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08-26-2015, 06:42 PM   #166
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QuoteOriginally posted by Class A Quote
Despite making his claims with great conviction, Digitalis has no actual way of knowing how hard or easy it is to get a good copy of the lens. Note that he kept the lens despite having all the money in the world to go for the very best equipment only. Go figure.
Going for an ad hominem are we? I'm not making claims - I'm stating facts. For your information: I have tried several copies before and since purchasing my own, and none of the 18-35mm f/1.8 art lenses, despite using different camera bodies was completely accurate in PDAF Mode. The copy I presently own is by far the most accurate I could find - mainly due to the exhaustive calibrations I have done to it and even then overall AF accuracy is at 78%

The reason why I keep my copy is that it would be unethical to sell it to someone else, I can't return it because of the optical alignment that had to be done to it - and even then, it still doesn't AF accurately.

QuoteOriginally posted by Class A Quote
Why don't you get a copy and see for yourself?
Make sure you buy it from a reputable seller with a good returns policy. Buy from a brick and mortar store if you have to.


Last edited by Digitalis; 08-26-2015 at 06:51 PM.
08-26-2015, 08:17 PM   #167
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i recieved my copy of the 18-35 on monday, ive been playing around with it a fair bit at F1.8 for novelty reasons when realistically I shoot at nothing but F8.0 for the type of stuff I take photos of.

At F8.0 it appears to have no drama's nailing autofocus every time (obviously more real world testing is required). Last night I was messing around taking hand held photos of my sisters dog at F1.8 in poor light conditions, only getting a 50% keeper rate but that was going to be a combo of hand shake and the lens not nailing focus.

I just finished testing the lens on an autofocus test chart, achieving what appears to be about a 7/10 keeper rate.

For me I think the lens is good enough how it currently functions without the need to send it back to C R Kennedy. Very rarely needing to shoot wide open, but when I do I'll keep in the back of my mind to flick the camera over to live view to grab that F1.8 shot.
08-26-2015, 10:53 PM   #168
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QuoteOriginally posted by Digitalis Quote
I'm not making claims - I'm stating facts.
If you do not already know that one cannot make the generalisations that you are presenting as "facts" on the basis of a few personal observations then I will not be able to educate you otherwise.

QuoteOriginally posted by Digitalis Quote
The reason why I keep my copy is that it would be unethical to sell it to someone else, I can't return it because of the optical alignment that had to be done to it - and even then, it still doesn't AF accurately.
Ah, look, that's simple.

Sell the lens for a very ethical $100, exposing every weakness that you know of. That would solve the problem wouldn't it?

According to you we are talking about a dog of a lens, wich is 100% inconsistent to what expert reviewers say, but 100% consistent with your other derogatory comments about Sigma lenses. Luckily the quality of many excellent Sigma lenses can speak for itself.
08-27-2015, 12:26 AM   #169
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QuoteOriginally posted by Class A Quote
If you do not already know that one cannot make the generalisations that you are presenting as "facts" on the basis of a few personal observations then I will not be able to educate you otherwise.
I have considerable field experience with this lens, as well as correspondence with a number of photographers who have owned this lens in various camera mounts. I don't find it surprising that most most of them have sold this lens, largely due to the frustrations of getting the AF to work as well as their brand name* lenses do.

QuoteOriginally posted by Class A Quote
According to you we are talking about a dog of a lens, wich(sic) is 100% inconsistent to what expert reviewers say
I never said the Sigma 18-35mm f/1.8 Is a dog - Those are your words. Optically it is very good, with some faults, notably in OOF rendering which is only to be expected from such an ambitiously designed fast zoom lens. In terms of resolution it offers performance rivaling that of the best primes. However crippling deficiencies in AF accuracy and reliability - not only with Pentax AF systems - prohibit me from recommending it to everyone without a fair warning about its shortcomings.

QuoteOriginally posted by Class A Quote
but 100% consistent with your other derogatory comments about Sigma lenses. Luckily the quality of many excellent Sigma lenses can speak for itself.
I own quite a few Sigma lenses, many of them see continued use due to their reliability and their suitability for my purposes. None of them were given to me, therefore I reserve the right to be openly critical about optical,ergonomic and mechanical shortcomings. If you have a problem with this, and continue to take issue with it...... then allow me to convey the sentiments of my raised middle finger.

QuoteOriginally posted by Class A Quote
Sell the lens for a very ethical $100, exposing every weakness that you know of. That would solve the problem wouldn't it?
Is that an offer? Bear in mind I have to recoup my expenses on this lens.

*and even other sigma lenses in the same focal length range AF with superior accuracy and reliability than the 18-35mm f/1.8 ART, which is a telling revelation.


Last edited by Digitalis; 08-27-2015 at 12:56 AM.
08-27-2015, 12:40 AM   #170
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QuoteOriginally posted by Class A Quote
100% inconsistent to what expert reviewers say
Not all expert reviewers, or even all expert users, have found the AF to be consistent in the 18-35. On Pentax, Canon and Nikon, for example.

It may be necessary to accept that some of the recent Sigma Art series lenses have trouble with AF. It's not unheard of - both Tamron and Sigma, for example, have issued several lens firmware updates over the last few years to fix various bugs and improve lens performance for several of their new lenses. Including for the 18-35 (eg on Canon)
08-27-2015, 12:46 AM   #171
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QuoteOriginally posted by Digitalis Quote
Buying a good copy is the ticket - but the chances of that are certainly against you. Testing the lens is rather difficult, there are still optical centering issues present with the ART series lenses despite sigma saying otherwise. The lens dock is the closest thing to a solution as you will ever get, and even then it is a band aid at best.



The lens dock will set you back about $100, a high quality polariser will also cost an extra $200.A proper lens calibration target will set you back about $80

If you do choose to get it, spend some time getting to know its quirks, and the situations where it is likely to be less than accurate. Don't waste your time with in-camera AF corrections, as it is only really designed with primes in mind.

Get the Sigma lens dock, calibrate your lens properly with an accurate target*, and be warned that focusing on anything at a distance between 2m and infinity has at least a 90% of being out of focus at f/1.8 - and the bokeh from this lens is rubbish at that distance, it only delivers smooth results with acceptable consistency at focus distance of 0.5m or shorter @ f/1.8. Remember to stop the lens down, I know you probably want to use this lens at f/1.8 all the time, but the reality is at the f/4 ~ f/11 aperture range you will have a higher keeper rate.



At least the calibration software is free. It can be downloaded from the sigmaphoto website.

Even if you do all of this perfectly, there is still a high chance your lens will never be absolutely reliable or accurate at apertures wider than f/4

To be honest: if you are buying this lens hoping it will perform perfectly out-of-the-box to document a once-off** event like a wedding this, this particular lens isn't worth the trouble, It is simply too unreliable.


*Brick walls don't cut it. You need a high contrast, target for accurate repeatable calibration at f/1.8.
**hopefully, with divorce rates being what they are..and all that Ashley Madison controversy going on.
I sign under everything written. For this price I expected less problems with this lens.
I have a USB dock and I really made an effort to adjust it according to the instructions(for K-3). Frankly, it annoyed me so much that it almost became a flying lens.
But there is no surrender In the future I will definitely strongly consider before buying Sigma lens.
Has anyone done customization over USB dock on this lens and managed to bring lens in a "usable" condition? Is it possible that we share this results and make some kind of comparison?
Do not get me wrong when the lens focuses accurate results are excellent. The problem is that lens betrays you when it really matters

Thanks in advance

P.S.

English is not my native language so sometimes I sound like Tarzan






08-27-2015, 04:57 AM   #172
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I know three things about this lens:

1) The staff review here praised its optical performance to the high heavens while panning its AF performance on anything but live view. It is in the nature of DSLR photography to shoot through the eyepiece, or we'd all go mirrorless. If shooting in live view is the only way the staff review could get the AF to work correctly, that's a significant handicap.

2) Yes, there are workarounds, but they shouldn't be necessary. Remember that the Pentax AF system has to cope with two AF lenses in current production that are f/1.4 (the FA 50 and the DA*55) and one that is f/1.8 (the DA50/1.8), so for an f/1.8 lens to give it trouble tells me that it isn't just about the wide aperture.

3) After reading said staff review, there was no way that I was going to take a chance on this lens when I live 400+ km from a bricks and mortar store and can only receive or return the lens through the post - which potentially offers some unscrupulous person the ability to claim that it was transport damage rather than a lens fault in the event that I should try to return a bad copy. (I should note that the store I would actually use seems quite reputable, but other vendors are not necessarily the same.)

Frankly, I'm more inclined to side with Digitalis's ongoing bad experience with this lens and his colleagues' bad experience on multiple platforms than Class A's unremitting defence of the lens which appears to be based on being lucky enough to get a good copy first off that nails it every time.

QuoteOriginally posted by Class A Quote
Luckily the quality of many excellent Sigma lenses can speak for itself.
That depends on
, I guess.

(NSFW for language)
08-27-2015, 06:51 AM   #173
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^ that guy is just being negative and spiteful about sigma ART lenses in general. His comments about ED glass are based on the myth that it degrades image quality: ED glass it doesn't eliminate chromatic aberration, it merely reduces it, by reducing the spectral dispersion of light that is caused by traditional borosilicate glass. The Nikkor 200mm f/2G ED VR is STUFFED with ED glass* and it is a stunning lens to work with. His comments that ED glass is a bad thing are nothing more than uninformed stupidity...UGH


* 3 high grade ED lenses, plus one extra high grade ED element.

08-27-2015, 07:43 AM   #174
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His philosophy and beliefs on optics are interesting to say the least.
08-27-2015, 07:58 AM - 1 Like   #175
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I am continually astonished that the people who have "good copies" don't send a copy to PF and demand a new evaluation. I posted a long time ago in the thread that the way to shut people up on this topic would be to showcase in a rigorous test how well this lens worked along side other fast aperture lenses of similar quality. Personally this lens was high on my buy list until the PF review and then it fell away and never came back into my vision.
08-27-2015, 08:48 AM   #176
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QuoteOriginally posted by UncleVanya Quote
I am continually astonished that the people who have "good copies" don't send a copy to PF and demand a new evaluation.
You're right, you know. Of course this doesn't erase the initial bad experience, especially since the PF staff went to the trouble of obtaining multiple copies and then were so shocked by what happened that they went back and obtained MORE after initial testing, and found the same issue with just about all of them. They were desperate to give this lens a good reputation, and they went far beyond what they've done with just about every other test in order to do so. That doesn't deny the incredible good luck of the people who obtained perfect working copies that have never had a problem, but it still leaves a great big shadow hanging over it and the obligation to warn anybody who buys one about what they might be getting into.
09-25-2015, 09:37 AM   #177
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I'm starting to see what Sigma was talking about. The ability of the K-5IIs to focus below f/2.8 is garbage. I get just as many misses with the FA31 and FA77 as I do with anything. If I'm in bright light, it's usually ok, but in modest light or without flash to help focus, it's 50% at best. Probably lower.
09-25-2015, 12:09 PM   #178
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QuoteOriginally posted by Digitalis Quote
crippling deficiencies in AF accuracy and reliability
At the end of the day, I have a two part question for you:

1) What f/1.4 and f/1.8 autofocus lenses do you own, aside from this dreaded Sigma?
2) Do you have any problems nailing focus with these on the camera(s) you've used the 18-35 Art on?
09-25-2015, 08:30 PM   #179
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QuoteOriginally posted by pathdoc Quote
1) What f/1.4 and f/1.8 autofocus lenses do you own, aside from this dreaded Sigma?
well, since you asked....

Pentax F 50mm f/1.7
Pentax F 50mm f/1.4
Pentax FA 50mm f/1.7
Pentax FA 50mm f/1.4
Pentax FA 31mm f/1.8 Limited
Pentax FA 77mm f/1.8 Limited
Pentax FA*85mm f/1.4
Sigma 24mm f/1.4 ART (Nikon F mount)
Sigma 35mm f/1.4 ART (Nikon F mount)
Sigma 50mm f/1.4 EX (Canon EF mount)
Sigma 50mm f/1.4 ART (Nikon F mount)
Sigma 85mm f/1.4 EX (Canon EF mount)
Canon EF 24mm f/1.4L
Canon EF 35mm f/1.4L
Canon EF 50mm f/1.0L
Canon EF 50mm f/1.2L
Canon EF 50mm f/1.4
Canon EF 50mm f/1.8
Canon EF 50mm f/1.8 II
Canon EF 85mm f/1.2L II
Canon EF 200mm f/1.8L
Nikkor AF-S 24mm f/1.4G
Nikkor AF 28mm f/1.4D
Nikkor AF-S 35mm f/1.4G
Nikkor AF 50mm f/1.4D
Nikkor AF-S 50mm f/1.4G
Nikkor AF 50mm f/1.8D
Nikkor AF-S 50mm f/1.8G
Nikkor AF-S 58mm f/1.4G (special)
Nikkor AF 85mm f/1.4D
Nikkor AF-S 85mm f/1.4G



QuoteOriginally posted by pathdoc Quote
2) Do you have any problems nailing focus with these on the camera(s) you've used the 18-35 Art on?
I still have issues with AF accuracy with this lens on my K5II Pentax K10D and loaned K3II bodies. Even with stringent AF calibration with the Lens dock*. My colleagues and students who also regularly use f/1.2~f/1.8 primes also have difficulties with AF accuracy with this particular lens on various Canon and Nikon camera bodies**. While AF inconsistencies are well known trade-off with faster lenses due to their inherently low contrast, which PDAF requires to be able to see the phase differential. The 18-35mm f/1.8 - with its high contrast even at f/1.8, still manages to be by far the least accurate with PDAF even when compared to older AF lenses (like the Nikkor D series)

* In-camera AF calibrations with this lens are completely pointless.
** I don't know anyone who uses this lens on sigma cameras - sigma photographers generally seem to be rather quiet bunch. The AF module on Sigma cameras is similar to the K10D.

Last edited by Digitalis; 09-25-2015 at 08:50 PM.
09-26-2015, 10:38 PM   #180
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QuoteOriginally posted by Digitalis Quote
While AF inconsistencies are well known trade-off with faster lenses due to their inherently low contrast, which PDAF requires to be able to see the phase differential.
Is this still the case for the FA31? I find its contrast to be quite excellent, certainly better than several other lenses I own. The FA50 f/1.7 has far worse contrast yet it seems to focus much better for me. The FA77, however, often displays poorer contrast than the FA31, especially in bright light, probably because I use the built-in hood, which is likely not sufficient.
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