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LFLee · 07-03-2014, 08:12 AM

Hi all...

now that Sigma 18-35 f1.8 for Pentax is shipping, and samples have shown that it has two "flaws": 1. flare resistance is so so; 2: onion ring bokeh.

I would like to know how auto focus perform on this lens? AF is something body+lens issue...
Please state the camera you use.

I have really frustrating auto focus experience with my DA*16-50 in shaded area (like shooting people in forest. under shaded tree), it always focus to the background instead of person (on K5 and K5IIs) .... Really got me crazy!

before you doubt.... I know how to get focus right (edit: at least I think I do), as there are only few bad AF instances in good lighting situations.

Thanks for sharing your experience.

Lee

Last edited by LFLee; 07-03-2014 at 10:30 AM.

**Digitalis** · 07-03-2014, 08:32 AM

I have had an opportunity to use this lens on the Canon 7D and yes, there was some inconsistency with the AF even with the center AF point.

The lens needed some micro-adjustment, but after this was done the inconsistency in AF was reduced.

DennisH · 07-03-2014, 08:37 AM - **2 Likes**

Is this a pre-emptive complaint thread?

DSims · 07-03-2014, 09:02 AM

So you mean the DA*16-50 does this even with a fixed AF point? I guess I don't shoot in those conditions much. I have the same camera and lens, but I use other lenses more frequently.

LFLee · 07-03-2014, 09:28 AM

Originally posted by DSims

So you mean the DA*16-50 does this even with a fixed AF point? I guess I don't shoot in those conditions much. I have the same camera and lens, but I use other lenses more frequently.

Yes, with center AF point. I usually half-press to AF, then turn AF dial to MF (with left hand, on K5 and K5IIs), and press again to shoot.

---------- Post added 07-03-2014 at 12:31 PM ----------

Originally posted by DennisH

Is this a pre-emptive complaint thread?

care to be elaborate? reg the Sigma lens or?

I wrote "flaws", which mean could be for some people, but not for some. and not very good flare resistance and onion ring bokeh are both shown in sample images taken with this lens.

I am planning to get this lens to replace my DA*16-50, and so want to know how it performs on Pentax body.

panoguy · 07-03-2014, 09:35 AM

Not sure how the f/1.8 aperture of the Sigma is going to vastly improve your Pentax AF in the woods, compared to the f/2.8 of the DA*... sounds more like an issue with the size of the AF points.

My 18-35 sits on a Sigma SD1, which has an AF module that is K10D-vintage, both in terms of speed and precision (ie: not too great). My K-3 is far more capable in low light and confusing environs than my K-5, but I won't be getting the 18-35 in K-mount for a while, despite how nice it is on a Foveon, so I hope another post comes along with all the info you want to read.

DSims · 07-03-2014, 09:47 AM

Originally posted by LFLee

Yes, with center AF point. I usually half-press to AF, then turn AF dial to MF (with left hand, on K5 and K5IIs), and press again to shoot.

Thanks for the clarification.

Originally posted by panoguy

My K-3 is far more capable in low light and confusing environs than my K-5

And the K-5 IIs is already better than the K-5, which was why I found the problem surprising and a bit confusing.

But it's a great question if Lee's planning to replace his DA*16-50 with it.

devorama · 07-03-2014, 01:54 PM

Originally posted by LFLee

Yes, with center AF point. I usually half-press to AF, then turn AF dial to MF (with left hand, on K5 and K5IIs), and press again to shoot.

I know this is a bit off topic, but you may want to try:

https://www.pentaxforums.com/forums/38-photographic-technique/236970-perfect-focus-everytime.html

reeftool · 07-04-2014, 05:49 AM

The lens reviews I have read mentioned some difficulty in nailing the focus at f/1.8 on Canon bodies. The DP review described it as "hit or miss" in low light and with low contrast subjects. I have seen some comments around that the Nikon version performs better in regards to AF. It wasn't a bad enough issue to flag the lens by the reviewers. We really have to wait and see how the Pentax version performs and now that the lens is finally here, I'm sure it won't be long.

Zinaone · 07-06-2014, 03:26 PM

I got my sigma 2 days ago . Im using k30 and for the first impresion it is a great companion for k30. Havent seen any focus issues. It hasnt been a long time since I got the lens and not many pictures have been taken with it so I cant tell 100%. For now Ive got some stunning resaults .

**Digitalis** · 07-06-2014, 10:21 PM

I have done a brief and somewhat rushed look at this lens today and from what I have seen there is certainly some potential in this lens.

07-03-2014, 08:12 AM	#1
LFLee Veteran Member Join Date: Aug 2009 Location: Southern California Photos: Gallery \| Albums Posts: 2,292	Autofocus on Sigma 18-35 f1.8 lens Hi all... now that Sigma 18-35 f1.8 for Pentax is shipping, and samples have shown that it has two "flaws": 1. flare resistance is so so; 2: onion ring bokeh. I would like to know how auto focus perform on this lens? AF is something body+lens issue... Please state the camera you use. I have really frustrating auto focus experience with my DA16-50 in shaded area (like shooting people in forest. under shaded tree), it always focus to the background instead of person (on K5 and K5IIs) .... Really got me crazy! before you doubt.... I know how to get focus right (edit: at least I think I do), as there are only few bad AF instances in good lighting situations. Thanks for sharing your experience. Lee Last edited by LFLee; 07-03-2014 at 10:30 AM.*

07-03-2014, 08:32 AM	#2
Digitalis Site Supporter Join Date: Mar 2009 Location: Melbourne, Victoria Photos: Gallery Posts: 11,694	I have had an opportunity to use this lens on the Canon 7D and yes, there was some inconsistency with the AF even with the center AF point. The lens needed some micro-adjustment, but after this was done the inconsistency in AF was reduced. Last edited by Digitalis; 07-03-2014 at 06:27 PM.

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07-03-2014, 08:37 AM - 2 Likes	#3
DennisH Pentaxian Join Date: Jun 2008 Location: Stratford, CT Photos: Gallery Posts: 730	Is this a pre-emptive complaint thread?

07-03-2014, 09:02 AM	#4
DSims Veteran Member Join Date: Sep 2009 Location: Southern California Photos: Gallery \| Albums Posts: 3,236	So you mean the DA*16-50 does this even with a fixed AF point? I guess I don't shoot in those conditions much. I have the same camera and lens, but I use other lenses more frequently.

07-03-2014, 09:28 AM	#5
LFLee Veteran Member Join Date: Aug 2009 Location: Southern California Photos: Gallery \| Albums Posts: 2,292 Original Poster	Originally posted by DSims So you mean the DA16-50 does this even with a fixed AF point? I guess I don't shoot in those conditions much. I have the same camera and lens, but I use other lenses more frequently. Yes, with center AF point. I usually half-press to AF, then turn AF dial to MF (with left hand, on K5 and K5IIs), and press again to shoot. ---------- Post added 07-03-2014 at 12:31 PM ---------- Originally posted by DennisH Is this a pre-emptive complaint thread? care to be elaborate? reg the Sigma lens or? I wrote "flaws", which mean could be for some people, but not for some. and not very good flare resistance and onion ring bokeh are both shown in sample images taken with this lens. I am planning to get this lens to replace my DA16-50, and so want to know how it performs on Pentax body.

07-03-2014, 09:35 AM	#6
panoguy Pentaxian Join Date: Sep 2007 Location: Washington, D.C. Photos: Gallery \| Albums Posts: 3,327	Not sure how the f/1.8 aperture of the Sigma is going to vastly improve your Pentax AF in the woods, compared to the f/2.8 of the DA*... sounds more like an issue with the size of the AF points. My 18-35 sits on a Sigma SD1, which has an AF module that is K10D-vintage, both in terms of speed and precision (ie: not too great). My K-3 is far more capable in low light and confusing environs than my K-5, but I won't be getting the 18-35 in K-mount for a while, despite how nice it is on a Foveon, so I hope another post comes along with all the info you want to read.

07-03-2014, 09:47 AM	#7
DSims Veteran Member Join Date: Sep 2009 Location: Southern California Photos: Gallery \| Albums Posts: 3,236	Originally posted by LFLee Yes, with center AF point. I usually half-press to AF, then turn AF dial to MF (with left hand, on K5 and K5IIs), and press again to shoot. Thanks for the clarification. Originally posted by panoguy My K-3 is far more capable in low light and confusing environs than my K-5 And the K-5 IIs is already better than the K-5, which was why I found the problem surprising and a bit confusing. But it's a great question if Lee's planning to replace his DA*16-50 with it.

07-03-2014, 01:54 PM	#8
devorama Veteran Member Join Date: Apr 2009 Location: Chicago, IL Photos: Gallery \| Albums Posts: 638	Originally posted by LFLee Yes, with center AF point. I usually half-press to AF, then turn AF dial to MF (with left hand, on K5 and K5IIs), and press again to shoot. I know this is a bit off topic, but you may want to try: https://www.pentaxforums.com/forums/38-photographic-technique/236970-perfect-focus-everytime.html

07-04-2014, 05:49 AM	#9
reeftool Pentaxian Join Date: Dec 2007 Location: Upstate New York Photos: Gallery \| Albums Posts: 9,555	The lens reviews I have read mentioned some difficulty in nailing the focus at f/1.8 on Canon bodies. The DP review described it as "hit or miss" in low light and with low contrast subjects. I have seen some comments around that the Nikon version performs better in regards to AF. It wasn't a bad enough issue to flag the lens by the reviewers. We really have to wait and see how the Pentax version performs and now that the lens is finally here, I'm sure it won't be long.

07-06-2014, 03:26 PM	#10
Zinaone New Member Join Date: Jan 2014 Posts: 6	I got my sigma 2 days ago . Im using k30 and for the first impresion it is a great companion for k30. Havent seen any focus issues. It hasnt been a long time since I got the lens and not many pictures have been taken with it so I cant tell 100%. For now Ive got some stunning resaults .

07-06-2014, 10:21 PM	#11
Digitalis Site Supporter Join Date: Mar 2009 Location: Melbourne, Victoria Photos: Gallery Posts: 11,694	I have done a brief and somewhat rushed look at this lens today and from what I have seen there is certainly some potential in this lens.

Autofocus on Sigma 18-35 f1.8 lens

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