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07-29-2008, 03:21 PM   #31
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QuoteOriginally posted by deudeu Quote
I don't know if it is distortion but the two buildings on each side look like they are leaning...
When the camera is not horizontal, you get converging verticals with any lens. It is most obvious with short focal lengths.

The distortion we're talking about are curved lines that should be straight.

07-29-2008, 03:27 PM   #32
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QuoteOriginally posted by Ben_Edict Quote
There is some visible distortion, but I have yet to see any other super-wide angle, that is free from this kind of distortion.
It has certainly been alleged that the Pentax 12-24 draws straight lines at the edges of the field, straighter than the Sigma 10-20, and this may be so. For nearly double the price, it ought to be.

But until those that choose to participate in the debate understand that the rendition of straight lines is a different issue from the converging verticals that are normal with any wide-angle lens pointing up or down, it's unlikely that any actual sense will come from this thread.
07-29-2008, 03:34 PM   #33
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QuoteOriginally posted by ChrisA Quote
It has certainly been alleged that the Pentax 12-24 draws straight lines at the edges of the field, straighter than the Sigma 10-20, and this may be so. For nearly double the price, it ought to be.

But until those that choose to participate in the debate understand that the rendition of straight lines is a different issue from the converging verticals that are normal with any wide-angle lens pointing up or down, it's unlikely that any actual sense will come from this thread.
I am pretty sure that the building on the left looks like it is leaning more towards the top than it is towards the bottom...
Grab a ruller and chech for yourself... It may be slight, but there is some distortion.
07-29-2008, 05:37 PM   #34
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QuoteOriginally posted by deudeu Quote
I am pretty sure that the building on the left looks like it is leaning more towards the top than it is towards the bottom...
Grab a ruller and chech for yourself... It may be slight, but there is some distortion.
Are you referring to the house I posted? If so, you may be right. I didn't use a spirit level, since I was just intending to illustrate the barrel distortion.

I took this one and this one as extreme examples of converging verticals.

But all that aside, the barrel distortion from the 10-20 results in curved renditions of straight lines. With converging verticals, which is not distortion as such, they are still straight.

07-29-2008, 06:03 PM   #35
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I have the 10-17 fisheye and 12-24, so I know both barrel distortion and converging verticals. I've never noticed any barrel distortion with the 12-24.

That house picture up the post sure has something going on, though.
07-29-2008, 08:24 PM   #36
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QuoteOriginally posted by ChrisA Quote
Can you see it in this? It looks pretty obvious to me. Look at the left and right vertical edges of the house. Trust me, they're straight in real life.


If comparing the two lenses' distortion is the point of this discussion, doesn't it make more sense to be posting examples of the Sigma 10-20mm at 12mm instead of 10mm?

Thank you
Russell
07-30-2008, 02:55 AM   #37
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QuoteOriginally posted by Russell-Evans Quote
If comparing the two lenses' distortion is the point of this discussion, doesn't it make more sense to be posting examples of the Sigma 10-20mm at 12mm instead of 10mm?
Yes, absolutely. I only posted the picture to illustrate the barrel distortion as an obvious example of it (because someone said they couldn't see it), not at all to compare the two.

I'm not at all knocking the Sigma 10-20 - I've been very pleased with it, and it's a lot more affordable than the Pentax.
07-30-2008, 02:58 AM   #38
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QuoteOriginally posted by deudeu Quote
I don't know if it is distortion but the two buildings on each side look like they are leaning...
Yup it is distortion!

This being said, if anyone can find me any lens wider than 20mm that is totally free of distortion, please enlighten me!
This is the simple perspective "distortion", when take a photograph from the ground looking upwards. It is very different from the barrel distortion shown in ChriusA's image.

At the end of the day "perspective distortion" is no distortion at all, but a simple effect of the photographer's physical standpoint and the angle of the camera.

Ben

07-30-2008, 03:45 AM   #39
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Attempt at a summary

How to choose between these two wide angle zooms? Depends on your priorities and your application. I decided to update my original post, for my own benefit if not for anyone else's. Don't mean to open up the can of worms again.

Priorities:
1. Wide field of view? Sigma has 10mm versus 12mm.
2. Narrow field of view? Pentax has 4mm more in the "long" end.
3. Money? Sigma is cheaper.
4. Speed? The Pentax at 12mm f/4 is already performing at its best. And it's constant f/4 all the way through the zoom range.
5. Sharpness? The Pentax is sharper towards the edges than the Sigma, unless you stop down to f/8 or so.

Application:
1. Landscapes? If you are careful with your composition you won't find the Sigma barrel distortion at the edges disagreeable.
2. Architecture or other geometrics? Pentax has less edge distortion but the Sigma from 12mm is fine.
3. Interiors? The Pentax is faster and sharper wide open. But if you're using a tripod you can stop down.

Both these lenses have mustache distortion that is not going to be correctable and CA that is.

Jury is still out on other aspects like colour rendition or bokeh.

Future choices might include the Tokina AF 11-16mm f/2.8 if Pentax clones it. This has 2% barrel distortions wide, but highly impressive resolution and might be better for interiors, being one stop faster. There's also the Tamron 10-24mm f/3.5-4.5, currently in development. This will cover the widest range of the four lenses.

Currently the full frame Sigma 12-24mm F4.5-5.6 EX DG ASPHERICAL HSM is also available. It's bigger and 50% heavier. Not too much discussion about it on Pentax forums.

Outside the Pentax box, consider a full-frame camera if your bread and butter is wide-angle.

References:
Pentax DA 12-24mm f/4 AL ED [IF] test report.
Sigma AF 10-20mm f/4-5.6 EX DC test report.
Tokina AF 11-16mm f/2.8 AT-X Pro DX Canon test report.
Tamron SP AF 10-24mm f/3.5-4.5 DI II LD Aspherical (IF) announcement.
07-30-2008, 03:46 AM   #40
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QuoteOriginally posted by Ben_Edict Quote
At the end of the day "perspective distortion" is no distortion at all, but a simple effect of the photographer's physical standpoint and the angle of the camera.
Agreed! Unfortunately the term "distortion" is applied loosely.
07-30-2008, 10:29 AM   #41
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QuoteOriginally posted by madbrain Quote
I own a Sigma 10-20 with a K200D . I can attest that there is significant distortion. You have to be really careful not to take people with it.

FYI I took those shots on purpose as a joke .
Thanks, madbrain, for the tips. I will take extra care when taking wide angle shots with people in it. Also, having said that, the long end of 24mm FL suits me better than the 20mm in sigma as it is close to normal shots when I get close enough. I feel that the 12-24mm range is more useful for my purpose as a "street" or walk-around lens. That is just personal opinion. My friend has the 10-20mm sigma and it is tack sharp, one of his favorite lens.

QuoteOriginally posted by ChrisA Quote
Yes, absolutely. I only posted the picture to illustrate the barrel distortion as an obvious example of it (because someone said they couldn't see it), not at all to compare the two.

I'm not at all knocking the Sigma 10-20 - I've been very pleased with it, and it's a lot more affordable than the Pentax.
ChrisA, I purchased this lens recently from a fellow Pentaxforum member, it is actually cheaper than a brand new sigma 10-20mm for me; lucky for me anyway.

QuoteOriginally posted by rparmar Quote
Agreed! Unfortunately the term "distortion" is applied loosely.
rparmar, I agree with your comment too. The converging line "distortion" happens in any wide angle lens to various degrees. And it is up to us to make it look less "distorted".
08-13-2008, 08:22 AM   #42
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Between 12mm-20mm, which one has less distortion?
I am having Sigma 10-20mm but if the Pentax one has less distortion, I would probably switch to Pentax ^_^.
Thanks.
08-13-2008, 03:24 PM   #43
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QuoteOriginally posted by aleonx3 Quote
Here is an example of the Pentax 12-24mm at 12mm end, do you see any barrel distortion? again, this is only 12mm not 10mm as the sigma can provide.
That's not a great example as that is also perspective distortion (converging verticals) as your camera is near ground level and the tops of those buildings are nowhere near. The earlier house shot from the Sigma is a better indication as it is relatively straight-on.

I've heard pretty much nothing but good things about both lenses and there are plenty of good reasons to use either--there's no need for any holy war. I like constant f/4, and I like that it zooms to 24mm. For one thing, this allows pretty good kit pairing with film-compatible zooms starting at 24-28mm. Exactly zero percent of my images are at 10mm or 11mm as I have never had a lens that shoots that wide--so I can't say I really miss it.
08-13-2008, 07:52 PM   #44
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"....Tamron 10-24mm f/3.5-4.5"

I friend of mine that is a Pro has had his hands on one of these in another mount. I'm not sure if it was a production model or not. He did some testing with it and was very impressed.
08-14-2008, 10:11 AM   #45
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My widest (exempt the kit lens) is the FA* 24/2, a very fine lens.

It represents a 36mm on a full frame, I would say a forgotten standard wide angle. Because it has F2 its good for indoor reportage, available light, also most flashes do good with a 24mm.

I could do with a 12-24 to go with my FA* 24/2. specially for landscapes.

Gues I would miss the 20 tot 24mm more then the 10 tot 12mm's.

But of course its a matter off taste.

Guido
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