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08-16-2010, 01:37 AM   #1
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focusing problems on k-x

hi all
have just bought my first dslr - pentax k-x and 18-50mm lens bundle
Having problems on focusing where the lens seems to take an age to focus - it drives in and then drives back out again - Do I have a setting wrong ?
Appreciate the help as I am a true noob !

08-16-2010, 01:57 AM - 1 Like   #2
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Are you using the live view mode where your picture shows up on the LCD screen full time? it sounds like you are

Because if so the default focus method in live view is super slow and you can simply change it in the settings, It's been a while since I sold my Kx so I can't remember exactly how. I'm sure someone else can outline the procedure for you

If you are looking through the viewfinder and are having problems, that just means the AF system can't handle the conditions, if it's too dark or you're trying to focus on an object that is one plain color and has no detail, then chances are the AF system just wont work and you'll have to use manual focus

to me it sounds like you're using live view for sure and there's a simple fix in the settings, it should be in the manual, you can try checking if there's a live view or focus mode section in the manual, I really wish I can remember exactly how to do it on the Kx but I know it's just a simple setting
08-16-2010, 02:23 AM   #3
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thanks for the feedback future -
I am getting the problem with both - so will look through manual for the LV problem -

Will experiment with what I am focusing on to see if it is the conditions

Once again thanks for feedback
08-16-2010, 02:35 AM   #4
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AF isn't perfect. As the K-x manual says:
QuoteQuote:
"Subjects that are difficult to focus on
The autofocus mechanism is not perfect. Focusing may be difficult
when taking pictures under the following conditions. These also apply
to manual focusing using the focus indicator ] in the viewfinder.
(a) Extremely low-contrast subjects such as a white wall in the
focusing area
(b) Subjects which do not reflect much light within the focusing
area
(c) Fast moving objects
(d) Strongly reflected light or strong backlighting (bright
background)
(e) If repeating vertical or horizontal line patterns appear within
the focusing area
(f) Multiple subjects in the foreground and background within the
focusing area
You may also get better, more reliable and quicker AF results by selecting a narrower AF focus area than the default.

I usually use the 'AF 5' or 'Spot' setting for AF, in order to make sure that the AF is locking onto subjects only within a narrow field of view around the centre of the frame. P-117 of the K-x manual describes how to set the AF focus area.

Also pls note that if you are using a filter on your lens (eg a UV or 'daylight' or 'protection' filter on your lens) they can often cause problems with AF because they are often of poor optical quality. If you are using such a filter, ditch it.

08-16-2010, 02:40 AM   #5
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While using the viewfinder if it can't find focus it should whip back and and forth through the focus range once, but really really fast, and then give up

While looking through the viewfinder, if it can find focus then it should be pretty rapid, the focus should jump right to the in focus point, maybe a tiny little bit of jitter after the initial jump but not much, and then beep when it's found focus

While using live view if it can't find focus is should crawl really slow throughout the entire range and then just stop after it's gone through once

While using live view if it can find focus it should craw really slowly throughout the entire focus range, and then after it's gone through completely, it will jump right back to the in focus point and beep to confirm, as well as a green box (or two or three) appearing on the screen

is this what's happening? because if so then that's totally normal
08-16-2010, 04:57 AM   #6
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I have a UV filter on so will try without

Thanks for the advise

Mark
08-16-2010, 04:58 AM   #7
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Thanks again - will try tonight and see how i get on

Mark
08-16-2010, 12:13 PM   #8
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"Tonight" = low light. In which case, slow focus is pretty normal.

08-16-2010, 06:19 PM   #9
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focus

seems to be an ongoing issue as in past DLR, would be nice if fixed, but solid colors , like a wall or sky, the camera will not take a picture in AF mode, no real fix, but I am going to try the option of focus with 1 segment in center to focus to take wedding pictures in about a week.
08-16-2010, 06:42 PM   #10
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make sure your subject is clearly defined, refer to page 65 of the manual.

did you change the focusing area? you might want to set it to center of the viewfinder (page 117)
08-17-2010, 01:30 AM   #11
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Changed to spot focusing on the modes that allow it - did seem to improve so many thanks for the advise - looking forward to the weekend when have some time in DAYLIGHT to experiment further
08-17-2010, 01:36 AM   #12
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QuoteOriginally posted by markjbamber Quote
I have a UV filter on so will try without

Thanks for the advise

Mark
The image below illustrates why some UV filters can cause problems with AF. As you can see, a poor UV filter (eg the Tiffen in this example) can make your lens 10% darker, and it can also make your image murkier and softer too.

AF works best when there is lots of light, and lots of contrast, in a scene. So understandably anything that makes your lens both darker AND softer will make your AF much less effective.


From the UV filter review at lenstip.com
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