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Old Dec 28, 2008, 11:02 AM   #1
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Morning Everyone,

At times I seem to have problems with the shutter on my K100D (at times). There appears to be no problem, other than it just does not want to take the image when pressed, in certain situations (only occours when in autofocus mode).

Scenario - My wife and I were up on Mummy Mountain, taking a walk along with some pictures. I was trying to take an image of a cactus up on the hillside. The camera was in autofocus and was focused in the viewfinder. I depressed the shutter all the way, and in the viewfinder the "focus indicator" (on the bottom bar, i.e., the "viewfinder indicators") was blinking, and the camera was not taking the image. This has happened in the past and at times it just takes a longer period of time for the shutter to release, but it usually goes ahead and takes the image (10, 20, 30 seconds). This time, it just sat there blinking, so I switched the autofocus to manual, and it immediately took the image. I have searched the manual and have come up with nothing.

The scene had high contrast between the area in shadow and the lit area.

... Here is a bit more information.

Capture mode - Auto Picture (Landscape)
Metering mode - Multi-segment metering
Autofocus mode - Autofocus (note to get the shutter to actually release I switched to Manual)
Autofocus area - Automatic
Firmware - K100D version 1.0

Here is the image in question.....
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Old Dec 28, 2008, 12:48 PM   #2
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When set to AF mode, the camera only takes the picture (releases the shutter) when it judges the picture focused. This is shown by a permanently lit symbol (the green hexagon). When the hexagon is blinking, it indicates that the picture is near but not yet at focus, thus the camera won't release the shutter.

To me it happens mainly in low light. I find this feature pretty annoying, and I often shift to manual focus mode to avoid it. It happens both with my DS and with my K20D, so I don't think there's anything malfunctioning with your camera. Some of our members use the feature to get a "focus trap", please someone who use that explain.

Kjell
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Old Dec 28, 2008, 2:19 PM   #3
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Thanks Kjell!

Its been occurring more frequently lately, however I have been using my (recently acquired) 12-24 lens with a polarizing filter much more frequently, of late. Also, with the sun angles, I have been getting much more shade and shadows (as opposed to summer here) and that's where, I am starting to see the problem occur more often than not. I am starting to believe that with images that take in shadows, when using a filter, the auto-focusing algorithm is just unable to cope. Apparently, with at least one autofocus point in a shadow area, autofocusing just toggles in and out...

I just wish that the manual was more clear in terms of what the flashing hexagon (focus indicator) implied.

Thanks again...


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Old Dec 28, 2008, 5:32 PM   #4
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I've found that the 12-24 doesn't get focus as easily as some of my other lenses do - don't know if that has to do with the fact it's wide angle and that the vertical or horizontal lines are usually smaller or not. I don't worry too much about it since the DOF is so big that being off a bit won't make that much difference. Adding a polarizer does affect the focusing, even a circular polarizer. I figured it has to do with the fact it cuts down on the amount of light entering the AF mechanism.

I'm not crazy about a circular polarizer on the 12-24 if there's lots of sky - the color is often not consistent across it. Are you getting good results with it in these circumstances, or are you using the polarizer to deal with reflected light from water, etc. with little sky involved?
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Old Dec 28, 2008, 7:08 PM   #5
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Hey IO.,
I'm not familiar with the K100, but I've had the same problem with both the GX10 and the new K20d.you might try the spot focusing mode and see if that helps.
:-?
GW :bye:
also, I have found the owners manual almost useless, I got one of the Magic lantern books for the K10 and learned a lot! well worth the price!
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Old Dec 28, 2008, 9:16 PM   #6
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Hi IO,

This might sound like a little wierd, but I read in another forum that some users find that instead of using center point focusing mode, their Pentax DSLRs focus more accurately and quickly when in selective focus mode, with the center focus point selected.

They've also found that some of the focus points are more accurate than others, but there seemed to be no consistancy to which ones.

If you've got a lens or lens/filter combo that has problems focusing, this might be something to try.

Scott
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Old Dec 29, 2008, 1:33 AM   #7
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Is there anything published to say which focus points are cross-type and which only focus on one plane? That would definitely make a difference and if someone was using a non-cross-type then it would make sense that it would be inconsistent. What is interesting is that some would find selecting the center focus point from the selectable menu being more accurate than using the center focus position.

I have noticed that sometimes moving the camera slightly will help the 12-24 get a focus lock when it's struggling. I've always put this down to the fact that as a wide angle, often the lines are smaller and the camera doesn't "see" them as well. Or that the focus spot isn't quite where the dot is (also possible) and moving the camera a bit gets the line to cross the sensor.
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Old Dec 29, 2008, 9:10 AM   #8
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bilybianca wrote:
Quote:
Some of our members use the feature to get a "focus trap", please someone who use that explain.

Kjell

IO ... I can't say I've noticed your problem with my K100D, then again I don't have a wide angle zoom lens in anywhere near the range you mention.

No one seems to have jumped in on "Focus Trap"... I use the technique fairly often, it's very useful in macro work, hope I'm not teaching anyone tos**k eggs. ...

As Kjell has already said when the body is set to AF the shutter won't trigger until focus is achieved, it does need fairly good light and contrast for it to work, with FT

using MF lenses, and camera set to AF ... the method is to either compose your shot, and then adjust focus until the shutter operates, or my technique is to set the

requiredfocus distance, and move the camera in or out until the trigger point is reached. If either the onboard flash or an external one is in use they will fire

simultaneously. FT is possible with M42 lens also, but I had no real success until I adopted Gumnuts foil washer method of shorting the body contacts as outlined in

this thread. ...

http://forums.steves-digicams.com/fo...818255#p818255

I think I've read someplace that this fools the camera, and it acts as if an "A" lens is mounted. I hope that's right. ... Jack

Edit. ... I missed a vital point ... you must take full pressure on the shutter release when focussing, camera then operates when correct focus is reached. Sorry about that ... Jack.
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Old Dec 29, 2008, 11:28 AM   #9
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Good Morning Everyone,

Thanks for all the replies and the thoughts! They are all very helpful. The more I consider the problem, and going back to see what I have shot, I am coming to the conclusion that the problem (if you could call it a problem) is based on the design of the auto-focusing algorithm. Here is my reasoning...

Of late I have been shooting with somewhat radical sun angles and heavy shadows - early morning sunrises and late afternoon, evening sunsets - and to add to the situation at the winter solstis - where the sun angles (here in AZ) are at their extremes. The example I showed has 3 distinct regions, blue sky, sun lite hillside and hillside in shadow. Now when I pointed the camera directly into the shade, it immediately locked and took the image.

The autofocusing works great with a filter in "normal" environments, however with filter and some type of extreme differences within the frame (I am finding), the auto-focusing tends to have a bit of a problem. If there is a clear difference (as in two regions), sky and shade - usually no problems (locks immediately), however with 3 or more regions - such as the example, I seem to be having more problems, amplified with the polarizing filter. Remove the filter in the extreme situations, and it locks on much easier. I am starting to think that this is an extreme example of hunting - in this case too many areas to try to handle. [I am thinking that since is does well with a single boundry, it is getting confused - as in focuses across one boundry, and then brings in the third region. So it does well focusing on region 1 and 2, and then tries to focus across region 2 and 3. Since I am on a hillside, quickly rising away from me, I am getting the extreme toggling between the two radically different regions - both in lighting and distance.]

So the polarizer tends to magnify the problems, in the extreme situations. I have been using the filter to pull out the definition from the clouds that have been coming through lately. So that is another point that I have stumbled upon. I know that I have been pushing the extremes of the envelope here - the wide angle lens, with the filter. On this topic, I went with a Nikon polarizing ultra thin filter (and paid a bit more), because I wanted to reduce the potential of viginetting. The real thin polarizing filter reduces the viginiting due to the wide angle of the lens - and so far, there has not been a problem at all.

The suggestions to use the other focusing modes, I have not done a lot with, and need to try them out.

Here is an example of not the problem, but of the extremes I have been shooting. Its about a hour before sunset. The face of Camelback Mountain is in deep shadows, becaure at this time of the year, the sun rises, tracks and sets behind the mountain. The lens is wide, and I am essentially shooting into the sun (actually the 12-24 does well - better than most, in this situation), and I have the polarizing filter on, hence the viginetting on the left hand side forced by the sun on the extreme right side.
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Old Dec 29, 2008, 12:11 PM   #10
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snostorm wrote:
Quote:
This might sound like a little wierd, but I read in another forum that some users find that instead of using center point focusing mode, their Pentax DSLRs focus more accurately and quickly when in selective focus mode, with the center focus point selected.

They've also found that some of the focus points are more accurate than others, but there seemed to be no consistancy to which ones.
Really interesting, Scott. I tend to compose a lot with an off-center focal point, so I have just gotten used to using the selective focus for much of my shooting. I had never thought about selective focus being faster in the center position, but now that you mention it, I think that is the case. I had attributed the better focus performance on doing a better job of selecting the point at which to focus, but you may be on to something. Definitely an interesting hypothesis on which to experiment.

Paul
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