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04-08-2012, 08:56 PM   #1
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Screw Drive Bigma

I'm looking at a 50-500 Sigma EX, not the HSM model. How is the auto focus on a K-5 with this lens? Will it hunt from one end of the focus range to the other and drive me nuts?

04-08-2012, 10:00 PM   #2
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I have the EX version and K-5 and I haven't had any issues like that with AF. Although, if you are far from your subject or if your subject is very small, it is hard to get precise focus at 50mm so don't expect amazing results from a 50 f/4.

I have some quick sample images here, if you'd like to take a look (you can see what I mean by the 50mm thing) ---> Login to a private album
Password to album is "pentax".
04-08-2012, 10:15 PM   #3
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Thanks for the images.
04-08-2012, 11:58 PM   #4
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I have found it OK with my K5. In a dull flat scene it can struggle to start focusing. It's a versatile lens and rather remarkable, but don't expect it to perform the same level as a $15,000 kit of prime lenses. At 500mm and infinity my copy is soft so it wouldn't matter if the focus wasn't spot on. For a time 1o zoom the focus from one end to the other is short. I don't know how they did it.

I eventually replaced my bigma with a sigma 500 5.4 and the pentax 60-250. My bigma stood up to some very hard work.

Last edited by Bob from Aus; 04-09-2012 at 04:37 AM.
04-10-2012, 07:03 AM   #5
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I have the Sigma 50-500mm f4-6.3 EX DG and there's no problems with the focus. It's fast and accurate and as K-5 has exceptionally low noise I'll often use higher ISO with the 50-500.
04-10-2012, 08:33 AM   #6
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I had that lens and the Autofocus was fine. Remember to use multi point auto focus for BIF. Centerpoint AF on Birds in flight will do that some.

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