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04-10-2016, 10:28 AM   #31
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QuoteOriginally posted by Biro Quote
If you can try out a lens before purchasing or if your photo shop has an excellent return policy, buy one or both and try it out.
Buying online in the European Union means you've got a legal 14 day returns period, plus another 14 days to actually return the goods from the time you informed the seller you'll send it back. I definitely plan to give the lens a detailed but careful test for focusing issues, sharpness and decentering and then decide whether it meets my expectations or not.

It's always kind of difficult to tell whether a lens is as sharp as it can be, because evaluations are always subjective. I may look at the results and think that they are not as sharp as expected, but they may well be all the lens can deliver, or I might just as well have a bad copy. No way to tell. Unless I find some really obvious flaws I will probably have to upload some full-res shots and ask people on here what they think and whether it's the best the lens can do, or whether I should get another copy

04-10-2016, 10:51 AM   #32
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i personally would recommend the 3.5 as its a lens i recently sold. nothing wrong with the lens, but i'm gearing towards the full frame, thus i sold that, and i greatly miss that lens.

one thing i noticed with my other lenses that go up to f5.6 is that i cant really use those lenses indoors effectively for parties/weddings etc that aren't too well lit. a flash or two may help, but you're also adding that to your cost. the constant f3.5 on the other hand is very usable. it maybe big, but the images you get out of it are superb and really sharp.
04-10-2016, 10:52 AM   #33
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I think you have to ask yourself how often will you use 3.5? If you do mostly landscapes the answer would be not too often. Save the $ and go for the slow one. I have it and can't find any reason to get a 3.5

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04-10-2016, 11:12 AM   #34
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QuoteOriginally posted by slip Quote
I think you have to ask yourself how often will you use 3.5? If you do mostly landscapes the answer would be not too often. Save the $ and go for the slow one.
That's the thing, in the UK the f/3.5 is actually cheaper by about 40. I could add a 82mm ND1000 and break even. Considering that, the f/3.5 actually has the edge with its HSM and full time manual focus. The CPL would be much more expensive, but apparently that doesn't work well with UWAs anyway. The size difference would be small, and the f/3.5 would even be lighter than my 17-50 f/2.8.

So it's really just down to image quality, and that seems to be slightly better on the f/3.5 according to the replies in this thread, with a slight edge in sharpness and better flare resistance.

But as somehow has noted before, I am probably splitting hairs.

04-10-2016, 11:21 AM   #35
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On a related note - the use of CPLs with UWA lenses is often discouraged as the effect varies significantly in strength from one edge to the other. But I noticed that all the sample images of and posts about this only ever mention or show the sky. Does the same apply to removing reflections on water, increasing overall contrast etc., or would a CPL still be useful at 10 mm for taking the glare off wet rocks at a waterfall or being able to see through the water in the foreground of a landscape shot?
04-10-2016, 11:53 AM   #36
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I have the Sigma 8-16, which I got with the intent to use for landscapes. I find I use it much more indoors ( which surprised me), where the constant f/3.5 10-20 would work better. I find the lower speed of the 8-16 discourages me from using it sometimes. If I were doing it over, I'd strongly consider the f/3.5 lens for the extra speed, particularly at the long end. The big draw of the 8-16, of course, is the extra 2mm on the wide end. If money were no object, I'd have both the 8-16 and the f/3.5 10-20. Just between the two 10-20s, I would choose the f/3.5 version even if it were significantly more expensive. That extra stop-and-a-half or so makes a huge difference in low light, making it more valuable than a slight IQ advantage.
04-10-2016, 11:57 AM   #37
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ISFA the orientation of polarization depends on the angle at which light hits then bounces from a reflecting surface, the intuitive expectation would be that reduction of glare from shiny objects with a CPL would vary across the frame pretty much regardless of the focal length being used. In practice, however, I'm not certain.
04-10-2016, 12:24 PM   #38
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QuoteOriginally posted by WPRESTO Quote
ISFA the orientation of polarization depends on the angle at which light hits then bounces from a reflecting surface, the intuitive expectation would be that reduction of glare from shiny objects with a CPL would vary across the frame pretty much regardless of the focal length being used. In practice, however, I'm not certain.
I think you're right.

Certainly ultra wide lenses with polarizers either linear or circular show decided variation in sky darkening across the frame. I imagine that this variation occurs with ordinary wide angle lenses and to a smaller extent with normal lenses, but either it doesn't bother us or exposure latitude "covers" it up. And shooting water I'd guess we don't expect the uniformity of effect that we do with the sky.

I've used a CPL with my 10 - 20 (I bought the filter for another format) and had little problem with the sky, although it wasn't prominent in the image.

04-10-2016, 04:28 PM   #39
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QuoteOriginally posted by grhazelton Quote
I think you're right.

Certainly ultra wide lenses with polarizers either linear or circular show decided variation in sky darkening across the frame. I imagine that this variation occurs with ordinary wide angle lenses and to a smaller extent with normal lenses, but either it doesn't bother us or exposure latitude "covers" it up. And shooting water I'd guess we don't expect the uniformity of effect that we do with the sky.

I've used a CPL with my 10 - 20 (I bought the filter for another format) and had little problem with the sky, although it wasn't prominent in the image.
Even normal lenses with a polarizer may show variation in sky darkening, depending on which part of the sky relative to the sun's position is in the picture. Skylight is not uniformly polarized, either in degree or orientation.
04-10-2016, 06:12 PM   #40
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QuoteOriginally posted by FantasticMrFox Quote
Does the same apply to removing reflections on water, increasing overall contrast etc., or would a CPL still be useful at 10 mm for taking the glare off wet rocks at a waterfall or being able to see through the water in the foreground of a landscape shot?

These are all excellent uses, FMF.


The caution is for the sky particularly near the sun. I find you get white, and the other side of the pic is blue.

Last edited by clackers; 04-10-2016 at 06:37 PM.
04-10-2016, 10:34 PM   #41
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Sigma 10-20 f/3.5 vs f/4-5.6

The reason that different reviews don't agree on which lens is sharper, (because the reviews are all over the place with the Sigma 10-20s) is because these lenses do not have the greatest quality control. Some reviewers got a better copy of the f/3.5 while others got a better copy of the f/4-5.6. Good copies of the lenses will have comparable sharpness. Whichever version you decide to get check for off-centering as this is the main cause, especially in wide angle lenses, for lens performance variance.

I eventually decided to purchase the f/4-5.6 because the f/3.5 version has a very prominent yellow cast, (which as far as I know is universal with the f/3.5) I did not want to go through hoops trying to get the color balance of the f/3.5 to where I wanted it to be, so I opted for the f/4-5.6.

In short, quality control is quite erratic on these lenses which is why professional and user reviews are all over the map, the only differences I considered noteworthy when I was deciding between these lenses is the f-stop, the weight/size, (18.3 vs. 16.4 ounces, fairly close to each other), 7 vs. 6 aperture blades, (according to Pentaxforms), and the color balance.

Hope this helps.
04-11-2016, 04:39 AM   #42
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QuoteOriginally posted by SGOMMO7 Quote
The reason that different reviews don't agree on which lens is sharper, (because the reviews are all over the place with the Sigma 10-20s) is because these lenses do not have the greatest quality control. Some reviewers got a better copy of the f/3.5 while others got a better copy of the f/4-5.6. Good copies of the lenses will have comparable sharpness. Whichever version you decide to get check for off-centering as this is the main cause, especially in wide angle lenses, for lens performance variance.

I eventually decided to purchase the f/4-5.6 because the f/3.5 version has a very prominent yellow cast, (which as far as I know is universal with the f/3.5) I did not want to go through hoops trying to get the color balance of the f/3.5 to where I wanted it to be, so I opted for the f/4-5.6.

In short, quality control is quite erratic on these lenses which is why professional and user reviews are all over the map, the only differences I considered noteworthy when I was deciding between these lenses is the f-stop, the weight/size, (18.3 vs. 16.4 ounces, fairly close to each other), 7 vs. 6 aperture blades, (according to Pentaxforms), and the color balance.

Hope this helps.
Thanks for your input. Finally got an answer that makes sense. Did you have to go through many copies of the 10-20 4-5.6 to find a good one ? I assume if you purchased it used you may not have had that luxury to return it over an over again. Mine is a little mushy in the upper left hand corners but very sharp in the middle and elsewhere. So I am keeping it, plus I got a great price.
04-11-2016, 09:55 PM   #43
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QuoteOriginally posted by Driline Quote
Thanks for your input. Finally got an answer that makes sense. Did you have to go through many copies of the 10-20 4-5.6 to find a good one ? I assume if you purchased it used you may not have had that luxury to return it over an over again. Mine is a little mushy in the upper left hand corners but very sharp in the middle and elsewhere. So I am keeping it, plus I got a great price.
I bought new so I would have the option of returning. My first copy of the lens needed returned as it was noticeably decentered.

Yeah, if you going to buy used you just need to ask yourself, "are you feeling lucky?"
04-12-2016, 03:46 AM   #44
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QuoteOriginally posted by FantasticMrFox Quote
A good thread, but it looks like by defishing I would lose a precious 2 mm, and the lens doesn't take filters, which is kind of a deal breaker.



Interesting point I hadn't thought about so far.
QuoteOriginally posted by FantasticMrFox Quote
Interesting point I hadn't thought about so far.
Yes. I forgot to mention the odd starbursts. Instead of single lines, the starbursts have double lines which is not your typical starburst look.
04-12-2016, 09:04 AM   #45
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The Sigma UWA zoom lenses generally have the reputation of variable quality control. Getting those complex lenses just right is difficult, considering the price point especially. In particular, the ratings on the two 10-20s and the 12-24 (full frame) vary hugely due to the sample variation. The 12-24 (original design) can be spectacular - and much better in terms of low CA than the Pentax/Tokina 12-24 (crop only) - if you get a good copy. The testing right here at PF shows that. Then again, some reviews yield low ratings almost certainly due to decentering.

The 8-16 seems to have fewer issues, based on the reviews and customer ratings. As a newer design, that makes sense. Clearly, Sigma has improved its quality control in recent years.
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