[candgpics]

Hi:

I have been playing around with my new Sigma 18-35 for the last couple of days. I have only had a few minutes here and there to use the lens, but inconsistent focusing appears to be taking place. At least from just taking pictures around the house of our children, dog, and a few outdoors--I am getting both back and front focus, and it seems random.

I only shoot RAW, center focus, fully manual. I adjusted (-2), but that did not seem to solve things after I had a look at a 100 or so pictures.

I called Sigma and spoke to a technician who was very nice and spent some time on the phone with me.

Though my knowledge of optics is minimal the technician made what I thought were some interesting comments. I am paraphrasing, but he told me that DSLR cameras are using an “ancient" focusing system and are often not able to handle new “esoteric” lenses, such as the 18-35. He mentioned, though I did not quite grasp it all, the difficulty the mirror in a traditional DSLR system introduces to focusing. He also noted, after I mentioned that I turned shake reduction off, that the sensor assembly due to its shake reduction capability still causes a problem.

I did not ask why then is the lens not a mirrorless-only lens, but he assured me that absent a malfunctioning copy, I should be able to calibrate the lens and that the USB dock, if necessary, would address any additional needed calibration—and, that the lens would work at distances and focal lengths which were different than those in the calibration software. He was adamant about this (contrary to the follow-up pentaxforums testing).

I explained that I did not purchase the USB dock, as I was hoping not to have to purchase a the dock if I already had an acceptably performing lens.

I mentioned briefly the pentaxforums testing, along with the follow-up analysis on the focusing issue.

I did not go into detail about the pentaxforums testing, but did briefly mention the findings. I got the sense, but cannot be sure, that Sigma is aware of the reported autofocusing issue, but disagrees there is a problem.

Essentially, I was told—but I may not have understood everything since the discussion was somewhat technical—that “most people are not calibrating the lens correctly.”

I was specifically told to set the lens up at 1 meter distance at 35mm, at 1.8 and focus on a 3D item, not a chart. This sounds much like the follow-up testing pentaxforums did, but I will give it a try.

I do not necessarily mind buying the USB dock, though having to purchase an item, in order to make a previously purchased "pricey" item work is kind of off-putting.

I was told, and I knew this already, that Sigma will calibrate the lens and my camera for free (of course, I have three camera bodies--a K3 and two K5ii bodies-not sure how that would work, especially if firmware in the lens would be changed).

When the lens is on, it is quite sharp and aberrations are minimal/within reason (even wide open). It also renders quite nicely. At 1.8 it is sharp and smooth at the same time--kind of like very sharp, but not "digitally" sharp; more like "film" sharp, if that makes sense. As Barbara would say, "like buttah."

I'll follow up as I have time to use the lens.

[Ole]

Sadly, this lens cannot autofocus reliably and adjusting it using the USB dock won't help. It cannot be callibrated. We have gone through several copies before daring to state these facts. Sigma needs to look inwards and fix the firmware in the lens (or market it as a manual focus lens).

Sigma 18-35mm Autofocus: A Second Look - Previews and Reviews | PentaxForums.com

[MadMathMind]

I did not go into detail about the pentaxforums testing, but did briefly mention the findings. I got the sense, but cannot be sure, that Sigma is aware of the reported autofocusing issue, but disagrees there is a problem.

To quote The Music Man, either they are averting their eyes from a situation they do not wish to acknowledge or don't realize the caliber of disaster indicated by the presence of a pool hall in their community.

If this is true, then I think we've seen our last Sigma lens for K-mount. If the problem were widespread as reports on the forum are, then these would have been returned by the truckload. If that's not the case, then they haven't sold any of these in K mount and will probably not bother in the future. In fact, if they have major issues, they may not release future lenses for fear of a repeat of this. If sales are not brisk, it won't be worth the risk.

Though my knowledge of optics is minimal the technician made what I thought were some interesting comments. I am paraphrasing, but he told me that DSLR cameras are using an “ancient" focusing system and are often not able to handle new “esoteric” lenses, such as the 18-35. He mentioned, though I did not quite grasp it all, the difficulty the mirror in a traditional DSLR system introduces to focusing. He also noted, after I mentioned that I turned shake reduction off, that the sensor assembly due to its shake reduction capability still causes a problem.

I assume he means the f/2.8 limitation? If he's complaining about PDAF...well, no one has a way to do CDAF through an optical viewfinder yet. Remove that ability and you don't have an SLR anymore.

The sensor has no effect on autofocus through the viewfinder. Either he's got it wrong or you misunderstood what he said. As a result, whether SR is on or off will have precisely zero effect on autofocus through the viewfinder. (Through live view...not sure, but that uses the sensor at least.) Or he was talking about the beam splitting. But a 1.8 lens has about 70% more light throughput than a 2.8 lens, so splitting that in half is still more than most lenses manage.

All things said, there do exist functioning copies of this lens. I have one. There seems to be a few more on the forums here.

[candgpics]

Hi:

Thank you for the comments. Regarding the shake reduction, he may have been referring to live view. I do not recall him making that distinction--but I might be mistaken.

I wonder how there are properly functioning copies of the lens--and by that i mean accurate focus at 1.8. Being able to use the lens at 1.8 is the raison d'être of the lens, at least for me.

To carry the bulk and volume of the lens and not use it at 1.8 would seem an unnecessary task, though, I understand it is a sharp lens and relatively aberration free--when in focus.

Using the lens at 2.8 or narrower under circumstances which mask the focusing error due to the increased depth of filed is something in which I am not interested.

I often take pictures indoors under moderately to dim lighting conditions during MMA/BJJ, and fitness events. I purchased this lens to further limit my need of flash.

So, I will give it the old college try with some more calibration. I might try the USB dock, but I also might re-read the pentaxforums follow-up testing and realize the die has been cast and I need to look for a different lens to fulfill my needs.

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Last edited by candgpics; 02-17-2015 at 07:48 PM.

[DDoram]

My Sigma 18-35 works well and I feel it may be an exaggeration to imply that all 18-35 lenses are bad. It is a great lens optically but somewhat slow to get Af confirmation.

[calsan]

Why can my ancient FA 50 f/1.4 lens focus acceptably with PDAF?

[MadMathMind]

It's a bit too much to go through all my photos to look for ones at f/1.8, but I know there's a bunch in here:
https://www.flickr.com/photos/madmathmind/sets/72157649935290658/
https://www.flickr.com/photos/madmathmind/sets/72157649966736798/

Focus is pretty good, but do keep in mind that it was unspeakably dark in the cave. Like, so dark that I couldn't see what was in focus at all. I relied on the camera 100%. Keeper rate was not that high (and you can see focus failed on some of the shots I did keep), but it was probably near -3EV mark for most shots. I wouldn't be surprised that for the shots that did fail, no lens would have focused reliably.

So I'd say copies that focus at f/1.8 do exist and mine does ok at the least. I usually go around f/2. Feel free to poke around though here for some large aperture shots:
https://www.flickr.com/photos/madmathmind/sets/72157649140156878/

[Paul the Sunman]

My Sigma 35mm f1.4 Art also focuses perfectly on the K3, and it presumably uses similar technology to the 18-35.

[candgpics]

Madmathmind I am on my phone now, but will look at your photos later. Thank you.

I contemplated getting the Pentax 20-40, as I have been looking for a general travel lens for an upcoming trip this summer. I just felt 20 was not wide enough and though the Sigma is not tremendously wider, 2 mm is not insignificant. And I felt the 1.8 feature would allow me to use the lens for my mma/bjj and fitness work. I currently have the Sigma 24 1.8. It's got its issues (perhaps some very slight softness in the upper left/central corner) and it focuses loudly, but it is a sweet lens and more than sharp enough at 1.8.

It feels like such a let down to get a pricey toy (if I keep it, though, a couple of lenses will get sold to pay for it) and for it not to work correctly, particularly since it is sharp across the frame at 1.8 at all focal lengths when the focus is accurate.

[rawr]

Unlike the Sunman, my Sigma 35 f1.4 shares some of the same issues as the 18-35. Inconsistent AF. Reportedly with Nikon bodies as well, although not so much (it seems) with Canon.

The various Sigma teams (optical, AF mechanism, and firmware) need to work more closely together. The Sigma optics with the new designs are often great, but the supporting systems like AF and firmware don't seem to be integrated properly.

[calsan]

I felt the 1.8 feature would allow me to use the lens for my mma/bjj and fitness work

By which you mean carrying the lens will make you fit??? :-) I wouldn't call it a travel lens, but I'm pretty skinny. Maybe a more muscular person would carry it all day around the neck.

[VoiceOfReason]

I got really lucky with my copy on both my K3 and K5. I haven't tried it on my K-01.

[Digitalis]

explained that I did not purchase the USB dock, as I was hoping not to have to purchase a the dock if I already had an acceptably performing lens.

That was your first mistake - Sigma lenses are notorious for AF calibration issues. The lens dock is a critical tool for getting this lens to work properly across multiple camera bodies.

[Driline]

Sadly, this lens cannot autofocus reliably and adjusting it using the USB dock won't help. It cannot be callibrated. We have gone through several copies before daring to state these facts. Sigma needs to look inwards and fix the firmware in the lens (or market it as a manual focus lens).

Sigma 18-35mm Autofocus: A Second Look - Previews and Reviews | PentaxForums.com

Thank you for the Second Look Review of the Sigma 18-35 lens. It was one of the main reasons I purchased a used copy of the Pentax FA 31 for the same price as a new Sigma. I have been very happy with that decision.

[Rondec]

I'm afraid Sigma's whole line about fast lenses not working well with modern PDAF systems is just crazy. I have a whole bunch of lenses (DA *55, FA 31, FA 55) that are faster than that and have no trouble with focus accuracy on either a K3 or K5 II. The fact that this Sigma lens does (even if it works with CDAF) is problematic from Sigma's standpoint. Blaming the camera is the easy out, but then why don't other lenses have problems?