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12-14-2007, 10:36 PM   #1
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Focusing speed & Pentax lenses

I have the FA43, FA77 & Sigma 18-50/2.8. The Sigma focuses noticeably faster than either of the FA lenses. I'm wondering whether the FA35 and FA50 focus faster than the FA43. What is your experience?

12-16-2007, 10:38 AM   #2
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Sorry to answer your question with one of my own, but do you like the Sigma 18-50, f2.8? Is it the newer "macro" version? I'm thinking of getting that one instead of the kit lens on the K10D since Tamron does not make their 17-50, f2.8 in Pentax mount. I'm happy to hear it has faster focus speed.
12-16-2007, 07:03 PM   #3
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I love this lens. It's very sharp, the color are fantastic, and the semi-macro capability is great. Sigma rates it as 1:3 but PopPhoto says it's closer to 1:2.5, and I agree. I think this is the best zoom in this range available for the K10D right now.
12-16-2007, 08:03 PM   #4
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The FA43 and 77 are some of the slower AF lenses by Pentax, the FA31 is abit faster in this category but not by much. The FA*85/1.4 and FA*28-70 are considerable faster than all the limiteds, the FA*200/2.8 and FA300/4.5 are quite faster too, and I'm talking about my own experience.

The AF w/ FA35/2 is abit faster than the FA50/1.4 IIRIC, which is also faster than the FA43/77. But they can't compete with the FA*85/1.4, and the FA*28-70 as far as AF speed is concerned


The Sigma zoom lenses (DC 18-50, DC 17-70 and etc) have relative shorter travel distance (from infinity to min focus distance), and they are very good in picking up contrast area even under low light, that's why they are faster in AF. AF w/ Sigma DC17-70 is as fast if not faster than the DA*16-50/2.8 even under low light condition.

12-16-2007, 08:24 PM   #5
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QuoteOriginally posted by frank Quote
The Sigma zoom lenses (DC 18-50, DC 17-70 and etc) ... are very good in picking up contrast area even under low light, that's why they are faster in AF.
Could someone please explain how/why the Sigma 17-70, being f/2.8-4.5, can pick up contrast better than the FA50/1.4 and the Limiteds?
I'd have thought it's a function of the camera enhanced by faster lenses.
Thanks.

PS: not discussing its shorter throw, just picking up contrast.

Last edited by Kguru; 12-16-2007 at 08:30 PM.
12-16-2007, 08:35 PM   #6
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QuoteOriginally posted by frank Quote
The FA43 and 77 are some of the slower AF lenses by Pentax, the FA31 is abit faster in this category but not by much. The FA*85/1.4 and FA*28-70 are considerable faster than all the limiteds, the FA*200/2.8 and FA300/4.5 are quite faster too, and I'm talking about my own experience.

The AF w/ FA35/2 is abit faster than the FA50/1.4 IIRIC, which is also faster than the FA43/77. But they can't compete with the FA*85/1.4, and the FA*28-70 as far as AF speed is concerned


The Sigma zoom lenses (DC 18-50, DC 17-70 and etc) have relative shorter travel distance (from infinity to min focus distance), and they are very good in picking up contrast area even under low light, that's why they are faster in AF. AF w/ Sigma DC17-70 is as fast if not faster than the DA*16-50/2.8 even under low light condition.

Thanks, this is very helpful. I think I may have to replace my FA43, as hard as it is to imagine. It just focuses too slowly for my needs. I guess the FA35 would be the best choice in terms of focusing speed in the same focal length range, with the FA50/1.4 not far behind. Since I shoot so much in low light, I might opt for the 50/1.4.

Then again, maybe I should hang on and see how the DA35 SDM is. But I have no idea when it's supposed to come out.

In the meantime, my Sigma 18-50 focuses pretty quickly on the K10D.
12-16-2007, 09:40 PM   #7
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QuoteOriginally posted by Kguru Quote
Could someone please explain how/why the Sigma 17-70, being f/2.8-4.5, can pick up contrast better than the FA50/1.4 and the Limiteds?
I'd have thought it's a function of the camera enhanced by faster lenses.
Thanks.

PS: not discussing its shorter throw, just picking up contrast.
I don't know why, but does notice that the Sigma 1770 focus pretty fast even under low light with less hunting. Sometimes I have AF problem with the DA14, DA*1650 and FA*2870 when the contrast is too low (for outdoor landscape in a cloudy weather and indoor low light), but seldom have this problem with the Sigma 1770. For the FA*2870 and DA14, sometimes I have to switch to MF ...
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