[Driline]

I appreciate the effort, but I find the four pictures to be too different to be able to glean much from the comparison.

Perhaps he should stuff the cat so it doesn't move around

[normhead]

I appreciate the effort, but I find the four pictures to be too different to be able to glean much from the comparison. I certainly prefer the composition, and brighter exposure of the Rokinon shot, as well as having the subject closer to the camera to throw more of the background into a softer focus, but I don't think that really says much about the respective lenses.

I have to agree with the above... the Sigma image also appears to have sharpening artifacts, not to mention that half the images are taken @ ƒ1.4 and half @ƒ3.2. But aside from that, the Rokinon looks soft, and the 85, I think you might have motion blur, I can't find anywhere in the image in clear focus. I am impressed with the F 50 1.4, given the variety of images and positions, in this series of images, I'd give it top marks... but i wouldn't predict it would come out on top on the next series. but it is up 1-0-0-0- if you're keeping score. At least in my book.

[Mirton]

I have to agree with the above... the Sigma image also appears to have sharpening artifacts, not to mention that half the images are taken @ ƒ1.4 and half @ƒ3.2. But aside from that, the Rokinon looks soft, and the 85, I think you might have motion blur, I can't find anywhere in the image in clear focus. I am impressed with the F 50 1.4, given the variety of images and positions, in this series of images, I'd give it top marks... but i wouldn't predict it would come out on top on the next series. but it is up 1-0-0-0- if you're keeping score. At least in my book.

The Sigma 30mm was shot at f3.5 https://www.flickr.com/photos/22728984@N04/14311278401/in/photostream/
The Rokinon was shot at f1.4 (or maybe f2.0, the aperture was stuck semi-wide at the time unbeknownst to me, the exif says f3.5 but it's not relevant)https://www.flickr.com/photos/22728984@N04/14311278521/in/photostream/

Sigma 85mm shot at f3.2 1/80 shutter https://www.flickr.com/photos/22728984@N04/14128089617/in/photostream/
Pentax -F 50mm shot at f3.2. 1/60 https://www.flickr.com/photos/22728984@N04/14311278181/in/photostream/

The Rokinon 35mm f1.4 UMC is an extremely capable performer (some review sites compare it favorably to the Distagon) but that's for another thread.

[Nicolas06]

I appreciate the effort, but I find the four pictures to be too different to be able to glean much from the comparison. I certainly prefer the composition, and brighter exposure of the Rokinon shot, as well as having the subject closer to the camera to throw more of the background into a softer focus, but I don't think that really says much about the respective lenses.

No offence but I'am in the same case as you! i have difficulties to really see difference in color/bokeh whatever that do not look like explained from the different focal lens, subject distance or light.

[Class A]

I wasn't aware that Sigma uses inferior glass as a cost saving measure, It's good to know.

It would be good to know if it were true.

AFAIC, it is just plain and utter rubbish. I'm sorry for the crude language, but I'm irritated by the unfounded Sigma bashing.

The 30mm F1.4 DC HSM Art has 9 lens elements in 8 groups compared to the 7 lens elements in 7 groups of the Sigma 30mm F1.4 EX DC. That is hardly an example for "cost cutting".

It is simply a different design that offers better optical performance with less exotic glass elements. Canon and Nikon would pay money to get the ecstatic press the Sigma 18-35/1.8 has received. It seems unlikely that the same company that is able to produce the world's fastest APS-C zoom that receives glowing reviews, suddenly decides to produce a cheap and optically inferior successor to the Sigma 30/1.4 EX.

Granted, the newer lens design has only one aspherical lens element (Pentax lenses like the FA 50/1.4 have none) and is missing the SLD and ELD elements from the earlier version, but its MTF chart shows extremely improved performance, particularly towards the edges of the frame. I'm not sure whether Digitalis is actually commenting on the new Art version; he may be confusing it with the older lens.

Please take comments from Digitalis on Sigma lenses with a grain of salt.

@Digitalis:
On the one hand, according to you Sigma QC is terrible, Sigma lens designers are morons, your Sigma 180mm macro apparently sucks at non-macro distances, Sigma coatings are bad (causing excessive flare), etc., the list goes on.

Yet, you have at least four Sigma lenses and they seem to be better than anything else that money can buy, given your apparent large funds for photography (including expensive Leica gear).

I really don't get why are using every opportunity to bash Sigma.

It is true that the outstanding Sigma 100-300/4 does not have a focus limiter but the Pentax 60-250/4 does not have one either and I haven't seen anyone (including you) call the designer of the 60-250/4 a "moron".

It is true that some Sigma lenses flare, but so do Pentax lenses. In a quick comparison, my FA 31/1.8 flared more than my Sigma 28/1.8/EX.

It is true that some copies of Sigma lenses come with decentering issues, but Pentax QC is not one bit better. The Pentax 16-50/2.8 has developed a bad reputation for decentering (lets not touch the SDM debacle), forum user robgo2 tried five copies of the DA* 55/1.4 and could not find one that focussed well on his K-7, and there are many copies of the FA 31/1.8 with loose lens groups giving rise to subpar performance. The list of Pentax QC issues could be easily continued.

AFAIC, it is not adequate to constantly question Sigma's QC, given the standard set by other manufacturers like Pentax.

Thank's Digitalis, I wasn't aware of major quality control issues, these lenses are just coming out now and there's not a lot of user feedback as of yet.

As you can see from above, unfortunately, consumer lenses come with their share of issues. Just buy from a reputable seller and return copies until you get a good one.

There is absolutely no reason to be more concerned with Sigma QC than with Pentax QC, for instance.

I've read that Sigma doesn't licence the AF algorithms from the other manufactures but reverse-engineers them, which might explain why there's so many AF issues with their lineup.

Lenses do not contain AF algorithms.

The camera body is responsible for determining the best focus setting.

Lenses do still have an influence on AF through various factors, one of them being the AF adjustment tables stored in the flash memory of a modern lens. If this table is not matched to the tolerance of a particular camera body, it will lead to focus errors and will have to be updated (to work with this particular camera body).

Sigma is unique in that it allows users to modify the AF adjustment tables in the lens memory through a computer (by using their Sigma dock).

With other lenses -- and they all may need adjustment, independently of the manufacturer -- you have to send them in to a service centre. Typically, the service centre does not do more than adjust the values in the lens memory. Actually calibrating lens elements would be way too costly for a simple AF adjustment and most lens constructions wouldn't support it anyhow.

To get back on topic:

I love my FA 31/1.8. It has truly unique rendering. All of the three FA Limited lenses are one of the best reasons to be a Pentax shooter.

Having said that, only you can decide which type of rendering and lens characteristics you like. I would suggest to browse Flickr, filtering for "FA 31/1.8" or "Sigma 30/1.4 Art" and decide for yourself which kind of image rendering you prefer most.

I personally stopped fretting about sharpness and corner performance, CA, etc. If I were concerned about purple fringing, etc. I would have to reject a lot of Pentax lenses, including Limited lenses. However, I now look at the big picture and ask myself whether the images produced by the lens evoke a kind of feeling that I like. The actual difference in the evoked feeling between two lenses can be small and subtle and you won't find it pixel peeping at a 100% magnification, but AFAIC at a subconscious level it is quite real and significant.

That's why I spend quite a bit of money on a FA 31/.1.8 (making sure it is not one of the many copies with loose internal lens groups).

[Pioneer]

Well spoken Class A.

Personally I have completely given up evaluating my lenses on my computer screen. I find it far more effective to evaluate a print. I use the computer screen to make my adjustments in PP and then print an 8x10 to establish how to move forward. After a time of doing this type of soft-proofing I begin to understand what my lenses look like on paper. One of the reasons I adore my FA31 is that it produces excellent prints with less computer manipulation than a lot of my other lenses.

But my tastes are not your tastes. Every photographer needs to determine what he/she likes and how a given lens works. What does the end result look like on paper? Until you start evaluating your prints on paper you may as well just shoot your camera phone and quit wasting your money.

[Digitalis]

it is just plain and utter rubbish. I'm sorry for the crude language, but I'm irritated by the unfounded Sigma bashing. The 30mm F1.4 DC HSM Art has 9 lens elements in 8 groups compared to the 7 lens elements in 7 groups of the Sigma 30mm F1.4 EX DC. That is hardly an example for "cost cutting". It is simply a different design that offers better optical performance with less exotic glass elements. Canon and Nikon would pay money to get the ecstatic press the Sigma 18-35/1.8 has received. It seems unlikely that the same company that is able to produce the world's fastest APS-C zoom that receives glowing reviews, suddenly decides to produce a cheap and optically inferior successor to the Sigma 30/1.4 EX.

The newer design is using more glass to compensate for optical errors that could be effectively countered by using a single ED, UD or Aspherical lens element. More glass in a lens leads to typically worse flare tolerance, and also increases optical complexity to counter additional problems caused by the addition of extra lens elements. It is interesting to see that lens tests have made it apparent that the sigma 18-35mm f/1.8 lens has equal or better resolution and contrast across the frame @ 30mm compared to both new and old versions of the sigma 30mm f/1.4.

Please take comments from Digitalis on Sigma lenses with a grain of salt.

I expect people to take all opinions posted on online forums with a grain of salt.

@Digitalis: On the one hand, according to you Sigma QC is terrible, Sigma lens designers are morons, your Sigma 180mm macro apparently sucks at non-macro distances, Sigma coatings are bad (causing excessive flare), etc., the list goes on.

I also shoot Nikon and Canon at work. I have never explicitly said Sigma lens coatings are bad - they decidedly average when taking into account similar lenses with similar optical specifications from other manufacturers. I have experienced a number of issues that have arisen with new lenses from Canon and Nikon. I don't think it is relevant to discuss them on a Pentax camera forum, but on other sites I have made my annoyance clear that going through six copies of the Canon 24-70mm f/2.8 L or two copies of the Nikkor 70-200mm f/2.8G that suffered from optical or operational faults that were unacceptable in a brand new lens.

Yet, you have at least four Sigma lenses and they seem to be better than anything else that money can buy, given your apparent large funds for photography (including expensive Leica gear).

The number of sigma lenses I own is closer to 14, across 3 systems: Pentax, Canon and Nikon. I bought sigma because there was simply no alternative that offered equivalent performance in that particular lens mount. However, I will also mention Half of them have needed to be exchanged/repaired due to optical faults or electromechanical failures. I have had the HSM motor burn out on a sigma 85mm f/1.4 (Nikon mount) and 50mm f/1.4 (Canon EF mount). But to be fair I have had failures occur with high end photographic equipment I have worked with: I have had a Leica Tri-elmar permanently seize up on me in unusually cold weather. It was sent to the Leica factory in Solms and repaired, free of charge. I have had the front cell of a Hasselblad HC 50-110mm f/3.5-5.6 zoom lens fall out - Hasselblad repaired the lens, and issue a recall to prevent this problem from affecting other users (which unfortunately, it did). I have had a new Pentax SMCP-FA77mm f/1.8 literally fall apart in my hands (the FA77 was the first FA limited lens I ever bought - it was repaired free of charge).

really don't get why are using every opportunity to bash Sigma.

I admit I have made my annoyance apparent at sigma more than once, but only to give a fair warning for people to be vigilant for faults when buying lenses.

It is true that the outstanding Sigma 100-300/4 does not have a focus limiter but the Pentax 60-250/4 does not have one either and I haven't seen anyone (including you) call the designer of the 60-250/4 a "moron".

I don't have any experience with the Pentax DA*60-250mm f/4 ED [IF] SDM - from what I hear it is an optically excellent albeit slow focusing lens. I'm unaware of how this lens handles in difficult lighting in regards to AF lock behavior but considering my experience with Pentax DA, and FA lenses on my Pentax K5IIs I would think the AF would have greater reliability and accuracy than what I have experienced with sigma lenses.

it is true that some Sigma lenses flare, but so do Pentax lenses. In a quick comparison, my FA 31/1.8 flared more than my Sigma 28/1.8/EX.

Flare is a rather relative and subjective thing, sometimes one individual may consider it "artistic" while another individual would throw the image in the recycle bin - I refrain from making any specific complaints about flare handling - But I will point out how a lens behaves in a worst case scenario, and regarding flare tolerance I admit I tend to generalize a bit in this regard.

It is true that some copies of Sigma lenses come with decentering issues, but Pentax QC is not one bit better. The Pentax 16-50/2.8 has developed a bad reputation for decentering (lets not touch the SDM debacle), forum user robgo2 tried five copies of the DA* 55/1.4 and could not find one that focussed well on his K-7, and there are many copies of the FA 31/1.8 with loose lens groups giving rise to sub-par performance. The list of Pentax QC issues could be easily continued.

That is rather slippery statement: the Pentax DA*16-50mm f/2.8 ED AL [IF] SDM is actually a Tokina lens - so who is really to blame for the de-centering issues? The SDM issues I have personally never experienced but I on other camera systems I too have experienced issues with AF motors. The DA*55mm f/1.4 mis-focusing on a K7 I don't really consider to be all that problematic, the K7 has the capability to adjust AF for individual lenses.The only circumstance where I would consider this to be an egregious lens blooper would be where all the lenses tested were so far out of whack no amount of AF adjustment could bring it within acceptable limits. And as for the FA31s with wobbling elements again pentax QC was slack there especially considering the cost of that lens.

---

Last edited by Digitalis; 07-30-2014 at 03:54 AM.

[Class A]

More glass in a lens leads to typically worse flare tolerance, and also increases optical complexity to counter additional problems caused by the addition of extra lens elements.

A "cost-cutting" design (as you put it earlier) is one that uses as few as possible lens elements.

In lens design, a high number of lens elements suggests high performance (more correction) and implies higher manufacturing costs.

More lens elements need not cause worse flare tolerance, apparently:

It is interesting to see that lens tests have made it apparent that the sigma 18-35mm f/1.8 lens has better resolution and contrast across the frame @ 30mm compared to either versions of the sigma 30mm f/1.4.

The Sigma 18-35/1.8 has 17 lens elements in 12 groups and according to your statement flares less than the 7 lens elements in 7 groups version of the Sigma 30/1.4.

Hence suspecting that the 9 lens elements in 8 groups version of the Sigma 30/1.4 may flare more than the older version does not appear to be warranted.

The newer design is using more glass to compensate for optical errors that could be effectively countered by using a single ED, UD or Aspherical lens element.

The MTF charts show that the optical design counters aberration sources better than the old version. It seems to me that unless weight is the primary concern, it should not matter whether better performance is achieved through using more lens elements or exotic (more expensive) lens elements.

I have never explicitly said Sigma lens coatins are bad...

You chose other words:

"we all know sigma's lens coatings leave a lot to be desired"

"Sigma coatings aren't that great"

" the flare resistance of the sigma 8-16mm f/4.5-5.6 is simply abysmal." (in other posts you link flare resistance with coatings and I have never seen any other person call the Sigma 8-16mm's flare resistance abysmal.)

"...though of course lens coating have a significant effect on [flare], I wouldn't hold my breath on whether Sigma has made any improvements in this area. In my experience sigma lenses flare really badly - though there are always exceptions."

Sigma coatings may not be as exceptional as Leica coatings for instance and it is fair enough if your share your opinion, but if someone with little experience and not knowing your background/benchmarks (e.g., someone like Mirton) reads your opinion about Sigma coatings, they will think that one should better avoid Sigma lenses.

I think that they would take away the wrong conclusions.

If I see a scientific comparison that demonstrates that standard Pentax coatings are worse than Sigma coatings, I will not oppose to Sigma coatings being characterised as subpar. That demonstration has not been made, though, and I would have counterexamples already.

I have experienced a number of issues that have arisen with new lenses from Canon and Nikon. I don't think it is relevant to discuss them on a Pentax camera forum,

I agree, but either you don't have many Pentax lenses or you have been very lucky with them. I don't think anyone can authoritatively state that Sigma QC is worse than Pentax QC so I don't like it when people use opportunities to bash Sigma while sparing Pentax.

I admit I have made my annoyance apparent at sigma more than once, but only to give a fair warning for people to be vigilant for faults when buying lenses.

I support fair warnings, but as I said, I'm concerned that if they are issued in an unbalanced way, they will have the effect of recommending one brand over the other even though there is no hard evidence to support generalised statements or repeated criticism towards one brand only.

I'm unaware of how this lens handles in difficult lighting in regards to AF lock behavior but considering my experience with Pentax DA, and FA lenses on my Pentax K5IIs I would think the AF would have greater reliability and accuracy than what I have experienced with sigma lenses.

The camera body is responsible for determining focus expediently and with accuracy.

The optical performance of a lens can have an impact on AF performance, e.g., spherical aberrations lead to "focus shift", but the latter phenomenon is taken care of by appropriate AF information in the lens' flash memory (read out by the camera for AF purposes), and only pretty poor lenses with low contrast or heavy aberrations should actually affect AF performance. A standard AF field "sees" with with an effective aperture of f/5.6 so lenses don't even need fantastic wide open performance.

Again, if anyone can scientifically demonstrate that one manufacturer consistently produces lenses with worse AF results then I won't object to such statements anymore.

That is rather slippery statement the Pentax DA*16-50mm f/2.8 ED AL [IF] SDM is actually a Tamron lens - so who is really to blame for the de-centering issues?

Are you thinking about the Tamron 18-250/3.5-6.3?

That was a Tamron lens that Pentax rebadged. The 16-50/2.8 was co-developed with Tokina. It does not really matter, though who the designer/manufacturer is. If Pentax sells it, their QC must make sure that customers don't receive an undue amount of decentered copies (that will additionally typically suffer SDM-death, repeatedly).

The DA*55mm f/1.4 mis-focusing on a K7 I don't really consider to be all that problamatic, the K7 has the capability to adjust AF for individual lenses.

Robgo2 had different issues. Follow the thread, if you are interested. BTW, his experience rhymed with DPReview's report who reported that they went through three copies of the DA* 55/1.4 and none of them was optically OK. For testing they chose the one with the least defects, but what a poor performance by Pentax (or the dealer) was that?

And as for the FA31s with wobbling elements again pentax QC was slack there especially considering the cost of that lens.

I fully agree.

At the price point of an FA 31/1.8, optical issues should be the rare exception. Sadly, they don't seem to be (the many not so hot copies giving rise to the "MIJ better than AIV" myth).

Sigma lenses are not nearly as expensive, but yet you seem to expect better QC from Sigma than you do from Pentax.

I respect your experience and enjoyed a number of your postings and only wish your Sigma comments would not come across as if you were someone who had an axe to grind with Sigma.

[Mirton]

=Class A;2892103Lenses do not contain AF algorithms.

The camera body is responsible for determining the best focus setting.

Lenses do still have an influence on AF through various factors, one of them being the AF adjustment tables stored in the flash memory of a modern lens. If this table is not matched to the tolerance of a particular camera body, it will lead to focus errors and will have to be updated (to work with this particular camera body).

[Original post] I've read that Sigma doesn't licence the AF algorithms from the other manufactures but reverse-engineers them, which might explain why there's so many AF issues with their lineup.

I never stated that lenses contain algorithms, I said that Sigma doesn't licence the [ in-camera body] algorithms directly from Pentax (NIkon, Canon or Sony), but reverse engineers them, that's is reproduces such algorithms by extrapolating them in their own labs. I personally don't feel neither a Sigma hater or a fanboy in that regard but a objective reviewer ( like many here in the forum). I own quite a lot of Sigma glass, from the humble Super Wide II AF 24mm to the expensive Sigma EX Dg 300mm f2.8 and the new Art 18-35mm f1.8. I try share my experience with these lenses without prejudice or agenda, to better inform my fellow pentaxians.

In response to the Sigma USB Dock, I think its more of a gimmick than a useful tool, Sigma is basically outsourcing its troubleshooting to its customers. There's no need for me or anyone else to tweak and calibrate a lenses auto-focus, It should work well from the get-go. There's a reason why no other manufacturer provides such an "option", because It's tedious and unnecessary (unless you're an engineer or retiree and enjoy these kind of things) The "genius" of Sigma relies on the fact they have re-branded it as an accessory and are making its customers foot the cost of production by charging us $60-80 for it instead of making it a neccessary part of the Art-series lens kit as they should.

I personally stopped fretting about sharpness and corner performance, CA, etc. If I were concerned about purple fringing, etc. I would have to reject a lot of Pentax lenses, including Limited lenses. However, I now look at the big picture and ask myself whether the images produced by the lens evoke a kind of feeling that I like. The actual difference in the evoked feeling between two lenses can be small and subtle and you won't find it pixel peeping at a 100% magnification, but AFAIC at a subconscious level it is quite real and significant.

That's why I spend quite a bit of money on a FA 31/.1.8 (making sure it is not one of the many copies with loose internal lens groups).

I personally feel that the Sigma's coating delivers in CA and PF control but lacks in 'CHARACTER'. I compared subjectively my newer Sigma Ex dg 85mm f1.4 to my older Pentax-F 50mm f1.4, the 50mm in my eyes delivered better contrast, better colors than the sigma. The new 18-35mm f1.8 "Art" seems to have improved coating over the older Sigma line, It's not DA* rendering, and Liking it might be a strong word, let's just say i'm getting used to it gradually. ( I'd still chose my Rokinion 35mm f1.4 UMC's coating over the Sigma's any day of the week, a company that doesn't have Sigma's pedigree, but has made me a big fan of the UMC)

Note: The Rokinion/Samyang 35mm f1.4 may also exhibit quality control issues, my copy has problems with the aperture control mechanism, but when it works in terms of IQ its a stellar performer.

[Nicolas06]

The camera body is responsible for determining focus expediently and with accuracy.

The optical performance of a lens can have an impact on AF performance, e.g., spherical aberrations lead to "focus shift", but the latter phenomenon is taken care of by appropriate AF information in the lens' flash memory (read out by the camera for AF purposes), and only pretty poor lenses with low contrast or heavy aberrations should actually affect AF performance. A standard AF field "sees" with with an effective aperture of f/5.6 so lenses don't even need fantastic wide open performance.

Again, if anyone can scientifically demonstrate that one manufacturer consistently produces lenses with worse AF results then I won't object to such statements anymore.

A few remarks on AF:

- max apperture of a lens does count in particular high end body tend to have AF sensor also optimized for f/2.8 or f/8 on top of the classica f/5.6... The idea is that when adding a teleconverter, f/8 sensor might be really usefull while f/2.8 sensors are more precise with fast apperture lens (as fast as f/2.8 or faster). And on the contrary a slow lens cannot benefit of f/2.8 sensor. That why f/5.6 is the most common sensor apperture used for AF and most lens avoid to be really slower than f/5.6...
- the body has to send a precise order to the lens for AF, either electronically or just using the body motor that's true. But depending of the lens mechanics the lens will focus slowly or fast, be precise or loose. This is even by design: a slow wide angle has no need for precise AF and can be very fast and innacurate as it is not important. On the contrary a macro lens tend to have very precise focussing that make slower than other designs.
- Lens are typically sensitive to back/front focus. Some lens are more sensitive to it than others. This basically mean that when the body ask the lens to focus at some distance, the lens do not obey the order exactly but tend to move too much or not enough. It is even more problematic on zooms where it can happen that the setting have to be adjusted by focal lens. Some lens design are really known to have this problem with other do not as much.
- Advenced lens design from Nikon (as an example) include a "feedback" system where the body and lens together can check if the mechanics really moved to the right place and to correct if not the case. They tested that on LensRental and found that at least for Nikon system to get the best AF result you needed both a modern high end body AND a modern high end lens. Having only one of the 2 is not enough.
- Lenses with AF and without AF do not have always the same design. Some optical design do not work with AF and one need to compromize the optical design to support AF. That why some famous lens builder keep just making manual lenses. To not compromize the optical design for AF.

All in all... AF is not just a camera body affair.

---------- Post added 07-30-14 at 02:00 PM ----------

Sigma coatings may not be as exceptional as Leica coatings for instance and it is fair enough if your share your opinion, but if someone with little experience and not knowing your background/benchmarks (e.g., someone like Mirton) reads your opinion about Sigma coatings, they will think that one should better avoid Sigma lenses.

Sigma tend to favor design for optimal sharpness in charts and putting less priority on flare control. Ultimately, this is compromize, the faster the lens and the more corrected it is, the more optical elements it tend to have, the worse it tend to work toward flare.

This typicall mean that the 18-35 f/1.8 is insanely sharp even wide open... But is not good performer against flare. As most sigma lenses are zooms or wide apperture prime optimized for sharpness, they tend to not fare very well against flare. On the opposite, Pentax has a few very good lens against flare like DA15, DA21, DA35 (both ltd & plastic wonder) and a few others.

[Pål Jensen]

A "cost-cutting" design (as you put it earlier) is one that uses as few as possible lens elements.

In lens design, a high number of lens elements suggests high performance (more correction) and implies higher manufacturing costs.

"Normal" optical glass is dirt cheap. Having many lens elements doesn't neccesarily cost a lot. Look at all the consumer zooms; particularly "super" zooms.
High quality optical glass may be very expensive. Use of such glass may make for a simpler construction due to less need for correcting elements.
The motivation of buying Sigma lenses is mostly price.

[Digitalis]

either you don't have many Pentax lenses or you have been very lucky with them. I don't think anyone can authoritatively state that Sigma QC is worse than Pentax QC so I don't like it when people use opportunities to bash Sigma while sparing Pentax.

I will admit that before to the year 2004 I never had to buy any pentax lenses. My family already had pretty much everything a photographer would want, it is only in the past few years with the introduction for the FA limited, and DA limited lenses that have piqued my interest enough to buy them. I must have been lucky (Within the scope of APS-C and 35mm lenses) my First Pentax DSLR the K10D I did come with a DA 16-45mm f/4 ED ASPH that was de-centered - but this was replaced with an excellent copy. My FA31 doesn't wobble, and is optically superb. My FA77 did fall apart, but was repaired free of charge and is optically superb, the 43mm f/1.9 Special I have in Leica thread mount is stellar (especially on the Leica monochrom), the DA 15mm f/4 ED ASPH was great with no faults as well. So that is two f*ck ups out of five from Pentax over the years. With the 14 new Sigma lenses I have bought over the past 10 years I can say I have not been so lucky.

only pretty poor lenses with low contrast or heavy aberrations should actually affect AF performance.

In many cases where I have experienced serious focus hunting with my EX Sigma lenses, poor flare handling directly contributed to issues with AF. I'm well aware how phase detect AF systems operate and if a lens doesn't handle flare well there won't be any contrast for the AF system to lock onto. Pentax has made a name for themselves with SMC coatings, and there isn't really anything else other than Fuji EBC coatings that (allegedly) hold any distinct advantage over offerings from pentax*.

" the flare resistance of the sigma 8-16mm f/4.5-5.6 is simply abysmal." (in other posts you link flare resistance with coatings and I have never seen any other person call the Sigma 8-16mm's flare resistance abysmal.)

Compared to the Pentax DA12-24mm f/4 ED ASPH I have recently the pleasure to use in addition to my experiences with the DA15mm f/4 ASPH - so with those excellent lenses in mind I say it again: The Sigma 8-16mm f/4.5-5.6 flare resistance is abysmal. Basically, you have to stop it down to f/11 to gain any control over flare, contrast this with the two super-wide pentax DA lenses which you can use at any damn aperture you want and they will be fine, hell you can even put filters on them without issue. Putting a filter on the Sigma 8-16mm causes a complete blackout in the corners of the image at 16mm. I suppose they put a filter thread on the lens cap as a joke.

Robgo2 had different issues. Follow the thread, if you are interested. BTW, his experience rhymed with DPReview's report who reported that they went through three copies of the DA* 55/1.4 and none of them was optically OK. For testing they chose the one with the least defects, but what a poor performance by Pentax (or the dealer) was that?

I do recall reading about Dpreview having issues with this lens, I assumed it was teething issues as the DA*55mm f/1.4 was relatively new lens at the time.


* I have never tested this, but next time I work with a Hasselblad H and Pentax 645Z in the studio I'll have to.

[normhead]

I admit I have made my annoyance apparent at sigma more than once, but only to give a fair warning for people to be vigilant for faults when buying lenses.

I do the same thing with the Tamron 70-200, if you read the reviews, fully 10% of them come defective... you'd be crazy to buy one and not put it through it's paces during the period that you can take it back without cost... it's apparently a great lens, those who get good ones love them. For people like me who depend on the mail and UPS to move items back and forth. it's a scary lens. You have to accept that you won't have use of your money for weeks while you sort out the return sequence if you get a bad copy. My Sigma 120-400 taught me that. I got two bad copies, in a process that lasted over month, and eventually applied the money towards a DA*60-250. If there is one thing that needs to be emphasized over and over, it's that stuff doesn't always arrive in good working order, whoever you buy from. But based on my experience, you're more at rick with Tamron and Sigma than other manufacturers, with the caveat that my Sigma 70 macro, and Sigma 8-16 are both my favourites in their focal length and don't seem to have a high incidence of DOA reports, so maybe it's better to focus on particular lenses than on the whole company.

---------- Post added 07-30-14 at 08:42 AM ----------

Putting a filter on the Sigma 8-16mm causes a complete blackout in the corners of the image at 16mm. I suppose they put a filter thread on the lens cap as a joke.

The lens hood also has to be removed from the camera with the lens cap. Also a joke...for my use, the lens hood should have just been welded to the lans cap, it would have made my life easier. But I still love the lens...

Flare? What flare?

[Class A]

I never stated that lenses contain algorithms, I said that Sigma doesn't licence the [ in-camera body] algorithms directly from Pentax (NIkon, Canon or Sony), but reverse engineers them, that's is reproduces such algorithms by extrapolating them in their own labs.

Why would Sigma reverse engineer AF algorithms?

All they need to do is to reverse engineer the communication protocol between the lens and the camera. This includes knowing what kind of data is stored in the lens.

Provided they have that, they can use the original bodies (say a Pentax DSLR) and mount their prototype and see how it performs. There is no need at all, to know what the AF algorithm does precisely.

All my Sigma lenses focus as quickly and precisely as my Pentax lenses. There is nothing at all to suggest that Sigma's reverse engineering efforts have not been 100% successful.

In response to the Sigma USB Dock, I think its more of a gimmick than a useful tool,

That's your prerogative.

Fact is that consumer lenses and consumer cameras have tolerances and if by chance a match is made where the combined tolerances exceed the overall maximum tolerance, some adjustment has to take place.

I spoke to a technician in a lens service centre and he said that often it is the customer's camera that is out of whack instead of the lens. That's why a proper centre will ask you to send in your camera as well as your lens because AF adjustment is about creating a pair that works together, and that's not always a matter of fixing a defective lens.

Sigma is basically outsourcing its troubleshooting to its customers.

That is a completely unfounded claim.

In order to support that, you'd have to demonstrate that Sigma has reduced their own QC because they are relying on customers to fix issues.

The latter would not make any business sense at all, because not every customer can be expected to buy the dock. Sigma would hence be facing a lot of lens returns.

There's no need for me or anyone else to tweak and calibrate a lenses auto-focus, It should work well from the get-go.

Tell that to anyone who tried to use one measly AF adjustment value to calibrate a zoom at different focal lengths and different focus distances.

It does not work.

Your only chance to get a zoom properly adjusted to your camera is to find a service centre that actually goes through the trouble of adjusting all AF parameters at multiple focal lengths and focus distances. Good luck with that. The usual response one gets from a service centre is "Lens is within manufacturing tolerances". I'm not saying there aren't exceptions, but I'd rather do the calibration myself than to rely on a technician who thinks that +/- 2% is OK.

There's a reason why no other manufacturer provides such an "option", because It's tedious and unnecessary

Why do Canon and Nikon build AF fine adjustment into their camera bodies then?

Are they not admitting, by offering this feature, that there is a need to fine match equipment?

And remember, one AF adjustment value for a zoom lens is never enough, it is not even enough for a prime. The latter should ideally be calibrated at different focal distances and different aperture values.

If you have the money, Leica may build the equipment that is without issues straight away. But even with high-end Canon and Nikon gear, some calibration will always be necessary for optimal results.

The "genius" of Sigma relies on the fact they have re-branded it as an accessory and are making its customers foot the cost of production by charging us $60-80 for it instead of making it a neccessary part of the Art-series lens kit as they should.

Was it not your position that it is an unnecessary gadget?

Again, you'd have to demonstrate that Sigma purposefully neglects QC in order to make you buy their dock. As I said, this would not make any sense at all from a business perspective as many customers would not bother with the dock and just demand a refund.

[Digitalis]

the lens hood should have just been welded to the lens cap

I agree.