[JoepLX3]

other than the focal length advantage of the Tamron, it fell short on the IQ side of things. for most people here, IQ is more of a top priority.

Just having bought the Tamron, do I want to look at IQ comparisons with the Sigma?

[Steve Beswick]

If it doesn't need to be a zoom, you could buy both the 8mm and the 14mm Samyang for roughly the same amount of money.

[Pentaxor]

Just having bought the Tamron, do I want to look at IQ comparisons with the Sigma?

if the Tamron image results work for you, I dont think there would be a need to. especially if your priority is the focal length zoom range.

[JoepLX3]

if the Tamron image results work for you, I dont think there would be a need to. especially if your priority is the focal length zoom range.

How is IQ defined by the Sigma fanclub?

Comparison to other wideangle zooms we've tested recently suggests the Sigma's class-leading days may be numbered. On APS-C, it simply can't match the biting central sharpness of the Tamron in the 10-18mm range (for which, we suspect, users will mainly be buying this type of lens), and has more problematic distortion characteristics. However in a typical case of swings and roundabouts, the Sigma shows superior sharpness when shot wide open, and is better in the corners of the frame at all settings; it also has lower chromatic aberration, is better built and uses a superior focusing system.

I weight "Rather inconsistent sharpness (partially due to curvature of field) + pronounced, complex distortion at 10mm" on the Sigma pretty heavy, as well as the strong points of the Tamron "Low distortion + Generally good resistance to flare". But on the other side (imho less important) there seems to be "Very low chromatic aberration "versus "Soft wide open (low local contrast) + Soft corners at all focal lengths and apertures".

Or is the IQ statement based on the much more expensive Sigma 10-20 mm F3.5?

[GeneV]

I love the lens. I was pleasantly surprised by the low distortion levels and the Pentax image quality. I have not yet been disappointed by the field of view at 12/18mm, but no doubt will decide it is not yet wide enough in a few years.

That's been my experience. If I decide it's not wide enough, then the 8-16 makes sense.

On the urban side, I would also find this lens much less useful if it did not go to 24mm. That is an excellent street shooting FOV.

[Biro]

Well, I actually dragged myself into New York an hour early today and dropped in at B&H Photo as they were opening. I checked out the Pentax 10-17 fisheye, the Pentax 12-24, the Sigma 8-16 and both verisons of the Sigma 10-20 on a K-7 body. And I walked out with... the Pentax 12-24.

The Sigmas were fine, nice build quality and all. I can certainly understand why many Pentaxians go for them. For me, while the difference between 10mm and 12mm was definitely noticeable, it wasn't dramatic. I walked around the store and found that, in nearly all cases, a single step back compensated for whatever wide-angle shortcomings the Pentax 12-24 had vs. the Sigma 10-20.

I also liked handling the Pentax better. It was smaller than the f/3.5 version of the Sigma 10-20 but a bit heavier and "denser." But the Pentax was actually smaller and lighter than I imagined - certainly smaller and lighter than my DA* 16-50. I was exepecting it to be about the same.

The Sigma 8-16? Now there's a lens that had some real appeal to me... and if I ever decide that the Pentax isn't wide enough, that's the lens I'll be going for. But, in this case, the Sigma's slower speed (f/4.5-5.6) and my natural tendency to opt for a lens that's the same brand as the camera body won out.

B&H sales staffers don't work on commission, so they don't try to hustle you into something you don't want or need. My guy firmly supported opting for the Pentax 12-24. No lens is perfect and I can certainly understand why anyone would would buy one of the Sigmas. In this particular case, it was the Pentax for me. Thanks everyone for all your input and help.

[typical8o8]

nothing like going out there and actually getting the answer yourself. seems like a dying practice in the age of the internet.

[JoepLX3]

nothing like going out there and actually getting the answer yourself. seems like a dying practice in the age of the internet.

Sometimes in the shop you make impulse decisions, because besides handling (which also is important) it can be difficult to compare things well in such limited time / space...

For me, while the difference between 10mm and 12mm was definitely noticeable, it wasn't dramatic. I walked around the store and found that, in nearly all cases, a single step back compensated for whatever wide-angle shortcomings the Pentax 12-24 had vs. the Sigma 10-20.

I think you totally missed the point of UWA. To my opinion UWA have summarized two purposes:

1. Get everything in the picture when you can't take a step back
2. Geometrical effect on a picture that cannot be imitiated by another focal lenght and taking a step back
   • Do the experiment with your kit lens (if you want in combination with the UWA), change your zoom and compensate by your feet to capture the same scope. Then look at your results!!!
   • If 2 mm is a lot at ~18 mm then it is actually even more significant at 10~12 mm!!! (and/because much less at 50-55 mm)

Probably the Pentax 12-24 will be just fine for you, because if you don't have both then it will be difficult to compare either way. Did you also notice / try out the Tamron 10-24?

[JoepLX3]

For sake of completeness, I did some searching (effect seems to be most obvious at Fisheye and Portrait applications, but for sure also at UWA):

Simple / theoretical explanation + "dry" examples
http://en.wikipedia.org/wiki/Perspective_distortion_(photography)

Impact on Portraits
Digital Photography Tutorial: Focal Length - TrustedReviews - TrustedReviews

A simple fisheye example
http://www.photography.com/articles/basic-concepts/perspective-distortion/

Two extremes
http://static.photo.net/attachments/bboard/00C/00CSy3-23993284.jpg

How to correct distortion
http://www.lonestardigital.com/perspective_correction.htm

Old discussion on this forum on same subject
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/36957-focal-le...n-tools-2.html

Oh, my intension is not to say the Pentax 12-24 is a bad pick

[Rondec]

It is interesting. I don't own any of these lenses -- not really a wide angle shooter, but looking at Amazon's web site, it appears that the Sigma at 10mm takes in 102 degrees angle of view, while the Pentax at 12mm takes in 99 degrees. That just doesn't sound like a whole lot to me, but I guess at close quarters maybe it would make a difference.

The things that impress me about the Pentax 12-24, looking at photos, is the control of the distortion and the sharpness of the photos.

[Biro]

It is interesting. I don't own any of these lenses -- not really a wide angle shooter, but looking at Amazon's web site, it appears that the Sigma at 10mm takes in 102 degrees angle of view, while the Pentax at 12mm takes in 99 degrees. That just doesn't sound like a whole lot to me, but I guess at close quarters maybe it would make a difference.

The things that impress me about the Pentax 12-24, looking at photos, is the control of the distortion and the sharpness of the photos.

Exactly. My decision had to do with balancing distortion and image quality vs. the usefulness of an extra 2mm at the wide end. I appreciate Joe's remarks and I fully understand the spirit in which they are offered. But I didn't miss the point of UWA, it's just that the Pentax 12-24 was a better compromise - for me.

If I went from 10mm to 12mm with the Sigma, there was still less distortion at 12mm with the Pentax - even when panning the lens up and down. You won't see leaning buildings and trees with the Pentax. And I found while it was nice that the Sigma did offer a few more degrees of view, I could still get an entire room in the frame with the Pentax. As for landscapes, we'll see... but as long as I'm not standing with my back at the edge of a cliff, I think I'll be fine. But one never knows, right?

As I said earlier, I can certainly understand why many other Pentaxians have gone for the Sigma. Still a great deal at the price and you won't find me putting it down. But if I discover I need/want more of a wide-angle view in time, it would probably be the Sigma 8-16 that I would be looking for.

[Jewelltrail]

Rondec It is interesting. I don't own any of these lenses -- not really a wide angle shooter, but looking at Amazon's web site, it appears that the Sigma at 10mm takes in 102 degrees angle of view, while the Pentax at 12mm takes in 99 degrees. That just doesn't sound like a whole lot to me, but I guess at close quarters maybe it would make a difference.

AOV you report here is using the Sigma sensor--not an apples to apples comparison and this issue on this forum is as perennial as the grass. Appples to Apples will give you these numbers for the Sigma lens: Angle of View : 109.4 - 70.5 degrees.

For example:
Sigma 10-20mm F4-5.6 EX DC (Konica Minolta and Pentax mounts)

[Eruditass]

I would've probably gone for the 12-24mm if it was the same price in K-mount as other mounts...

[CWyatt]

Note that the image only compares FOV, and does not take into account the changes in perspective and the 'compression' effect of longer lenses.

What compression effect?

[Rondec]

Thanks for the correction. I took the numbers from the listing for the K mount version of the Sigma 10-20 on Amazon, but I guess it must be listed incorrectly.