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03-06-2015, 08:23 AM   #1
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Sigma 18-35mm vs Pentax 20-40

Hey all,
I'm considering picking up a Sigma 18-35mm f/1.8 Art. It's a darn fine lens. I'm just worried about the AF performance really killing it for me. So, the other option would be the newly discounted 20-40. It's not as fast, and isn't as sharp or as wide but it's sealed, small, and it's guaranteed to focus more reliably.

Thoughts? My local camera shop actually has a K-mount 18-35mm and I've played with it. I could always just buy it, shoot with it, and return it if it's not up to scratch. I like Sigma and I like that their lenses are still all made in Japan. It's a company with integrity and I'd like to trust that they'll solve the AF issues eventually with an update.

03-06-2015, 08:35 AM - 1 Like   #2
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Sigma's AF performance in my view is more a design and/or software/firmware issue. It's not just a Pentax problem, Nikon and Canon has similar issues with the 18-35mm. I have one and I like it a lot, I got the dock and have it somewhat calibrated. If you don't want to go through all that then get the DA 20-40, a little slower but excellent in every regard.
03-06-2015, 09:22 AM - 1 Like   #3
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I also have the Sigma 18-35 and I'm satisfied with it. Yes sometimes the focus doesn't hit what I want, but my good/bad picture ratio is not so bad. For pictures taken indoor the sigma is a very good decision. For outdoor shots I'm unsure, I mean I didn't use too much the Sigma outdoor but I felt the AF makes more mistake outdoor. I had FA* 24 before the Sigma, but I ended up with selling the FA*. Maybe it is another lens for you to consider. I don't think that the 20-40 worths its price.

03-06-2015, 09:25 AM - 1 Like   #4
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I've used the 18-35 a lot, and it's been one of the best lenses I've ever used. That said, dont expect to be taking snapshots with it because you wont get them because the AF can be unreliable wide open. You need to take care setting up your shot, but once you do, the results are fantastic.

03-06-2015, 10:14 AM   #5
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Duplicate thread... please see
03-06-2015, 10:18 AM   #6
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Original Poster
Sorry for the duplicate. The site search didn't pick it up for whatever reason.

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