[biz-engineer]

Knowing my luck the kids will be smiling and looking at me outside the focus zone and looking elsewhere or blinking in the zone.

The problem is you have to understand that cameras will always have a limitation, and so it is not possible to photographs anything in any conditions. Basically, the photographer has to use the camera for what it's for. If I wanted to photograph a gun bullet in flight, even a Sony A9 wouldn't be fast enough, everything is relative, I could go complain to Sony that I need something faster. Also, I may want to not use a tripod in the dark because tripod is heavy to carry, I'd ask for a zoom lens with f0.25 aperture so that I can shoot in the dark hand held. But I don't think this way: the way I think is what my camera can do? and take photos based on what my camera can reasonably do.

[phoebus]

Have you tried AFS centre point only for this? With focus-priority release, this seems to me to the quickest and most precise focusing mode. No guarantees! Not got the 24-70, but the 28-105 is pretty quick at focusing. Maybe more success at the long end where not too much mechanical stuff is required to change focus.

This is pure conjecture, but I suspect that the more focus points in use, the longer it takes to get a 'decision' from the AF, and with no obvious motion trend taken on the Z axis motion, the further from focus measurement to shutter release. (For conjecture read 'guess' - nothing more or less) ;-)

[biz-engineer]

When I started wild life photography, I was walking without care and animals where flying away before I would be close enough to get any decent photo, then I thought "I need a 2000mm lens", but when I looked at the award winning bird photographer I found out he was using a 300mm lens, then I realized even if I bought the Canon 600 f4 for 12000 euros it wouldn't give me 2000mm, so I had no choice but to improve my technique, every time I improve my technique it costs me nothing, however every-time I buy gear to compensate for lack of technique it costs me money.

Now, with regards to photographing kids, would it be possible that you tell kids not to move in all directions when you try to photograph them, just tell them that you can't photographs them correctly if they are moving in unpredictable way, you could even photograph them with the Pentax camera and lens you already have without spending $1.

[clackers]

Hmmm again! I get it but I'm not sure this would work in my scenario. Knowing my luck the kids will be smiling and looking at me outside the focus zone and looking elsewhere or blinking in the zone. They aren't going to know where the zone is or even that it exists.

Look at what a sports photographer does … they choose the location with the best background and where the action's going to happen, and where the position means the faces are going to be up and into the light.

If there's a team of photographers, they can choose three or four locations and sit there for the whole event, if there's one they can take one quarter of the shots in one location, another quarter in a second, and so on, so that there's variety in the keepers.

It's a little like bird photography, you know in advance where the critters will come to you, and snap away. I quite like both shooting and taking part in running events.

[normhead]

When I started wild life photography, I was walking without care and animals where flying away before I would be close enough to get any decent photo, then I thought "I need a 2000mm lens", but when I looked at the award winning bird photographer I found out he was using a 300mm lens, then I realized even if I bought the Canon 600 f4 for 12000 euros it wouldn't give me 2000mm, so I had no choice but to improve my technique, every time I improve my technique it costs me nothing, however every-time I buy gear to compensate for lack of technique it costs me money.

Now, with regards to photographing kids, would it be possible that you tell kids not to move in all directions when you try to photograph them, just tell them that you can't photographs them correctly if they are moving in unpredictable way, you could even photograph them with the Pentax camera and lens you already have without spending $1.

Do the wedding photographer thing, hand up palm out to stop them, thumbs up when you have what you want, and step out of their way.

[Mundj]

I do not have a K1 and neither of these lenses. But I do own a K7, K3, a DA 16-50 f2.8 and a DA 18-135 f4.5-5.6. In looking at the reviews and specs I would offer the following. The 24-70 is twice the weight and twice the price of the 28-105. It is similar in size and build to the DA 16-50 I own and have been very disappointed with after spending almost $800 to buy and another $300 to repair. The 28-105 is similar in design to the 18-135 I own and also utilizes a DC motor that I find to be very fast and reliable. My suggestion would be to either buy the 28-105 and try it to see if it meets your requirements and if not return it or to rent both and see which meets your requirements.

Regardless, good shooting.