[clackers]

We probably have exhausted the subject...

But I would like to mention that folks with a K-1 can look to at least one real, FF UWA option that is generally available used or as a refurbished (how I got mine) - the Sigma 12-24.

Unlike you, I have both a K-1 and the Sigma 12-24.

I agree with that quoted article's finding that in real life sharpness shots, "The Pentax [DA12-24] lens consistently performed better than the Sigma throughout the zoom range and regardless of f-stop."

However, the Sigma on FF is 12-24, not 17-24, so that's why I bought it this year, also refurbished, from Sigma in the States.

A couple of shots with it. Plenty of flare and chromatic aberration in the backlit left part of the first picture, but that's to be expected with these bulbous front elements. The Pentax's is less prominent and can in fact take a screw-in filter.

If you don't understand, just ask me or anyone else, we'll help you, but please stop bluffing your experience or knowledge!

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Last edited by clackers; 12-23-2017 at 02:40 AM.

[UncleVanya]

A couple of shots with it. Plenty of flare and chromatic aberration in the backlit left part of the first picture, but that's to be expected with these bulbous front elements.

I really love the second shot. Great composition.

[ScooterMaxi Jim]

Yep, I get it. From my considerable experience I also get that using filters on UWA lenses create more problems than they resolve, and the Sigma is perfectly capable of taken rear gelatin filters if you feel the need. We can do considerably better using modern PP techniques. Also, the Sigma works perfectly well on film cameras (FF), even though I don't have the K-1.

As for the conclusive findings in the PF review indicating that the Sigma is the superior optic - the evidence presented - especially regarding the vastly superior CA performance for the Sigma - speaks for itself. You might have gotten a bad copy of the lens (quite common, given the exotic design), and should have sent it back if it fell short of your standards.

[clackers]

As for the conclusive findings in the PF review indicating that the Sigma is the superior optic - the evidence presented - especially regarding the vastly superior CA performance for the Sigma - speaks for itself.

Let me give you the words on sharpness from the link you provided - if you want to dispute their results, best take it up with the authors:

Conclusion

The results of the Edmund Resolution Power Chart were very interesting. Initially, the Sigma DG 12-24 f/4.5-5.6 slightly out-performed the Pentax DA 12-24mm f/4. However, once the Pentax lens was either stopped down beyond F4 or zoomed beyond 12mm it performed marginally better than the Sigma. The Tamron came in third.

The field sharpness test told a different story. The Pentax lens consistently performed better than the Sigma throughout the zoom range and regardless of f-stop. The Tamron again came in third place.

You might have gotten a bad copy of the lens (quite common, given the exotic design), and should have sent it back if it fell short of your standards.

You can see my pictures above, it's not decentred. I like it.

My Pentax is sharper and faster, my Sigma is wider, this tallies with the official review by this forum you've already quoted, case closed despite your protests, right?

Perhaps, James, you have pictures of your own to show that both Pentax Forums and I have this the wrong way round ... that by coincidence, we both received dud copies. Side by side on film of the same subject with your Sigma and Tokina, you know, controlling variables, all that boring stuff required of legitimate evidence ....

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Last edited by clackers; 12-24-2017 at 01:25 AM.

[clackers]

Yep, I get it. From my considerable experience I also get that using filters on UWA lenses create more problems than they resolve

Well, since you're so interested in my feelings about filters ...

Caps vs UV filters - PentaxForums.com

[ScooterMaxi Jim]

The conversation gets a bit absurd outside of the APSc context. The Tokina/Pentax design is limited to 90 degrees horizontal FoV on crop sensor. The Sigma was designed for FF yielding an expansive 122 degree FoV - so the marginal difference in resolution from an exotic design is a given. Yet, despite the greater demands on the lens design, the Sigma is far superior in CA and lack of distortion.

The review gives the Sigma a 9.0 (excellent) rating, Pentax an 8.8 (very good) rating - playing on the latter's turf. The retail price at time of review was $829.95; that price is now roughly halved... So, the review conclusion:

If you have an unlimited lens budget, the Sigma DG 12-24 f/4.5-5.6 is the perfect choice. The lens has the least barrel distortion, vignetting, chromatic aberration, and is reasonably sharp. Why wouldn’t you buy a lens that already addresses some of the major problems of ultra-wide angle zooms?

For me, I can tolerate only so much CA, and software correction always leaves defects when the problem is so severe as in this Tokina lens design. The review sums it up correctly:

The Sigma DG 12-24 f/4.5-5.6 was the clear winner. Not only did it have very limited chromatic aberration wide open but it was consistent throughout the f-stop sample. The Tamron SP AF 10-24mm f/3.5-4.5 DI II displayed some chromatic aberration at f3.5 but improved significantly at f8 and f16. The Pentax DA 12-24mm f/4 did not do as well as the other two lenses, which was surprising. Not only did it have significant chromatic aberration at f4 but it did not improve much as the lens was stopped down.

My experience with the Tokina version of this lens (on Canon) was not so severe, but still is considerably worse than the Sigma (second sample). These UWA lenses exhibit extreme CA with only very minor decentering. This is why you get such varied test results in credible testing (especially apparent with the Sigma). It is quite certain that if you are finding greater CA on the Sigma, you have a slightly decentered copy, unfortunately.

---------- Post added 12-24-2017 at 11:34 AM ----------

Well, since you're so interested in my feelings about filters ...

Caps vs UV filters - PentaxForums.com

Good discussion, and some nice images in that thread. Filters are helpful for the kinds of situations you posted.

Believe me, I use filters when I have the need. Way back when when I was working in a camera shop, we got great deals on fully coated filters (typically Hoya back in the days when their filters were much higher quality) because the retail mark-up was huge, and employees got them for cost+10% - $80 filters for $9, etc.

The problem with even thin filters on UWA is angle of acceptance. That's why you see the bulbous outer elements - they can manage the angle better - closer to perpendicular. Obviously, front filters are flat, causing optical degradation in the UWA field due to the severe angles involved. At least gelatin filters mounted at the rear are very thin and are less of an optical challenge. Frankly, I've never bothered with them, though, so I can't say if they are an effective solution.

A second problem is how polarizers work in sunny conditions at UWA. As is quite obvious, the effect of polarization varies considerably depending on angle to the light source (the sun). This results in increasingly uneven impact the wider the FoV. On UWA, it is almost always unnaturally distracting, and very difficult to fix in post. It can be interesting left alone as a special effect, but not my cup of tea.