Sigma 18-35 f/1.8 Art Focus Issues Thread

Zafar Iqbal · 07-06-2015, 03:14 PM

Originally posted by rawr

You have to be very aware of the AF mode settings

I pondered about this and did some quick and dirty shots while on my way home from work.

My initial impression: 9 point expanded AF area gave better focus.

If AF-S focusing was off, then expanded AF would do the trick, or in general land the focus closer to the subject I was going for.

If AF-S focusing was spot on, then expanded AF would generally be a bit off and only occasionally (only ones, actually - amongst the 70ish shots I did) wander way off.

I've uploaded some of the most meaningful photos - You can see in captions, which photo used which AF mode.

Click t enter album:

Some of the last photos are shot using AF-S but nailed the focus on what should have been tricky?

I must admit I can't really make sense of this - also, if expanded AF area indeed improves focusing and AF-S is *that* bad then why have AF-S? Aaan, just to repeat myself, I haven't noticed the focusing being so tricky with my other cameras though they are not same model.

All photos were shot using Pentax 70mm Limited.

I'm open to whatever theories you guys may have - I just want to understand what's going on so I can move on from there.

Ps. photos can be viewed or downloaded in full resolution for pixel peeping.

Pps. I always used center point and never recomposed.

Zafar Iqbal · 07-24-2015, 10:47 AM

Some shots from few days ago: K-3 II and Sigma 18-35 f1.8:
https://zafariqbal.smugmug.com/Shares/2015/20150724a-PF/n-hVWPJq/

And some shots from today: K-3 II and Sigma 17-50 f2.8:
https://zafariqbal.smugmug.com/Shares/2015/20150724b-PF/n-qsJ2vD/

Center point used and no re-compositioning on any of the photos. Click on a photo to enlarge but itøs best to see full res photos to really see whats going on.

What do you guys think regarding focusing accuracy?

nicoprod · 08-03-2015, 07:55 PM - **2 Likes**

I got a used but mint copy of the 18-35 a few days ago, tested it in natural light the first day mostly at close range and was fairly satisfied with the AF. I took the risk of taking it to a wedding the following day and I was so weirded out by the AF behavior during the reception under electric light that I ended up calling the 17-50 to the rescue. The Sigma 17-50 is a decisive focuser, never readjust more than once if it ever does while the 18-35 micro adjusted often 2,3, 4 times before at times completely missing the target. I'm very much used to covering receptions in low light and the 17-50, or even better the 31 are much much more decisive than the copy of the 18-35 I got. I had another wedding the following day and left it home in favor of the 31....
I wanted to 18-35 so I can have it glued on one body and have a portrait lens on this other ( I always professionally shoot with 2 cameras). With that I was hoping to do all my indoor coverage without having to switch lens. It's not gonna happen for now. The 18-35 delivers amazing IQ but I can't afford missing money shots because of an unpredictable auto-focus. It's back in the box and being returned tomorrow.

**Digitalis** · 08-03-2015, 11:24 PM

Originally posted by Zafar Iqbal

What do you guys think regarding focusing accuracy?

Mine is still very hit-and-miss, regardless of light levels, AF mode or AF point used.

howieb101 · 08-04-2015, 12:41 AM - **1 Like**

Sad. A good item on paper. In reality less so. Good that Sigma continues to innovate though.

I wish Sigma could manage to make their lenses smaller though. I would like to get the Sigma 85mm F1.4 but I keep thinking I could get the relatively feather weight FA 77 F1.8. Low weight versus silent focus and faster aperture has stopped me buying either so far. No clear winner.

Howie Be

Zafar Iqbal · 08-04-2015, 12:42 AM

Thanks for the replies - I have 4 weddings this week (yes) and plan on following up with my findings about the lens and camerabodies shortly after this.

Class A · 08-04-2015, 02:34 AM

Originally posted by howieb101

A good item on paper. In reality less so.

Depends on whom you ask.

Some people are very happy and they naturally won't come this thread to make contributions.
The The Sigma 18-35 f/1.8 Art club continues to receive great submissions as well.

Originally posted by howieb101

I wish Sigma could manage to make their lenses smaller though.

I don't think Sigma leaves out opportunities to make their lenses smaller or lighter. I believe for the desired performance they have to be this size.

The FA 77/1.8 is a marvel in terms of its size and rendering but I'm not sure how many optical compromises were made to achieve this size. I guess it could have less vignetting, if it were bigger and a more complex construction could probably address the rather heavy purple fringing. Not sure either how the corners will look like on a high-MP count FF camera. I don't think this particular design could be launched as a modern lens today anymore. Which is something I regret, because I like the FA 77/1.8 like the other FA Ltd designs and I think if Pentax will update them, we won't see the same rendering anymore because certain flaws won't be excusable anymore.

**UncleVanya** · 08-04-2015, 10:45 AM

Originally posted by Class A

Depends on whom you ask.

Some people are very happy and they naturally won't come this thread to make contributions.
The The Sigma 18-35 f/1.8 Art club continues to receive great submissions as well.

People may still have significant focus failures and still make great images. The real question is keeper ratio...

nicoprod · 08-04-2015, 11:55 AM

Originally posted by UncleVanya

People may still have significant focus failures and still make great images. The real question is keeper ratio...

Yep, and for people who cover events, AF speed and accuracy is essential.

**UncleVanya** · 08-04-2015, 12:05 PM

Originally posted by nicoprod

Yep, and for people who cover events, AF speed and accuracy is essential.

I agree. I was trying to point out that the prevalence of great images from the lens has little to do with any AF problems it might have. People may not comment because there is little they can do to help the issue or they may not have the issue - lack of a post doesn't tell us which.

nicoprod · 08-04-2015, 01:37 PM

Originally posted by UncleVanya

I agree. I was trying to point out that the prevalence of great images from the lens has little to do with any AF problems it might have. People may not comment because there is little they can do to help the issue or they may not have the issue - lack of a post doesn't tell us which.

Yes it delivers very sharp and clear photos. It's definitely sharper than the FA 31 wide open. The 31 doesn't miss though and just renders better.

Class A · 08-04-2015, 02:28 PM

Originally posted by UncleVanya

People may not comment because there is little they can do to help the issue or they may not have the issue - lack of a post doesn't tell us which.

I have seen posters explicitly state that they don't have any AF problems. Another such explicit statement has been made in this thread. Yet, another follows the post I've just linked to, and I'm sure I could find many more such positive reports.

These statements do not fit into the theory of some, so they still speak as if their personal experiences could be generalised to everyone.

**UncleVanya** · 08-04-2015, 02:35 PM

Originally posted by Class A

I have seen posters explicitly state that they don't have any AF problems.

That doesn't fit into the theory of some, so they still speak as if their personal experiences could be generalised to everyone.

I have too - but the point made about the thread existing and many good pictures in it didn't address that. I'm stumped as to the delta between user opinions - I don't have this lens. I wanted it - I wanted it BAD... but the reports of the problems have scared me away.

Class A · 08-04-2015, 02:45 PM

Originally posted by UncleVanya

I have too - but the point made about the thread existing and many good pictures in it didn't address that.

Of course, keeper rate is important. But if everyone posting images made with the lens had to go through great pains to get them, we'd hear more about it, wouldn't we?

If you want the lens, if I were you, I'd buy the lens from a place with a good return policy or the dedication to satisfy you as a customer.

**UncleVanya** · 08-04-2015, 02:49 PM

Originally posted by Class A

Of course, keeper rate is important. But if everyone posting images made with the lens had to go through great pains to get them, we'd hear more about it, wouldn't we?

No that assumes everyone even posts. There are more people using the lens on Pentax than participate here or on any forum I suspect. Many suffering in silence or many happy as clams - no real way to know for sure. However the people asked about it seem to fall into one or the other camp and every review seems to have problems - that is informative.

As for a return policy. No that's not going to happen for now. I am staying away. If a great review comes out showing that the problems have been resolved I will be interested. Until then - no thank you. I have many outlets for my cash...

07-24-2015, 10:47 AM	#122
Zafar Iqbal Veteran Member Join Date: Oct 2010 Photos: Gallery Posts: 1,187	Some shots from few days ago: K-3 II and Sigma 18-35 f1.8: https://zafariqbal.smugmug.com/Shares/2015/20150724a-PF/n-hVWPJq/ And some shots from today: K-3 II and Sigma 17-50 f2.8: https://zafariqbal.smugmug.com/Shares/2015/20150724b-PF/n-qsJ2vD/ Center point used and no re-compositioning on any of the photos. Click on a photo to enlarge but itøs best to see full res photos to really see whats going on. What do you guys think regarding focusing accuracy? Last edited by Zafar Iqbal; 07-24-2015 at 10:54 AM.

08-04-2015, 02:28 PM	#132
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 10,928	Originally posted by UncleVanya People may not comment because there is little they can do to help the issue or they may not have the issue - lack of a post doesn't tell us which. I have seen posters explicitly state that they don't have any AF problems. Another such explicit statement has been made in this thread. Yet, another follows the post I've just linked to, and I'm sure I could find many more such positive reports. These statements do not fit into the theory of some, so they still speak as if their personal experiences could be generalised to everyone. Last edited by Class A; 08-04-2015 at 02:36 PM.

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07-06-2015, 03:14 PM	#121
Zafar Iqbal Veteran Member Join Date: Oct 2010 Photos: Gallery Posts: 1,187	Originally posted by rawr You have to be very aware of the AF mode settings I pondered about this and did some quick and dirty shots while on my way home from work. My initial impression: 9 point expanded AF area gave better focus. If AF-S focusing was off, then expanded AF would do the trick, or in general land the focus closer to the subject I was going for. If AF-S focusing was spot on, then expanded AF would generally be a bit off and only occasionally (only ones, actually - amongst the 70ish shots I did) wander way off. I've uploaded some of the most meaningful photos - You can see in captions, which photo used which AF mode. Click t enter album: Some of the last photos are shot using AF-S but nailed the focus on what should have been tricky? I must admit I can't really make sense of this - also, if expanded AF area indeed improves focusing and AF-S is that bad then why have AF-S? Aaan, just to repeat myself, I haven't noticed the focusing being so tricky with my other cameras though they are not same model. All photos were shot using Pentax 70mm Limited. I'm open to whatever theories you guys may have - I just want to understand what's going on so I can move on from there. Ps. photos can be viewed or downloaded in full resolution for pixel peeping. Pps. I always used center point and never recomposed.

08-03-2015, 07:55 PM - 2 Likes	#123
nicoprod Veteran Member Join Date: Nov 2010 Location: New Berlin, WI Photos: Gallery \| Albums Posts: 519	I got a used but mint copy of the 18-35 a few days ago, tested it in natural light the first day mostly at close range and was fairly satisfied with the AF. I took the risk of taking it to a wedding the following day and I was so weirded out by the AF behavior during the reception under electric light that I ended up calling the 17-50 to the rescue. The Sigma 17-50 is a decisive focuser, never readjust more than once if it ever does while the 18-35 micro adjusted often 2,3, 4 times before at times completely missing the target. I'm very much used to covering receptions in low light and the 17-50, or even better the 31 are much much more decisive than the copy of the 18-35 I got. I had another wedding the following day and left it home in favor of the 31.... I wanted to 18-35 so I can have it glued on one body and have a portrait lens on this other ( I always professionally shoot with 2 cameras). With that I was hoping to do all my indoor coverage without having to switch lens. It's not gonna happen for now. The 18-35 delivers amazing IQ but I can't afford missing money shots because of an unpredictable auto-focus. It's back in the box and being returned tomorrow.

08-03-2015, 11:24 PM	#124
Digitalis Site Supporter Join Date: Mar 2009 Location: Adelaide. Posts: 10,158	Originally posted by Zafar Iqbal What do you guys think regarding focusing accuracy? Mine is still very hit-and-miss, regardless of light levels, AF mode or AF point used.

08-04-2015, 12:41 AM - 1 Like	#125
howieb101 Veteran Member Join Date: Nov 2008 Location: Melbourne, Australia Photos: Gallery \| Albums Posts: 594	Sad. A good item on paper. In reality less so. Good that Sigma continues to innovate though. I wish Sigma could manage to make their lenses smaller though. I would like to get the Sigma 85mm F1.4 but I keep thinking I could get the relatively feather weight FA 77 F1.8. Low weight versus silent focus and faster aperture has stopped me buying either so far. No clear winner. Howie Be

08-04-2015, 12:42 AM	#126
Zafar Iqbal Veteran Member Join Date: Oct 2010 Photos: Gallery Posts: 1,187	Thanks for the replies - I have 4 weddings this week (yes) and plan on following up with my findings about the lens and camerabodies shortly after this.

08-04-2015, 02:34 AM	#127
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 10,928	Originally posted by howieb101 A good item on paper. In reality less so. Depends on whom you ask. Some people are very happy and they naturally won't come this thread to make contributions. The The Sigma 18-35 f/1.8 Art club continues to receive great submissions as well. Originally posted by howieb101 I wish Sigma could manage to make their lenses smaller though. I don't think Sigma leaves out opportunities to make their lenses smaller or lighter. I believe for the desired performance they have to be this size. The FA 77/1.8 is a marvel in terms of its size and rendering but I'm not sure how many optical compromises were made to achieve this size. I guess it could have less vignetting, if it were bigger and a more complex construction could probably address the rather heavy purple fringing. Not sure either how the corners will look like on a high-MP count FF camera. I don't think this particular design could be launched as a modern lens today anymore. Which is something I regret, because I like the FA 77/1.8 like the other FA Ltd designs and I think if Pentax will update them, we won't see the same rendering anymore because certain flaws won't be excusable anymore.

08-04-2015, 10:45 AM	#128
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 18,459	Originally posted by Class A Depends on whom you ask. Some people are very happy and they naturally won't come this thread to make contributions. The The Sigma 18-35 f/1.8 Art club continues to receive great submissions as well. People may still have significant focus failures and still make great images. The real question is keeper ratio...

08-04-2015, 11:55 AM	#129
nicoprod Veteran Member Join Date: Nov 2010 Location: New Berlin, WI Photos: Gallery \| Albums Posts: 519	Originally posted by UncleVanya People may still have significant focus failures and still make great images. The real question is keeper ratio... Yep, and for people who cover events, AF speed and accuracy is essential.

08-04-2015, 12:05 PM	#130
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 18,459	Originally posted by nicoprod Yep, and for people who cover events, AF speed and accuracy is essential. I agree. I was trying to point out that the prevalence of great images from the lens has little to do with any AF problems it might have. People may not comment because there is little they can do to help the issue or they may not have the issue - lack of a post doesn't tell us which.

08-04-2015, 01:37 PM	#131
nicoprod Veteran Member Join Date: Nov 2010 Location: New Berlin, WI Photos: Gallery \| Albums Posts: 519	Originally posted by UncleVanya I agree. I was trying to point out that the prevalence of great images from the lens has little to do with any AF problems it might have. People may not comment because there is little they can do to help the issue or they may not have the issue - lack of a post doesn't tell us which. Yes it delivers very sharp and clear photos. It's definitely sharper than the FA 31 wide open. The 31 doesn't miss though and just renders better.

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08-04-2015, 02:35 PM	#133
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 18,459	Originally posted by Class A I have seen posters explicitly state that they don't have any AF problems. That doesn't fit into the theory of some, so they still speak as if their personal experiences could be generalised to everyone. I have too - but the point made about the thread existing and many good pictures in it didn't address that. I'm stumped as to the delta between user opinions - I don't have this lens. I wanted it - I wanted it BAD... but the reports of the problems have scared me away.

08-04-2015, 02:45 PM	#134
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 10,928	Originally posted by UncleVanya I have too - but the point made about the thread existing and many good pictures in it didn't address that. Of course, keeper rate is important. But if everyone posting images made with the lens had to go through great pains to get them, we'd hear more about it, wouldn't we? If you want the lens, if I were you, I'd buy the lens from a place with a good return policy or the dedication to satisfy you as a customer.

08-04-2015, 02:49 PM	#135
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 18,459	Originally posted by Class A Of course, keeper rate is important. But if everyone posting images made with the lens had to go through great pains to get them, we'd hear more about it, wouldn't we? No that assumes everyone even posts. There are more people using the lens on Pentax than participate here or on any forum I suspect. Many suffering in silence or many happy as clams - no real way to know for sure. However the people asked about it seem to fall into one or the other camp and every review seems to have problems - that is informative. As for a return policy. No that's not going to happen for now. I am staying away. If a great review comes out showing that the problems have been resolved I will be interested. Until then - no thank you. I have many outlets for my cash...