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07-18-2011, 11:57 PM   #1
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SMC P FA 100-300mm f4.7-5.8 AF speed on a K-7/K-5

I have been using this silver lens for few months now on my K-x. I love the lens for it's sharpness, colors and light weight. The only thing that bothers me is it's AF. What I observed is this - if the subject is away from the pre-focused distance then the lens AFs pretty fast.

If the subject is behind the pre-focused distance then it focuses all the way back to the min. focus distance and then focus back on the subject. This whole phenomenon takes place slowly, slower than Sigma 70-300mm DG Macro lens. So in many cases where the subject moves dynamically MF is the only choice left with this lens.

BTW I set 11 AF points but always place the subject at the centre of the frame because the centre AF sensor is faster. Are there any improvements suggested in this setup?

I am wondering if anybody used this lens on a K-5 and found any improvements in the AF speed.

Cheers
Guna

07-19-2011, 12:28 AM   #2
hcc
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Have you tried centre focus?

Many Pentaxians do recommend/prefer to use centre focus. With MF lenses, I feel that centre focus is a must to combine with Catch-in-Focus.

Hope that the comment may help.
07-19-2011, 01:41 AM   #3
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QuoteOriginally posted by hcc Quote
Have you tried centre focus?
I have to try this out. Is there a perceivable difference b/n having 11 point af but positioning the subject in the centre of the frame and explicitly choosing centre point of focus?

Guna
07-19-2011, 01:51 AM   #4
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QuoteOriginally posted by gut1kor Quote
Is there a perceivable difference b/n having 11 point af but positioning the subject in the centre of the frame and explicitly choosing centre point of focus?
With a single-point centre focus, the AF is less likely to get it wrong and some threads suggested that the AF would be faster. (I would not comment as I have always used centre focus right from the start, and I did the same before on my previous camera.)

07-19-2011, 06:23 AM   #5
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I agree with center focus, with a nuance : I manually select my focus point (and try to steer away from the two side points) but I don't always use center.

My FA 100-300 is not a speedster, but it focuses pretty decently on my K20D. It sometimes goes back to the min focus distance, as you describe, but that's usually when the subject is not very contrasty. For instance, on a face, focus on the eye instead of the cheek
07-19-2011, 07:59 AM   #6
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QuoteOriginally posted by bdery Quote
My FA 100-300 is not a speedster, but it focuses pretty decently on my K20D
Is it fast enough on your K20D to focus on bird in flight?
07-20-2011, 04:58 AM   #7
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QuoteOriginally posted by gut1kor Quote
Is it fast enough on your K20D to focus on bird in flight?
If prefocused in the general range of the bird, yes by all means. Otherwise, yes with good technique (keeping the bird on the AF spot, for instance).

It's a relatively inexpensive and slow lens (even if I find its results excellent by all accounts) so don't expect lightning-fast performances. The AF system has to work harder since less light is available.
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