[pingu]

Have been using k-30 for 3 years with my lenses below and I am very pleased. For still photography I had great results.

For moving subjects - I used Continuous shooting(view finder) for great results too in the past, but issue for me is when shooting wildlife i.e. my 2 year old son with my wife . I use Expanded AF , center-weighted metering with view finder(Lens - Sigma 18-35 1.8). If I try to keep the square[red/pink dotted Expanded EAF] focus on my wife it keeps track of her , but my son who is running ahead of her is not in focus. I usually end up having only one of them in focus in all the continuous shots.

is my shooting technique at fault or do I need to upgrade for more AF points?


My lenses

Sigma 18-35mm 1.8 DC HSM Art - Go to lens
Pentax DA 50mm f1.8 [used it extensively before I bought Sigma]
Pentax 18-55mm kit lens [used initially]

[BigMackCam]

If you're focusing on your wife and she's in focus as you track, it's working just fine. It's quite normal that objects in front of or behind her will be out of focus (to a greater or lesser extent, depending on the aperture you're shooting at). Using a narrower aperture (for instance, f/5.6 instead of f/2.8) will increase the depth of field, and hence the range of acceptable sharpness in front of and behind the focus point. If your son is typically between you and your wife, I'd focus on him, as there will be more distance behind the focus point, rather than in front, that will be acceptably sharp. Does that make sense?

[swanlefitte]

That would be because you can only get an area in focus on a plane parallel to the sensor. The depth of this fields area of acceptable focus, or the depth of field, is only so deep. If they are not both inside this area you can't get them both in focus. The wider the focal length, the farther away you are, and the more you close the aperture can all increase your depth of field Dof. There are Dof calculators online and for download where you can see what will work.

[Adam]

In this case it sounds like there's an easy solution: stop down more. Since the 18-35mm is fairly wide, you should be able to get everyone in the frame and in focus at the same time

Adam
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[normhead]

Or in other words use a WA lens and ƒ8 and you should do just fine.

[pingu]

It makes sense. Narrow aperture would add more depth of field and hence subjects in front and back would be in focus. How did I forget this? . I usually shoot at ISO 100 with Aperture Priority and late evening to avoid harsh light. As it gets darker I step up to 1.8. I need to step down and guess need to increase ISO range a little ( I was worried about the noise).

[normhead]

It makes sense. Narrow aperture would add more depth of field and hence subjects in front and back would be in focus. How did I forget this? . I usually shoot at ISO 100 with Aperture Priority and late evening to avoid harsh light. As it gets darker I step up to 1.8.

e.g. Attached photo is shot at 8 PM with Aperture Priority - ISO 100(fixed), f/1.8 and 1/100 sec . I need to step down and guess need to increase ISO range a little ( I was worried about the noise).

You can safely go to 800 ISO without noise becoming an issue.

[swanlefitte]

Using f4 at 5', 20mm gives you over 3' dof at 35mm 5' gives you 1'dof. Stop down, step back, zoom out, and crop.