually the > issue here since the camera is now obsolete anyway. In that case, like it or not, the Pentax designers were incompetent, deciding to produce a camera that requires the use of fairly expensive 'one use' batteries to get decent performance. Whether the camera is obsolete or not has nothing to do with the issue. A poor design is a poor design. My Powershot S10 and S20 came packed with only a lithium battery in their boxes. The optional rechargeable batteries that I bought for them did *not* reduce performance. If that had been the case, I would have been very annoyed with Canon and probably would not have purchased several more of their cameras. It also would have meant that the cost of using the one-use batteries for several years might have approached the cost of these quite expensive P&S cameras. That Pentax's designers though less of their customers should be taken into consideration by all future owners, since future cameras can't be automatically assumed to be free of similar 'issues'. That doesn't mean that future Pentax cameras won't be excellent products, but it does mean that unless there's a good reason why the Pentax corporate culture has changed, prospective buyers need to be wary. It's no different with other manufacturers. For several years, alert Canon owners have been aware that buyers of new models are occasionally (unfortunately) treated by Canon as beta testers. Sometimes they get bitten, other times there's been no problem with new models. All of the Canon cameras I've bought in recent years have been after they've been available for a long enough time for the dust to settle. Ask some of Canon's Mk III early adopters if they're feeling as much joy today as they did when they ordered their latest beta product. >> > Things may not be that simple. If lithiums work better, it's >> >probably because alkalines are run down. [quoted text clipped - 15 lines] > > In that case [...] Whatever, I didn't read it. The question was about whether lithiom batteries make focusing faster on a DS. They do. End of. SignatureJohn Bean > Whatever, I didn't read it. The question was about whether > lithiom batteries make focusing faster on a DS. > > They do. End of. Thanks for confirming that you're an unadulterated twit. <EOT> > 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 [quoted text clipped - 3 lines] > 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 > 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 [quoted text clipped - 3 lines] > 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. Signaturehttp://www.xoverboard.com/cartoons/2007/070416_argument.html > > 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 [quoted text clipped - 13 lines] > > --http://www.xoverboard.com/cartoons/2007/070416_argument.html Yes a faster lens will help. I'm not familar with that camera, but also make sure you have only 1 focus point turned on. If you have multiple ones turned on, the camera will go back and forth between focus points as players move around. |
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