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05-26-2016, 02:03 AM   #211
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QuoteOriginally posted by Sandy Hancock Quote
My DFA15-30 arrived today
That was fast!...I hope you have better luck finding a centered copy, I'm already on my third copy of this lens.

05-26-2016, 02:22 AM   #212
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QuoteOriginally posted by Digitalis Quote
That was fast!...I hope you have better luck finding a centered copy, I'm already on my third copy of this lens.
Digitalis, I'm planning to get this lens also... but I'm a terrible lens tester. Can you explain in a few words how to test this lens for de-centering?
05-26-2016, 02:47 AM   #213
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QuoteOriginally posted by Hattifnatt Quote
Can you explain in a few words how to test this lens for de-centering?
A quick and dirty way of testing for it is to use a subject at infinity focus, ensure the camera is level: take one shot, then flip the camera upside down, level it: and take another shot. If there is any difference in resolution or contrast appearing in opposing sides of the images your lens may be defective. Without using a testing bench de-centering can be difficult to detect as there is more than one direction a lens can be misaligned. But unfortunately because I have a testing bench, I feel oddly compelled to test my lenses...and on a bench the slightest defect in centering can be detected in a matter of seconds.
05-26-2016, 09:48 AM   #214
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Anyone with intimate Sigma knowledge around? What happened to the 12-24 lens? Why's it out of production?

05-26-2016, 11:41 AM   #215
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QuoteOriginally posted by funktionsfrei Quote
Anyone with intimate Sigma knowledge around? What happened to the 12-24 lens? Why's it out of production?
I thought I read they designing a ART version.


I owned a HSM II version, sold it at half price after using for 8 months, It was wide, but not really sharp in terms of micro contrast. I have yet to get a shot where I would be really happy with it. I replaced it with a Rokinon 14mm which has amazing micro-contrast and sharpness. However the issue with that is, it has distracting star burst pattern when shooting night lights, and since I do a lot of night city scapes, it was not good in that regard. I finally decided on the DFA 15-30 on a K1 body, and this seems to have good starbursts, sharpness and micro-contrast can be coaxed out of it in post.

Last edited by K-amps; 05-29-2016 at 12:26 AM.
05-26-2016, 11:53 AM   #216
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QuoteOriginally posted by Digitalis Quote
That was fast!...I hope you have better luck finding a centered copy, I'm already on my third copy of this lens.
such expensive lens and yet defective? I don't get this. It's 2016 and companies are still releasing defective lenses to the market. Can't they have some quality measures for that?
05-26-2016, 12:03 PM   #217
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QuoteOriginally posted by Nitrogliserin Quote
such expensive lens and yet defective? I don't get this. It's 2016 and companies are still releasing defective lenses to the market. Can't they have some quality measures for that?
Yes a bit frustrating... A friend of mine got the Tammy version for $899, and it has IS/VR. The DFA is without IS/VR and costs $1445. Tammy is known to have decentering issues in the past. Even glue coming off... I am wondering if mine is out.... is not as sharp as my rokinon was on a 22mp body
05-26-2016, 12:48 PM   #218
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QuoteOriginally posted by Nitrogliserin Quote
such expensive lens and yet defective? I don't get this. It's 2016 and companies are still releasing defective lenses to the market. Can't they have some quality measures for that?
Nuh, it's the way of the world.

The owner of Lens Rentals gets to sample enough lenses that his tests become statistically significant, and he finds the same variation patterns in all glass, even Canon L Series.

Always be prepared to test a lens when you buy it, whatever its brand - and to keep sending it back until you get a decent copy.



05-26-2016, 01:01 PM   #219
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QuoteOriginally posted by Nitrogliserin Quote
such expensive lens and yet defective? I don't get this. It's 2016 and companies are still releasing defective lenses to the market. Can't they have some quality measures for that?
To be fair, this is a FF ultrawide and really fast lens. This is basically worst case scenario for decentering potential. And Digitalis has a bench and is a little obsessive with fairly high standards. The copies he returned might have been good enough for average users (would like to see him elaborate about how bad the decentering was. how noticeable it would be in everyday use at f8-f16)

Another method for decentering is to take shots near the minimum focus distance and wide open, of some subject that covers the whole DoF area, like a newspaper layed out at 45 degrees to sensor. Now compare the different sides of the image - are some corners oddly blurry? is the DoF diagonal? Is the CA different in different sides of the lens? Keep in mind that even on a normal lens, the DoF can be curved. What you are looking for is drastic changes in quality in different parts of the image. In worst cases, a whole half of the photo will be completely unsharp/blurred.
05-26-2016, 03:56 PM - 1 Like   #220
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QuoteOriginally posted by Na Horuk Quote
To be fair, this is a FF ultrawide and really fast lens. This is basically worst case scenario for decentering potential. And Digitalis has a bench and is a little obsessive with fairly high standards. The copies he returned might have been good enough for average users (would like to see him elaborate about how bad the decentering was. how noticeable it would be in everyday use at f8-f16)

Another method for decentering is to take shots near the minimum focus distance and wide open, of some subject that covers the whole DoF area, like a newspaper layed out at 45 degrees to sensor. Now compare the different sides of the image - are some corners oddly blurry? is the DoF diagonal? Is the CA different in different sides of the lens? Keep in mind that even on a normal lens, the DoF can be curved. What you are looking for is drastic changes in quality in different parts of the image. In worst cases, a whole half of the photo will be completely unsharp/blurred.
My experience with 24-70L II is that infinity and close focus could have different behavior - and I'm on the 5th sample currently. My Zeiss ZE 25/2 is the third unit (first unit was 30% of the frame being soft on the left side, this 3rd unit is 10% soft (left side too) which is "normal and expected" according to a Zeiss tech support in Germany. I remember that very same guy mocked Japanese lenses QC when giving presentations at Zeiss events). Those lenses didn't pass the infinity test which showed the flaws. The better brands for this kind of issue are Leica M and Sigma Art. With Sigma you could still get a decentered unit but the chance is much lower than Canon and Zeiss ZE/ZF in my experience.

So yeah, it kinda pisses me off the manufacturers sell high-end lenses but think they don't have any obligation to deliver good quality units.
05-26-2016, 04:09 PM   #221
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QuoteOriginally posted by scopedude Quote
So yeah, it kinda pisses me off the manufacturers sell high-end lenses but think they don't have any obligation to deliver good quality units.
That makes me feel good about my very slightly decentered Samyang 14mm. Only replaced it once. Coincidentally, its an FF lens, and probably one of the most affordable UWA primes
05-26-2016, 04:14 PM   #222
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QuoteOriginally posted by scopedude Quote
it kinda pisses me off the manufacturers sell high-end lenses but think they don't have any obligation to deliver good quality units.
Not being a lens expert it really confuses me how all these decentered lens get out the door. if it is so easy to detect in teh field, a simple test on a tripod surely the same thing would be easy to test for in the factory? Easier since they would presumablly have some sort of test bench to put it on. So 30 seconds to put the lens on a machine and test it?

Seems like I am missing something.
05-26-2016, 04:42 PM   #223
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My situation with the 24-70L II was made even more difficult because this lens (good copy) exhibits a curvature at infinity past 24mm. So landscape photos with subjects far away will only be sharp in the center (30-40% of total frame) and gets mushy to the edges. This is very evident around 35mm-50mm settings and no f/8 or f/11 would help. When I brought this over to some photogs in another forum they confirmed this (and mostly just realized). I'm selling this last lens of mine and will never look back

Bottom line is, every lens got its own character, and testing when buying is mandatory. I'm happy to report that my D-FA 28-105 is well centered and gives me sharp infinity focus I could never get with the L lens.
05-26-2016, 04:50 PM   #224
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QuoteOriginally posted by jatrax Quote
Not being a lens expert it really confuses me how all these decentered lens get out the door. if it is so easy to detect in teh field, a simple test on a tripod surely the same thing would be easy to test for in the factory? Easier since they would presumablly have some sort of test bench to put it on. So 30 seconds to put the lens on a machine and test it?

Seems like I am missing something.
I'm a little puzzled, too. But this illness afflicts all manufacturers - perhaps they reckon that a 2% or so return rate is in line with products in other industries, and don't do enough testing of everything that comes off the assembly line.

https://www.lensrentals.com/blog/2010/11/how-to-test-a-lens/
05-26-2016, 04:59 PM   #225
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QuoteOriginally posted by jatrax Quote
if it is so easy to detect
Maybe, but I think it is not so easy to correct it.

They probably can only repeat the assembling process the same way it was done in production, and hope it will improve. If not, another try, and then maybe replace parts.
I guess we are talking of variations of not much more than 1 mikron where the lens elements are sitting.
And in some cases probably also the case may be the culprit.

EDIT:
I know all this can be done in QC during production.
Leica was known to do it (at least in the past), but you payed for it.
And I heard Pentax does this kind of expensive manual checking only with Limiteds.

Last edited by RKKS08; 05-26-2016 at 05:04 PM.
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