K20d vs K7: AF with poor light

With my k20d I have problems when there is poor light, more photo of the face of my sons are out of focus. I know that there is a problem with focus in this condition with pentax camera, but the k7 really resolve this problem?

No equipment is perfect. You can usually find a way to get things to work with a little perseverance.

Any focus system will find it more difficult to operate in low light. Using a flashgun with a focus-assist beam will help; as will focussing manually; as will pointing the camera at a clear edge (the same distance away). Cameras need contrast in order to focus.

G

Possibly this is dependent on the lens in use.

When I use a 50mm f1.7 or 50mm f1.4 I have no problems focusing, even in situations where it's so dark that it woul be hard to focus manually. In these situations the K20D is better than eyesight.

However, with a zoom that may end up at f5.6 at the long end the ability to focus in low light will be reduced.

What lens are you using when you experience focusing problems?

With 18-250 pentax or 50 1,7 no problem, with 70-200 2,8 apo (not hsm not dg) there are problems with low light (but not always).

Is the low-light AF with the K20D better than the K10D?

And (anyone that's had both), how does the K-7's low light AF compare with the K20D's?

If there's one thing that would really push me to upgrade it would be if that was substantially better.

The K20D will autofocus down to EV -1 with the 50mm f1.4 lens. That's almost pitch black. I think the K10D is nominally the same.

But regardless of that the K20D is a leap forward in image quality, so I'd really urge you to upgrade at least to that. Substantially better? Yes.

The K7 Focus assist can be masked by a large diameter lens but if you have a flashgun with SB mode then that can perform the same function as the assist light, The flash does not have any effect on the exposure. It only performs to assist the Autofocus.
If you would like to focus manually then you could try one of the replacement sceens by Katzeyelink with a split circle in the centre.
Regards - Pete.