[Edgar_in_Indy]

(I am going to read your comment as not being rudely sarcastic and snarky because you're not a rude person right?I)

I like to think not so your generous reading is appreciated. I'll admit to snarky & sarcastic but I only meant to poke fun at all of us (myself included) for our reluctance to accept the real-world trade-offs in lens design.

This is the most pathetic flame war I've ever witnessed.

[mee]

I like to think not so your generous reading is appreciated. I'll admit to snarky & sarcastic but I only meant to poke fun at all of us (myself included) for our reluctance to accept the real-world trade-offs in lens design.

I read it many times and couldn't see it being used in any other manner.. nonetheless.. I am glad to be wrong here! *hand shake*

[VoiceOfReason]

Oh just what I needed, a guy who tells me I might need both... will the LBA ever stop?

You need both.

[dadipentak]

This is the most pathetic flame war I've ever witnessed.

I wasn't paying attention during Flame 101.

[Rich M]

The tutorial is on dpreview

[Digitalis]

Well i'm on my lunch break so I'll post some initial thoughts on this lens which arrived today.

I had my Pentax K5IIs with the FA31 on hand for a comparison, so this will be my reference lens.

Construction - Very well made, by feel it is at least 300 grams heavier than than the FA31, unlike the FA31 the weight is distributed evenly. The focus throw is surprisingly short, I'm also disappointed to see that Sigma still hasn't made a pentax friendly lens cap.

Size - With the hood on it is double the size of the FA31mm f/1.8, it is also has considerably more girth to it than the FA31 does. With the lens hood on it looks about 30% smaller than a Canon EF 24-70mm f/2.8L.

Vignetting - Compared to the FA31 which has a reasonable amount of fall of towards the corners, the Sigma 18-35mm f/1.8 has to my eyes on average 2.5 stops worth of fall off in the corners - which gets progressively worse at the wide end at f/1.8, the issue is non existent by f/4.5. It is clear to me that DXO took their Lens transmission score from the very central point of this lens, rather than averaging the illumination across the relevant imaging area ( APS-C). From a flat middle grey surface filling the APS-C frame, and illuminated under 4500K lighting (Light was incident metered by a sekonic L508 for f/1.8 1/60th ISO 80). under these conditions a perfect lens transmitting all light through it should get a luminance value of 128. Under these test conditions the FA31 reproduced a mean averaged luminosity of 114.84 @ f/1.8 across the frame. The Sigma 18-35mm f/1.8 when used at the same focal length and aperture, the mean averaged luminosity was 110.29 across the frame. I'll have to get the absolute illumination figures from my test bench. ( so take these results with a hearty pinch of salt)

Distortion - On the FA31 it is only barely noticeable, on the sigma 18-35 it is obvious at 18mm and is still noticeable at 35mm. LR should be able to correct for this easily, but expect to lose about a few mm of focal length when lens corrections are applied.

Fringing - I'm a bit hesitant to say anything definitive on this subject until I get the sigma on the testing bench but from what I have seen it is well controlled at close distances, however at longer distances this lens is prone to purple/green fringing which the FA31 doesn't suffer from.

Flare - it has been really overcast today here in my city, so definitive flare tests will simply have to wait.

Resolution - Again away from my lens testing bench it is hard to give definitive numbers, the sigma 18-35mm f/1.8 is a contrasty lens and it delivers impressive amounts of detail when stopped down.

And here's the big one: Autofocus.

My FA31 has needed no AF adjustments whatsoever on the Pentax K5IIs.I tested it on my Selected contrasty AF target 4m away from me and @ f/1.8 the FA31 nailed it. The store brought in two copies of the Sigma 18-35mm f/1.8 ASPH for me to choose from. To be frank the first copy had catastrophic back focus issues. At 35mm @f/1.8 focusing on the high contrast target I had set up the lens focused nearly 10m behind it. The second copy placed the plane of focus only slightly behind my target which is well within my cameras ability to correct for. Having seen the considerable disparity in AF accuracy between the two samples of this lens I handled gives some sense as to why Sigma made the lens Dock available for the Pentax K mount.

[Class A]

Having seen the considerable disparity in AF accuracy between the two samples of this lens I handled gives some sense as to why Sigma made the lens Dock available for the Pentax K mount.

So the reason Pentax made AF adjustment a feature of their better cameras must be because all their better cameras have AF issues? Or are you saying they included that feature just for third-party lenses, because obviously a Pentax lens never has FF/BF?

Sorry, this just doesn't make sense.

As every manufacturer, Sigma produces some copies that have higher tolerances than others.

Incidentally, the FA 31/1.8 is unfortunately an example for a Pentax lens that has many "suboptimal copy" stories associated with it. A copy with a tight lens hood and inner lens groups seems to be the exception rather than the rule. Many copies have at least one of their three lens groups wobbling in some way, impacting on IQ, depending in which orientation you hold the lens. For the price the FA 31/1.8 sells, one should expect better manufacturing tolerances and/or QC.

The fact that Sigma offer a dock that allows you to fine-tune AF for different focal length and distances is a big improvement over the "one size fits all" approach of current cameras that only give you one AF-adjustment value for all scenarios. This Sigma AF-adjustment functionality deserves to be applauded.

BTW, regarding flare, I remember you constantly stating that Sigma lenses are so much worse than Pentax lenses. I just used my FA 31/1.8 in a shoot that involved shooting against the sun. It flared so bad in many shots that the images pretty much are unusable unless you really like big purple blotches all over your image. I did a quick informal comparison to my Sigma 28/1.8 EX and the latter did flare differently (more localised) than the FA 31/1.8 but not worse.

Don't get me wrong, the FA 31/1.8 is a fantastic lens, but so is the Sigma 18-35/1.8. With both, you have to make sure you have a good copy and with both you need to take care when shooting against the sun. Both provide outstanding IQ when used well.

[Digitalis]

So the reason Pentax made AF adjustment a feature of their better cameras must be because all their better cameras have AF issues? Or are you saying they included that feature just for third-party lenses, because obviously a Pentax lens never has FF/BF?

The reason why I said what I said is because it puts the pressure off sigma for adjusting their lenses for different makes of camera. This is both a good thing and a bad thing - it means that they can produce lenses out of the factory that do have horrendous issues with AF accuracy. In a nutshell: you have FF/BF issues? too bad, sigma will just tell you to get the dock (which is another $89 for Australians). Pentax cameras do FF/BF and I'm grateful for the inclusion of an adjustment, but it is designed for pentax lenses. Having said that, with the K5IIs with my FA lenses I have only had to make adjustments for one lens* out of the 20 or so FA and DA lenses I presently use.

ncidentally, the FA 31/1.8 is unfortunately an example for a Pentax lens that has many "suboptimal copy" stories associated with it. A copy with a tight lens hood and inner lens groups seems to be the exception rather than the rule.

Well my copy is an exception - I agree with you there isn't really an excuse for the sample variations we have been seeing lately.

regarding flare, I remember you constantly stating that Sigma lenses are so much worse than Pentax lenses. I just used my FA 31/1.8 in a shoot that involved shooting against the sun. It flared so bad in many shots that the images pretty much are unusable unless you really like big purple blotches all over your image. I did a quick informal comparison to my Sigma 28/1.8 EX and the latter did flare differently (more localised) than the FA 31/1.8 but not worse.

Older sigma lenses like the 100-300mm f/4 APO EX DG and 180mm f/3.5 EX (even the 180mm f/2.8 that replaced it) have been criticized for their sub par flare tolerance (compared to the reviewers reference points - typically being Canon or Nikon) the Sigma 8-16mm f/4.5-5-6 ASPH super wide has issues with flare, it is no match for the DA15mm f/4 ASPH which is very resistant to it. I have seen other reviewers test out the new 18-35mm f/.1.8 lens for flare tolerance and although i'm not overly impressed I'm convinced Sigma has made improvements in their coatings, especially taking into account that there is considerably more glass** in the sigma 18-35mm as there is in the FA31, differences in flare handling characteristics are inevitable and will boil down to taste.

Personally I never have really had any show stopping issues with flare with my FA31:


Pentax K5IIs - Pentax FA31mm f/1.8 ASPH Limited 1/640th @ f/4 ISO 80


*and that lens was the FA77 - which I put in a +1 AF adjustment, @ f/1.8 the lens seemed to be putting the plane of focus slightly behind the precise point I was aiming at.

**FA31mm f/1.8 ASPH limited has 7 elements 6 groups, Sigma 18-35mm f/1.8 ASPH has 17 elements 12 groups.

[Class A]

This is both a good thing and a bad thing - it means that they can produce lenses out of the factory that do have horrendous issues with AF accuracy.

I cannot believe that this was their thinking.

Many users won't even consider using the dock and Sigma would be facing a lot of returns if they simply relied on users fixing horrendously out-of-spec lenses. It wouldn't be a smart strategy on Sigma's behalf.

In a nutshell: you have FF/BF issues? too bad, sigma will just tell you to get the dock (which is another $89 for Australians).

Are you reporting from experience or are you just speculating?

I'm fairly sure that Sigma will look at a lens and even calibrate it for you if you ask them to, despite the existence of the dock. I have to admit that I don't really know (I only have excellent experiences with Sigma regarding lenses that precede the dock) but I'm not making a statement without expressing that I'm making an assumption.

Personally I never have really had any show stopping issues with flare with my FA31

Try moving the sun close to an edge of the frame, or just a little outside the frame.

I'm sure you can provoke the wild flaring, if you try. I'd be extraordinarily surprised if I had a copy that flared more than others.

[mrfyzv]

This is the most common variant

[Digitalis]

Sigma would be facing a lot of returns if they simply relied on users fixing horrendously out-of-spec lenses. It wouldn't be a smart strategy on Sigma's behalf.

Bear in mind that this is the same company that priced one of their top tier APS-C format cameras in the same league* as the Pentax 645D, when it was in no position at all to compete with medium format digital in the first place. Sigma has made quite a few mistakes.

I have to admit that I don't really know (I only have excellent experiences with Sigma regarding lenses that precede the dock)

I too have had excellent experiences with Sigma in regards to de-centered copies of the 8-16mm f/4.5-5.6 ASPH - which I went through nearly five copies of until sigma sent me a new lens with a letter certifying that its performance was within tolerances.

*then they proceeded to screw over their customers who bought it earlier at list price by dropping the price of the camera later on.

[Edgar_in_Indy]

the Sigma 8-16mm f/4.5-5-6 ASPH super wide has issues with flare, it is no match for the DA15mm f/4 ASPH which is very resistant to it.

A 15mm f4 prime is more resistant to flare than an 8-16mm extremely ultra-wide zoom? I would certainly hope so! It would be pretty disappointing if the prime did not best the zoom in practically every optical benchmark. Particularly when we're talking about a zoom lens that pushes the envelope in terms of wide angles, versus a prime lens that is only moderately wide.

the considerable disparity in AF accuracy between the two samples of this lens I handled gives some sense as to why Sigma made the lens Dock available for the Pentax K mount.

In regards to AF tolerances and such, it may be that Sigma and other lens makers are aiming at a moving target. I say this because when I went from my K-x to my K-30, all of my lenses required AF adjustment. I don't know if my K-x was out of spec, or my K-30 was, or if they were both out of whack, but something was definitely different between the two bodies.

Anyway, there is a reason that professionals spend good money to custom-calibrate lenses to individual bodies. The fact that Sigma offers this service for free is a huge incentive for me to go with Sigma. I have utilized their free lens-to-body calibration service a couple times in the past, and they have provided extremely fast service with perfect results. The fact that they also offer a dock, for end-user adjustment and calibration (and firmware upgrades) is a nice touch.

Although I will say that my Sigma 85mm 1.4 (which I never used on my K-x) was spot-on perfect out of the box on my K-30. And that's pretty impressive considering how ridiculously thin the focal plane can be at f1.4 and 85mm!

[bossa]

I cannot believe that this was their thinking.

Many users won't even consider using the dock and Sigma would be facing a lot of returns if they simply relied on users fixing horrendously out-of-spec lenses. It wouldn't be a smart strategy on Sigma's behalf.


Are you reporting from experience or are you just speculating?

I'm fairly sure that Sigma will look at a lens and even calibrate it for you if you ask them to, despite the existence of the dock. I have to admit that I don't really know (I only have excellent experiences with Sigma regarding lenses that precede the dock) but I'm not making a statement without expressing that I'm making an assumption.


Try moving the sun close to an edge of the frame, or just a little outside the frame.

I'm sure you can provoke the wild flaring, if you try. I'd be extraordinarily surprised if I had a copy that flared more than others.

I own the dock for Nikon and thus have been reading a few articles online about its use. I read one yesterday which stated that Sigma can only factory-calibrate your focus for one of the extreme ends of the distance scale (either close or far). It seems that The Dock is more flexible in that you can also adjust for several distances between the extremes as well as both extremes.

Personally, I would have preferred a USB port on the lenses so that the provided Software could take full control of the camera allowing a range of test shots and measurements to be taken in one hit. The software could then apply the desired settings to the lens without all bouncing back and forth currently required . I suspect that this will eventually happen but it will probably be another manufacturer that achieves this.

I find it interesting that a store would bring in two copies of a lens for someone to check out.. I think I know which store that is Doug so I won't be heading over to grab that copy you mentioned

---------- Post added 08-07-14 at 08:23 AM ----------

Bear in mind that this is the same company that priced one of their top tier APS-C format cameras in the same league* as the Pentax 645D, when it was in no position at all to compete with medium format digital in the first place. Sigma has made quite a few mistakes.




I too have had excellent experiences with Sigma in regards to de-centered copies of the 8-16mm f/4.5-5.6 ASPH - which I went through nearly five copies of until sigma sent me a new lens with a letter certifying that its performance was within tolerances.

*then they proceeded to screw over their customers who bought it earlier at list price by dropping the price of the camera later on.

How did you achieve this? Was it CRK or Sigma who certified the lens?

[Digitalis]

I own the dock for Nikon and thus have been reading a few articles online about its use. I read one yesterday which stated that Sigma can only factory-calibrate your focus for one of the extreme ends of the distance scale (either close or far). It seems that The Dock is more flexible in that you can also adjust for several distances between the extremes as well as both extremes. Personally, I would have preferred a USB port on the lenses so that the provided Software could take full control of the camera allowing a range of test shots and measurements to be taken in one hit. The software could then apply the desired settings to the lens without all bouncing back and forth currently required . I suspect that this will eventually happen but it will probably be another manufacturer that achieves this. I find it interesting that a store would bring in two copies of a lens for someone to check out.. I think I know which store that is Doug so I won't be heading over to grab that copy you mentioned

I also own the dock for F mount, and the thing that annoys me here is the lack of documentation and the fact that there is no adjustment points between 2m and infinity*. This is where AF becomes problematic for the 18-35mm f/1.8 - in the middle distances between the extremes. I too was surprised that the store brought in two copies of then lens when they had originally only had one of them on the way in. I suppose they had in mind the fiasco I had with the Sigma 8-16mm f/4.5-5.6 - I went through several copies of it to find one that was perfect. Then again I have had experiences with Canon L and Nikkor G FX format lenses that were similar - the 24-70 for instance, why is it that the big two never get those lenses right?

How did you achieve this? Was it CRK or Sigma who certified the lens?

The certification came from Sigma, I still have the letter I think.

*I noticed this in a review for the 18-35mm f/1.8

[DSims]

The big question is what has happened to the Pentax lens designers. Ricoh said it planned to rehire them. I see no evidence of that, does anyone else? Maybe they are all working on the new DF series of lenses.

I'd never heard this - I sure hope it's true! This is my #1 concern about Pentax right now - they need those guys more than anything else! The completely uninspired DA20-40 Ltd certainly doesn't look like the type of thing they'd create - I hope they are quietly working on the new ~*70-200 (and who knows what else)!


Before I get all kinds of grief for putting the DA20-40 down, it does have virtues - like small size and excellent build quality. But the photos are what I'd expect from a zoom for about half its price. Which still makes it a good lens for some people, but at that price it should've been great for almost all people. Happy owners should continue to be happy with it - it's just that I believe it should have been made to cater to the extra-picky as well.