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07-31-2015, 04:58 AM   #136
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QuoteOriginally posted by Digitalis Quote
...but if it cannot AF accurately and reliably it is just a colossal waste of money and bag space.
Which must be why you keep using your own "colossal waste of money and bag space“ called Sigma 18-35/1.8.

Did some copies of that lens have AF issues on Pentax DSLRS?
Yes.

Are there many happy users without AF problems?
Yes.

Has anyone with problems ever properly followed up with Sigma Japan to see what the root cause is?
No, not to my knowledge.

I don't want to diminish the problems some people have and it would certainly be better if this were a non-topic but it is far from clear where to point the finger or even make forecasts about different products from the same manufacturer.


Last edited by Class A; 08-01-2015 at 01:44 AM.
07-31-2015, 05:17 AM   #137
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QuoteOriginally posted by Na Horuk Quote
And a bright aperture, good resolution, should allow AF even in fairly low light on different kinds of subjects.
It really has been a puzzle for me. The 35mm f1.4 AF works, but not consistently. Shoot the same Lens Align target 10 times with the same settings, distance and light, but the AF won't nail it 10 times. My three older K-mount Sigma's just work 10/10, even my NEX Sigma's.
07-31-2015, 11:47 PM   #138
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QuoteOriginally posted by rawr Quote
It really has been a puzzle for me. The 35mm f1.4 AF works, but not consistently. Shoot the same Lens Align target 10 times with the same settings, distance and light, but the AF won't nail it 10 times. My three older K-mount Sigma's just work 10/10, even my NEX Sigma's.
But are the others shoots at f/1.4? because for me FA50 does the same kind of crap.
08-01-2015, 01:02 AM   #139
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QuoteOriginally posted by Nicolas06 Quote
But are the others shoots at f/1.4? because for me FA50 does the same kind of crap.
My FA 50 is well-behaved, and does it's job OK. The only other f1.4 I have in K-mount is the SamYang 85mm, so I get no AF hassles with that.

But you may be correct. The combination of high resolving fast glass and high-sensitivity AF like the K-3's invites the sort of AF indecision I have been experiencing. As if every extra particle of dust or slight change in surface contrast in a scene invites another AF acquisition loop.

08-01-2015, 01:06 AM   #140
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QuoteOriginally posted by rawr Quote
My FA 50 is well-behaved, and does it's job OK. The only other f1.4 I have in K-mount is the SamYang 85mm, so I get no AF hassles with that.

But you may be correct. The combination of high resolving fast glass and high-sensitivity AF like the K-3's invites the sort of AF indecision I have been experiencing. As if every extra particle of dust or slight change in surface contrast in a scene invites another AF acquisition loop.
FA50 work much better with K3.
08-01-2015, 10:55 AM   #141
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QuoteOriginally posted by Na Horuk Quote
but why is the AF so weird with recent high-en Sigma lenses? You think its the camera manufacturers sabotaging Sigma, so they can't be too good? Or is the lens somehow odd? Because you'd think AF is a straightforward thing, check red and blue phase, adjust until it fits. And a bright aperture, good resolution, should allow AF even in fairly low light on different kinds of subjects.
I don't know about Pentax, but in the Nikon camp this is absolutely a possibility. Nikon does not like Sigma. They even sued Sigma over patent infringement regarding either their HSM autofocus, (versus Nikon's SWM) or their OS stabilization. (Versus Nikon's VR)

I forget who won the lawsuit, but I think it was a few million awarded to Nikon, I'm not sure. It has also been strongly rumored that Nikon tweaks their electronic communications from body-to-lens to cripple Sigma lenses from time to time on newer Nikon bodies. If you google "Sigma update lens firmware for Nikon issue" you'll come up with tons of official press releases. :-(

It's a shame they can't play nicer, but then again, all's fair in business and war. At least I think that's how the saying goes.

Sigma's solution of creating the AF calibration docking station is brilliant, and provides far more accurate and extensive calibration potential than even a Nikon or Canon setup. However, it can only correct for front/back focus, not completely erratic focus and un-reliable performance in certain light. Which is a problem I have indeed had lately with some of the Art lenses.

It's a shame, really, because I've owned two older EX lenses that performed flawlessly for me, the 50-150 2.8 and the 150 2.8 macro. I wish Pentax made a 150 or 180 2.8 macro that rivaled their 100 WR, but alas... Then again, I'm not really that much into macro as much as I was back then, and the Pentax 200 2.8 is actually shockingly lighter than even the Sigma 180 2.8, even if it did come in a Pentax mount. So, win-win there. I could probably cover the mid-range walk-around with the lightweight 55-300. I wish the 50-200 WR was as sharp as the 55-300, but it doesn't appear that way from the reviews here...

TLDR; aside from say maybe the 18-35 1.8 on a K-3 II, I'm losing reasons to concern myself with Sigma lenses. Unless they come out with a full-frame or APS-C ultra-wide that is faster than 2.8, that is... A 18-35 1.8 on a K-3 II and a ~16-24 f/2 on a full-frame Pentax would be truly unbeatable, for me as an astro-landscape photographer. :-D
08-03-2015, 06:16 AM   #142
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The thing I notice about this lens is its size. I compare all lenses to two yardsticks - my DA 50mm f/1.8 and my DA 18-250mm f/3.5-6.3. Having just carried the latter on a family vacation, I must declare that (a) I have no desire to carry anything bigger or heavier when travelling and (b) anything even remotely near its size has to match it for versatility, either in zoom range or in aperture or both. This is not that lens.
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