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08-03-2009, 09:28 AM   #1
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K7 AF-C Burst Mode Question

I have a question about the K7 when using burst mode with AF-C.

My K-10 and K-20 both sometimes hesitate shooting in this set-up. Not every time and not consistently. Sometimes at the start of the burst and sometimes during the burst.

DPReview alluded to this in their K10 review when testing burst mode.

This has a tendency to cost me shots I should be getting and I'm not really sure what causes it. If it is a hesitation because of focus AF-C should alleviate that.

Does the K7 do this also? I haven't been able to try one in hand yet. I am going to attend the Orlando Road Trip event but that is still a couple of weeks away.

Thanks for your replies in advance.
Dennis

08-03-2009, 10:37 AM   #2
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Yes, the k-7 hesitates in AF-C in burst mode. From what I can tell, even though you don't have to be in focus for the shutter to release, the camera will do it's best to achieve focus before releasing the shutter.

From the playing that I've done with the k-7 and both the 50-135 and the FA*400 it will shoot so long as it's got a good line on the subject (in my case, my daughters running towards me). The farther they are away, the easier it is for the focus to keep up and therefore, a higher frame rate. As they get closer and the focus has to move more to keep up/catch up with the subject, the frame rate drops.

The highest frame rate I was able to achieve (looking at the time-stamps in the exif data) was 4 frames within 1 second (ie, 4 timestamps all identical). The slowest was about 1 frame every second or two as they got within 15 or so feet (w/ firmware 1.01).

As for the results compared to my old k10, there is no comparison. The k10's AF-C was hit and (mostly) miss whereas I had most photos within acceptable focus from beginning to near the end with the k-7 - usually the last shot tanking completely or (because I was down low to the ground) a sharp nostril shot (which I will use when my kids are old enough as leverage for a tidy retirement home )

The above was with the FA*400. The 50-135 is a much slower focusing lens and therefore there's more delay as it plods along to get focus. So the lens will make a difference in what you can achieve and how much time it takes to achieve it (to my limited experience anyways).

Hope this helps,
08-03-2009, 11:27 AM   #3
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Thanks for the quick reply, Andrew.
The hesitation is becomming a real issue for me.
What I am doing is shooting swim meets and trying to get the swimmers coming off the blocks. With the hesitation I am often missing the best moments of the sequence, sometimes going from the initial movement of the swimmer to the splash afterwards and nothing in between, or the body half in the water.
I am using a Sigma EX 100-300 F4, which is a very fast focusing lens.
Dennis
08-03-2009, 11:51 AM   #4
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I was shooting some swim meets with my istDs2 and would switch to manual focus after the camera had achieved focus using af. Burst works much better that way. If your depth-of-field is sufficient, you shouldn't have a focus problem, depending on your angle-of-attack.

08-03-2009, 12:21 PM   #5
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Thanks for that Walter.
It is always a battle early and late in the day to keep the shutter speed up so I run the lens pretty open, thus limiting the DOF. When the sun gets up sufficiently it should be easier to do because I can stop down and still keep the shutter speed up.
One thing I definitely like is TAV mode. Set the shutter speed and aperture and let the camera adjust ISO to maintain the shooting parameters you set. Very cool thinking there.
Dennis
08-03-2009, 12:31 PM   #6
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No problem, Dennis.

I don't know how the k20 stacks up or the 100-300 for that matter, but the screw-driven AF lenses got a real boost with the in-body focus motor on the k-7 over the k10. I think you'll find much less hesitation with the k-7, but I've never tried catching a shallow-dive off the blocks before (with any body) so what I think may not count for much

I'm going to have to employ the kids for a couple of new 'tests' now
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