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Old Apr 24, 2009, 11:15 AM   #11
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I'd make sure to try out cameras that you want to consider before switching systems.

Pentax dSLR models do tend to lag behind similar models from other manufacturers in areas like AF tracking (where you're shooting a non-stationary subject).

For example, read the "Autofocus Report" section of Dave Etchells' K20D review on this page, where he discussed how frustrating using the K20D was at a rugby game, and how startling the improvement was when he switched to a D80.

http://www.imaging-resource.com/PRODS/K20D/K20DA.HTM

Or, look at this thread in a Pentax forum discussing a magazine test of AF tracking and accuracy:

Magazine Review: K20D/SDM AF.C performance vs. 8 competitors

But, if you're not shooting rapidly moving subjects, the K20D AF shouldn't be as bad as you're describing, unless you're doing something wrong, or the camera settings are not as they should be (and I'd reset your Custom functions to factory defaults), or your expectations are just set too high.

So, I'd try out cameras you're considering before assuming one is going to be faster than another in the conditions you shoot in more often. Also, make sure to consider lens costs (as replacing your lenses with similar models from another manufacturer is not going to be "cheap").

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Old Apr 24, 2009, 11:47 AM   #12
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Dave:

Are you using any filters on your lenses? If so, you may want to remove them and see if camera's behavior changes (in case the filters are causing an issue with how your cameras' AF sensors can "see" to Autofocus).

Also, if you're using the camera's flash for AF assist, that may be causing an issue. I've seen some cameras show much worse Autofocus performance using a built in flash for Autofocus assist, versus focusing with AF assist disabled. ;-)

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Old Apr 24, 2009, 11:53 AM   #13
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thanks jim, most of the times the subject is still, i would like to mention though , that with the 50-135 lens , focus lock is much faster,the problem is very doninant with the 16-50,is it a fact that the wider the lens the harder it it is to focus? or do i have a lens that suffers with issues ever so often

i dont shoot sport photography, just general everyday shots

as far as checking out different systems, i live in the caribbean and we dont have those kind of photooutlets, this is why i am trying to be pointed in the right direction.

i will be in florida next week for a few days, and during that time i have go Miami, Orlando,Daytona and i am trying to fit in Jacksonville, and only 5 days to do this, so if i am going to get a new system, i really wont have time to spend looking at different systems, at this point i would like to know what system to get befor i reach

mind though, i am not asking for you to tell me to buy that one or this one

i would like to know though, if i replaced my K20D with either the Nikon D90 or the canon 50D or canon rebel Ti1, would i be making a footstep foward or backwards



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Old Apr 24, 2009, 12:08 PM   #14
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You really need to judge AF speed with a given camera body on a lens by lens basis.

Some lenses are going to focus faster than others for a variety of reasons. For example, the way a lens is geared internally can make a big difference, as some are geared towards finer focus accuracy versus faster speed (for example, Macro lenses are usually slower to focus). How sharp a given lens is at wide open apertures can impact Autofocus, as can how bright a lens is when you're not shooting in optimum lighting.

Even flare resistance can impact AF speed, and a wider zoom lens is usually more flare prone for a given lens brightness (due to the larger surface area of the front glass). That's one reason I suggested trying your camera without any filters on the lenses and see if behavior changes (that way, you don't have any additional optical elements that could potentially be causing an issue). You'll also want to make sure you use a lens hood to reduce flare related issues, especially in harsher lighting.

The best way to get an idea of AF speed is to read user reviews of lenses you consider. Of course, take them with a "grain of salt" since user expectations and experience level using a variety of lenses can vary a lot. But, you can usually get an idea of AF performance with a given lens if you can find a larger number of users commenting on it.

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Old Apr 24, 2009, 12:32 PM   #15
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will try, especially the part with using the lens hood, something i never use

according to your last paragraph, can i assume it is the speed and quality of the lens, that determins autofocus speed



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Old Apr 24, 2009, 12:54 PM   #16
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Thanks again Jim

i did what you asked, i took off the uv filter, puy on the lens shade ( took some time to find it though ), went out side , tried some shots, came back inside closed all the window blinds, turned off the lights, took some more shots, and i am totally amazed.

i was using a different camera, this cam locked focus the instant my finger touched the shutter button outside and inside , i mean like instant



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Old Apr 24, 2009, 12:57 PM   #17
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dafiryde wrote:
Quote:
i was using a different camera, this cam locked focus the instant my finger touched the shutter button outside and inside , i mean like instant
Dave - figure it would have cost you $1500 minimumto switch systems. I say you take 10% of that - $150 and give it to Jim and call it a day.
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Old Apr 24, 2009, 1:12 PM   #18
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JohnG wrote:
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dafiryde wrote:
Quote:
i was using a different camera, this cam locked focus the instant my finger touched the shutter button outside and inside , i mean like instant
Dave - figure it would have cost you $1500 minimumto switch systems. I say you take 10% of that - $150 and give it to Jim and call it a day.
personally , for what i just acomplished, i dont mind

BTW i am a heavy diesel mechanic by trade, right now i am covered in fuel and oil and contemplating stopping my work to go take some pics :blah:



Dave


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Old Apr 24, 2009, 2:00 PM   #19
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:-)

I'm glad you found the problem. Just to make sure, you may want to test AF performance with the filter on and off a couple of times in various lighting conditions. But, I have seen users report poor Autofocus performance/accuracy using cheap filters before, which is one reason I suggested removing them and seeing if camera behavior changes.

Anytime you add additional glass (or plastic with some cheap filters), you risk degrading optical performance and increase the potential for flare related problems. Your AF sensors need to be able to "see" well to Autofocus. ;-)

As for a hood, I'd suggest that you always use one, unless it's going to interfere with your flash and cast a shadow. Sometimes, I'll even use one arm to help shade a lens if a given hood isn't doing the job well enough, or even move so that I'm under some shade while shooting if the light is bad enough (i.e., I'm shooting more towards the sun).

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Old Apr 24, 2009, 4:57 PM   #20
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thanks again, i did put back on the filter after and once again the problem came back, so i am convinced it was the filter causing thistrama all this time. i would have never thought of it, as i had put out the extra $ for this filter when i bought the 16-50 which is a Hoya pro 1 digital 77mm mc uv(0) and the Hoya pro 1 digital 77mm mc pl-c

can you recomend a replacement or should i just shoot without them.



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