Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-17-2015, 02:29 PM   #91
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
I received mine today and within few shots I noticed something was off. Ironically, I've seen a whole bunch of high praises towards this lens, but never seen anything about anyone having issues until today. I also simply assumed this new Art series would be an overall improvement in performance quality.


QuoteOriginally posted by sharik Quote
As the first step, I tried to quantify the frequency of correct and incorrect focusing by taking multiple photos of my "test object" (an electrical pole some 20 meters away) in series of 10 shots.
Could you please elaborate exactly how you trained your lens? In what way did the training differ from ordinary "random" focusing?

I really want this lens to work, but as it is now - about 20% keeper rate - it simply isn't useful.

06-19-2015, 01:02 PM   #92
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
I don't have any numbers on it, but I'm certain I was within the 10-20% successratio range just a day ago - since then I've been trying to "train" the lens.

I shot 182 pics today, of which 50 are out of focus. I did not confirm focus in 1:1 but instead by viewing in fullscreen. The failrate is crude, as I'm certain some of the misses were user due to error or tricky subjects.

Anyhow, from 20% succesratio to 73% is quiet a jump. I'm hoping for an even better rate.

I noticed the problem on the 18mm end from the very beginning, like many other users - I haven't shot much on 35mm, but haven't had issues with the few shots I did. Today I noticed a whole bunch of badly focused shots on the 35mm end.

I had already started the procedure with the dealer about sending the lens back and get a refund - but now I'll actually wait a bit.
06-19-2015, 02:58 PM   #93
Veteran Member
MadMathMind's Avatar

Join Date: Dec 2013
Location: Houston, TX
Photos: Gallery
Posts: 1,717
Original Poster
What aperture are you using for your shots? That tells you a lot about the failure.

Both my FA31 and FA77 miss focus ~5-10% of the time when I shoot below f/2.8. After calibrating my Sigma and getting rid of that bad battery, I've gotten my Sigma within a good ratio, although I don't keep numbers on it. Over f/2.8, I don't generally have issues with any of my lenses, Sigma included. Certain colors of dark light seem to throw it. Despite this, I was able to get a good percentage of shots in focus inside a cave, and it's got to be somewhere around 0EV or so in there. It's harder to think of a more difficult place to focus than that.

One of the best tricks when shooting at large apertures is not to recompose. I find it often leads to an out of focus subject. Instead, put what you want under a focus point and plan on cropping the fat in post.
06-19-2015, 03:53 PM   #94
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
95+ % shots are done at f.8. I shot few using smaller apertures such as f5 and smaller and have not noticed problem at these apertures - but then again, the dof increases and makes it harder to tell.

I understand the focal plane will shift when recomposing, but that's not my complaint. With the majority of the shots I've been doing, I didn't recompose simply because I'll forget what I focused on - so its just simpler to keep focusing point and target in dead center. :P

Click to enter album:


Pic 1: off center point used - no recompose. focused on top line text.
Pic 2: center point aimed at right side fences, down by the ground.
Pic 3: center point on Sisse Marie Welling poster

All these suffer front front focusing - but I do get BF as well - so far it seems random when I'll get FF or BF and how much off focus I'll be can vary as well.

06-20-2015, 10:28 AM   #95
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
Oh man, I can't decide what to do. I was at a wedding and the miss rate was very high - but I dig get plenty of well focused shots as well - and they look so frekin awesome.

This lens is so damn sharp and f1.8 @ 18mm looks incredible - when it DOES focus.

Edit: I frequently used small apertures especially for group photos and only let people go after I had pixel peeped and was satisfied - good thing I did, because there was a bunch of out of focus even at 18mm f7-8

Last edited by Zafar Iqbal; 06-20-2015 at 10:35 AM.
06-20-2015, 11:16 AM   #96
Veteran Member
MadMathMind's Avatar

Join Date: Dec 2013
Location: Houston, TX
Photos: Gallery
Posts: 1,717
Original Poster
Not that it helps you, but I never have issues at f/8. Getting a shot out of focus at f/8 at 18mm is incredibly difficult to do. The hyperfocal distance is about 7'. Focus there and entire shot should be in focus. Heck, if you focus further than 4' away, then everything in immediate range should be in focus; only the far, far background at infinity won't be.

Try setting some objects at known distances and seeing if the focusing scale on the lens matches where the object is. If you place something 6' away and it focuses at infinity or at 4', then you'll know something is very wrong.

If you're serious about the lens, you need to get the dock and see what happens. Or you need to return this lens for a new one and try it out.
06-20-2015, 12:10 PM   #97
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
I agree, and it's kind of impressive not to obtain proper focus and such focals and apertures.

I'll see if the focusing keeps improving on the lens, and fast. If not then I have to send it back.

---------- Post added 20-06-15 at 21:25 ----------

BTW, I got the dock when I first purchased the lens but I haven't used it much. I find it to be tricky when most issues are at further away distances.

I'm open for tips.

Edit: Screw this - now it's being completely rubbish. On the first day when I tried to see how the AF is, here at home during the evening, I got many out of focus shot - a day later, the ratio had improved by a lot. Now, still here at home, same light and targets, I can't get even a single shot in focus

Last edited by Zafar Iqbal; 06-20-2015 at 01:53 PM.
06-22-2015, 09:46 AM   #98
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 18,459
QuoteOriginally posted by Zafar Iqbal Quote
...now it's being completely rubbish. On the first day when I tried to see how the AF is, here at home during the evening, I got many out of focus shot - a day later, the ratio had improved by a lot. Now, still here at home, same light and targets, I can't get even a single shot in focus
That sucks. I am sorry to hear it is such a temperamental beast. I think there are a lot of other options that may not be as fast but I frankly don't understand the appeal of 18mm shots at f/1.8 myself. Landscape shots I shoot with higher f/stops, people shots tend to have depth when shot at this focal length so again I'm shooting higher f/stops. I'm not saying there is no place for it - just pointing out that the opportunities to excel with the wide end at wide open are fewer and you may get away with an alternative like the 16-50 or the 20-40 to get similar benefits.

06-22-2015, 10:27 AM   #99
Site Supporter
Site Supporter




Join Date: Mar 2009
Location: Gladys, Virginia
Photos: Gallery
Posts: 23,035
QuoteOriginally posted by Zafar Iqbal Quote
I agree, and it's kind of impressive not to obtain proper focus and such focals and apertures.

I'll see if the focusing keeps improving on the lens, and fast. If not then I have to send it back.

---------- Post added 20-06-15 at 21:25 ----------

BTW, I got the dock when I first purchased the lens but I haven't used it much. I find it to be tricky when most issues are at further away distances.

I'm open for tips.

Edit: Screw this - now it's being completely rubbish. On the first day when I tried to see how the AF is, here at home during the evening, I got many out of focus shot - a day later, the ratio had improved by a lot. Now, still here at home, same light and targets, I can't get even a single shot in focus
You need to exchange the lens and see if a different one works better. That isn't the sort of situation where a dock will help.
06-22-2015, 12:53 PM   #100
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
I think I should give it a try with the dock and see what happens. I'm not optimistic about it, but I might as well try it - I just don't have too much time on my hands

QuoteOriginally posted by UncleVanya Quote
That sucks. I am sorry to hear it is such a temperamental beast. I think there are a lot of other options that may not be as fast but I frankly don't understand the appeal of 18mm shots at f/1.8 myself. Landscape shots I shoot with higher f/stops, people shots tend to have depth when shot at this focal length so again I'm shooting higher f/stops. I'm not saying there is no place for it - just pointing out that the opportunities to excel with the wide end at wide open are fewer and you may get away with an alternative like the 16-50 or the 20-40 to get similar benefits.
It happens, but I rarely shoot stopped down. I prefer large apertures for 2 reasons, shallow depth of field and ability to lower the ISO with more than 1 stop. That's quiet a bit when I'm often out shooting at ISO 3200 or higher.

I've been using Sigma 18-50m f2.8 for the past 3-4 years and it's been OK but I've for some time wished I could use lower ISO - moe so that to have shallow depth of field. I used the 18-35 last Saturday at a wedding and it is what it I need. If only it would focus properly


QuoteOriginally posted by Rondec Quote
You need to exchange the lens and see if a different one works better. That isn't the sort of situation where a dock will help.
I think you are correct - I did some better tests today, aiming for for a target some 50 meters and noting inbetween that could distract. The focus could still and very close to the 2 meter marker on the distance level, and I think it even got below ones.

It's kind of ironic - the 18-50mm did what it was supposed to do, produced nice shots and all, but I never liked using it. The 18-35 on the other hand is a joy, even if it's bigger, but it's too darn unreliable.
06-23-2015, 07:38 PM   #101
Junior Member




Join Date: Oct 2013
Location: Canberra, Australia
Posts: 31
QuoteOriginally posted by Zafar Iqbal Quote
I received mine today and within few shots I noticed something was off. Ironically, I've seen a whole bunch of high praises towards this lens, but never seen anything about anyone having issues until today. I also simply assumed this new Art series would be an overall improvement in performance quality.

Could you please elaborate exactly how you trained your lens? In what way did the training differ from ordinary "random" focusing?

I really want this lens to work, but as it is now - about 20% keeper rate - it simply isn't useful.
Hi Zafar,
You can put the camera in the AF-C mode and move between distant and close objects several times. Or point to a featureless surface (e.g. a painted wall or a sheet of white paper) on which the system cannot focus, set the lens to infinity, and press the AF button (i have disabled the AF function on the shutter button and only use the rear AF button). The lens will change focus from infinity to minimum and back as fast as it can - this can be described as an extreme case of "hunting" that we induce and use to our benefit. You can repeat this action as many times as you want by pressing the AF button again. From my experience, after 5-10 times the lens "wakes up" a bit. Please note however that this is not an ultimate solution - the fraction of the properly focused shots increases substantially, but I could not get it close to 100% even under ideal conditions.
I'm about to send my lens to CR Kennedy for a warranty repair, with a detailed description of the AF behavior. Will keep the community posted about the outcome.
06-25-2015, 03:21 AM   #102
Veteran Member
Zafar Iqbal's Avatar

Join Date: Oct 2010
Photos: Gallery
Posts: 1,187
Thanks Sharik,

I will tuck away the Sigma and use other lenses for a while, to see if there might be anything with the camera.

I spent a good 1 hour last evening (it was still rather bright) to calibrate the Sigma using the dock - all seemed well and today a bunch of the few shots I've done so far are out of focus at medium distances (2-10 meters).
06-25-2015, 04:10 AM   #103
Loyal Site Supporter
Loyal Site Supporter




Join Date: Mar 2015
Photos: Gallery | Albums
Posts: 6,370
Wow, did I ever dodge a bullet.
06-25-2015, 05:42 AM   #104
Pentaxian
Class A's Avatar

Join Date: Aug 2008
Location: Wellington, New Zealand
Posts: 10,928
QuoteOriginally posted by pathdoc Quote
Wow, did I ever dodge a bullet.
It is very unfortunate that Zafar apparently received a copy with problems, but there is very little to suggest that you would have suffered from the same problems. Bad copies of lenses exist from every manufacturer.

Remember, we have reports from Sigma 18-35/1.8 users, such as:
"I've had this lens glued to my K-3 for weeks now. I think the lens is nothing short of fantastic, and I have had no AF problem with it at all. One other Pentax user I know has the lens and she too reports no AF issues with it."
and LensRentals is offering the Sigma 18-35/1.8 for Canon for renting.

Do you think the many happy users of the lens are the exceptions and that LensRentals would rent out a lens that cannot focus?

It is unfortunate that those who have experienced issues with the lens never engaged in a conversation with Sigma proper, supplying sample images, explaining their procedures, etc. Perhaps Zafar can achieve something to this effect. Perhaps he will just get his copy exchanged for one that works properly, which would be fine by me as well.
06-25-2015, 06:23 AM   #105
Loyal Site Supporter
Loyal Site Supporter




Join Date: Mar 2015
Photos: Gallery | Albums
Posts: 6,370
QuoteOriginally posted by Class A Quote
Bad copies of lenses exist from every manufacturer.
Perhaps they do, and I don't deny the happy users their joy, but the fact that the forum review encountered the same problem in multiple copies of the lens, that multiple users have noted the same issue and been forced to workarounds that should not have been necessary, and that this thread is as long as it is, indicates to me that the Sigma 18-35 f/1.8 Art lens is NOT a reliable or consistent performer in Pentax K mount. This is especially germane given the problems reported with other wide-aperture Sigma Art lenses since I first heard about the travails suffered by this one.

Given that I live at least 400km from the nearest dedicated bricks-and-mortar camera store and would have had to expend a LOT on postage trying to get a bad copy serviced or replaced, the whole sorry tale told by too many users indicates to me that this was a risk that was better not taken. If I ever get a chance to buy one from a bricks-and-mortar store that I can go to THE VERY NEXT DAY for a full refund if there are any issues, I may take a chance. Otherwise, no way.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
af, aperture, art, art focus issues, f/1.8 art focus, ff, focus, issue, issues, k-5, k-mount, lens, lenses, pentax, pentax lens, shots, sigma, sigma 18-35 f/1.8, slr lens, thread
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
The Sigma 18-35 f/1.8 Art club scratchpaddy Lens Clubs 112 11-29-2018 05:05 AM
Sigma 18-35 1.8 art vs HD DA 20-40mm F2.8 - 4 Limited DC WR jrcastillo Pentax SLR Lens Discussion 111 09-22-2015 03:02 PM
Sigma ART 18-35 1.8 and K-30 jrcastillo Pentax K-30 & K-50 36 07-28-2014 09:42 AM
Sigma 18-35 f/1.8 vs the Pentax DA 16-50 f/2.8 someguy42 Pentax SLR Lens Discussion 9 12-06-2013 12:02 AM



All times are GMT -7. The time now is 09:48 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top