[kcupp95]

I have a 1 year old K5-ii.

I was using it with my 50mm f1.8 lens to do some portraits. Quite basic - 2 people standing together in front of a cream coloured wall in good natural lighting.

I had aperture set to 1.8 and was standing at a reasonable distance away - far enough away to get 2 people in a 50mm shot.

The autofocus absolutely struggled with the photos. I could hear it focusing quite loudly and it would often "whir in and out" and be completely unfocused and would take quite a few goes of changing between auto focus and select point focus and half-pressing the shutter button, which was really a pain in the bum.

The cause of the problem is
a) user error - please hit me up with tips to avoid this
b) camera problem
c) lens problem

If it helps I've also recently had problems with my 18-135mm not autofocusing at certain focal lengths in daylight landscapes regardless of aperture.......

[phoenixvision]

First check the lens...maybe this is obvious, but if the lens isnt clean, this will definitely effect the af....it doesnt sound like low light or direct sunlight were a problem....were you focusing on something totally black possibly? Otherwise if the lens is clean and the light is bright and normal, it could be a camera issue, but if this is only happening selectively...doesnt sound like it.....clean the lens and shoot around with it in normal conditions and see if you have a prroblem....if you do, change the lens clean it and try with a new lens, if it works fine, its a lens issue, if neither works, its a camera issue.....of course make sure the af switch on the side of the camera is completely on af and not slightly off, this can sometime get it to keep refocusing every time you move slightly......hope this helps...

[esrandall]

Maybe a metering issue, or something with the screw drive. Shaky hands with it set on AF-C (I've had that happen while trying to shoot in breezy conditions, and the camera struggles to lock on). I would ask if you've tried remounting the lens, but if it's struggling with two lenses, sounds like a less isolated issue.

[stevebrot]

I had aperture set to 1.8 and was standing at a reasonable distance away - far enough away to get 2 people in a 50mm shot.

The autofocus absolutely struggled with the photos. I could hear it focusing quite loudly and it would often "whir in and out" and be completely unfocused and would take quite a few goes of changing between auto focus and select point focus and half-pressing the shutter button

• Your aperture setting does not affect the AF, neither does ISO or metering.
• The amount of light and subject contrast will affect the AF performance

The AF system needs something to focus on. A good example would be attempts to focus on a blank wall. In bright light the camera may succeed. In dim light, maybe not. It also does better with an unambiguous target.

Not being there to see exactly what is happening, it is hard to say what the problem is and whether there is a solution. I can offer a few tips:

• Make it easy for the camera to determine the intended focus point.* Switch to single point, center (aka "spot") if the system is hunting.
• Use AF-S unless you are tracking motion
• The AF system does better in good light and less well when the light is dim
• Remember that the camera does not "know" your intended point of focus

I own the DA 50/1.8 and have found the AF performance on my K-3 to be better than average. If you continue to have trouble with this particular lens and the AF works well with other lenses there is the outside chance that the focus mechanism is damaged or otherwise faulty. If you are having problems with all lenses in good light, with an unambiguous target, there may be a problem with the camera.


Steve

* When the focus point is set to auto, the system will make its best guess as to what should be in focus. Often enough this is the first point that has enough contrast to acquire focus. When that is ambiguous there may be some lag in the system as attempts are made on multiple points.

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Last edited by stevebrot; 11-05-2014 at 09:06 AM.

[esrandall]

• Your aperture setting does not affect the AF, neither does ISO or metering.
  [*]The amount of light and subject contrast will affect the AF performance

The AF system needs something to focus on. A good example would be attempts to focus on a blank wall. In bright light the camera may succeed. In dim light, maybe not. It also does better with an unambiguous target.

Not being there to see exactly what is happening, it is hard to say what the problem is and whether there is a solution. I can offer a few tips:

• Make it easy for the camera to determine the intended focus point.* Switch to single point, center (aka "spot") if the system is hunting.
• Use AF-S unless you are tracking motion
• The AF system does better in good light and less well when the light is dim
• Remember that the camera does not "know" your intended point of focus

I own the DA 50/1.8 and have found the AF performance on my K-3 to be better than average. If you continue to have trouble with this particular lens and the AF works well with other lenses there is the outside chance that the focus mechanism is damaged or otherwise faulty. If you are having problems with all lenses in good light, with an unambiguous target, there may be a problem with the camera.


Steve

* When the focus point is set to auto, the system will make its best guess as to what should be in focus. Often enough this is the first point that has enough contrast to acquire focus. When that is ambiguous there may be some lag in the system as attempts are made on multiple points.

My bad on the post I made. I'm getting the two things mixed up. Was treating it like it was struggling to have something to focus on, like the camera wasn't getting enough light to lock on to anything, and was treating the two areas as being the same thing. I just read another thread mentioning that people sometimes treat them as the same thing, when they aren't. Add me to that list of people that have a lot to learn.

Thanks for the always useful information

[lister6520]

I once had very similar symptoms with a K-r. In the end it turned out to be dirt, lots of it, on the AF optics at the bottom of the mirror box. Two of the focus points still worked properly (if manually selected) but the rest were all very erratic, including unfortunately the centre one.

I think the same can be caused by dirt on the mirror itself - it is actually partially transparent and light goes through it down to the focusing optics so any dirt or scratches on it can cause problems.

[phoenixvision]

Dp let us know how this all turns out...I am really curous after hearing all the possibilities, what you found.....

[snostorm]

it turned out to be dirt, lots of it, on the AF optics at the bottom of the mirror box.

This would be my first guess for a camera that suddenly started having focus problems with more than one lens. Any dust shaken off the sensor has to go somewhere, and I don't really trust the dust catcher strip under the sensor. I occasionally use the sensor cleaning mode and blow out the camera, even if there are no apparent dust particles on my sensor -- can't hurt. . .

Scott

[kcupp95]

Thanks everyone for the replies!! I have cleaned the lens and contact points on the mount for the lens and camera.

Not too sure how to check the mirror box for dirt - it definitely wouldn't surprise me if there was dirt in there!!!

Will see how I go over the next couple weeks - close friends just had a new baby and I'll be taking family photos whenever I'm visiting, so should have some good opportunities to test it out.