Rokinon 8mm vs. 10mm vs. Sigma 8-16mm vs. Pentax 10-17mm Ultra-wide Showdown

Chromatic Aberrations

The final variant of aberration that we will assess comes in the form most commonly referred to as "purple fringing." With more and more lenses being fitted with specific glass elements to mitigate the effects of such unpleasantries, the industry standard has certainly moved closer to their total elimination, including from a lens' widest aperture.

So how does this lens collection fare with keeping the amount of fringing, well, to the fringes?

Chromatic Aberration Comparisons

Using scenes we've already visited during our many field of view and distortion comparisons, we wanted to take a closer look at a couple of them.

First, The Chamberlin:

proved one of the easiest comparisons to induce this unwanted effect. While the two rectilinear lenses at the bottom didn't have the field of view to show the railing to the left and right, the two fisheyes both failed to completely keep the Fringe Monster from rearing its ugly head. For reference, these crops (100% when enlarged) were taken from the right of the frame where the back of the chair crosses in front of the white guard rail. On the left is the Rokinon FE prime and the Pentax is on the right:

Also something to keep in mind - that was shot at F8.0, so no where near wide open for either lens.

For the next set, we'll revisit this hangar of restored aircraft:

Using the windows along the upper part of the back-right wall, which features backlit window panes, it is a very common situation when it comes to where seasoned photographers know to be on the look-out for CA. Here is how the set fared, again at F8.0 as that was how the series was shot:

Now, we recognize that the above pair of scenes were taken at F8.0. The following series, however, includes a comparison by aperture in order to sate your curiosity. Additionally, this time we designed this test to incorporate backlit tree branches, arguably the most egregious offender when it comes to eliciting chromatic aberration. Using the following scene:

the below settings were in effect throughout this series:

  • Camera: Pentax K-3
  • Tripod Used: Yes
  • Tripod Leveling: Horizontal
  • Focus: House Directly in Image Center
  • 2s Timer per shot
  • Shake Reduction: Auto Off (2s Timer)
  • Mirror Lock-Up: Auto Up (2s Timer)
  • Capture Mode: RAW (.DNG)
  • Camera Mode: M (Manual)
  • Aperture: F2.8-F11
  • ISO: 100
  • AA Simulator: Off
  • In-Camera Corrections: Off
  • Flash: No On- or Off-Camera Flash

Here are the 100% crops from the yellow box above:

F2.8

F3.5

F4.0

F4.5

F5.6

F8.0

F11

The full set of 23 RAW images can be downloaded here (633 Mb).

Verdict

With regard to purple fringing, there are clear winners and losers. Or more specifically, loser.

The only thing the Pentax zoom would be competitive in winning would be "which lens has the most atrocious purple fringing of any lens we've ever tested?" Wide open until F5.6 there is minimal improvement and even by F11 it was still present and in force, a fact confirmed without viewing the 100% crops.

The other fisheye likewise exhibited CA for the majority of its aperture range, however it was significantly more controlled and at times negligible. The same couldn't be said for the Pentax fisheye where in images that had large swaths of it (like the Chamberlin railing at the top of this page), the white balance of the entire frame was affected, giving a strong hue of blue to the overall image.

Conversely, we are still blown away by the rectilinear lenses, most notably the Sigma zoom. There's not much else to say about those two that the above series didn't speak volumes about - the 10mm prime does very well starting from F2.8. The 8-16mm, despite its late entrance starting at F4.5, is nothing short of superlative - mitigating any possibility of chromatic aberrations regardless of the aperture.

The great news for owners and prospective owners of the Pentax 10-17mm fisheye (and to a far lesser extent the Rokinon FE too) is that chromatic aberration is highly correctable and it's surprisingly easy to do. Thanks to advancements in post processing software, Adobe Lightroom for example, requires a few seconds in order to transform the once-maligned images to devoid of all CA just like the "Before/After" animations we had at the top of this page. For one last such demonstration, we used the most vibrant instance of purple fringing from the by-aperture comparison above. Here is the Pentax fisheye wide open (F3.5) before and after being corrected with just one click:

BEFORE
AFTER

But there's always a "but" - because of how thick and vivid the fringing can be from the DA 10-17mm FE, the "CA bleed" can be so heavy that sometimes the only saving grace for image quality sticklers is to convert to black and white. This is especially true at high ISO when the CA mixes with the noise/grain as well as components of an image that don't have clean edges. Truth be told it isn't very common, however in years of ownership across a myriad of shooting situations, our reviewer has found it to certainly be a realistic possibility.

Here is one such example, featuring a 100% crop from a wedding using the Pentax K-3 and matching fisheye that has some aberration remaining. On the left look along the Fire Extinguisher text as well as one man's hair just under the glass. Also pay attention to the clothing of the two seated gentlemen (backside of one's arm and along the top of the suit jacking hanging on the chair) on the right side:

Image B

The last segment of optical analysis follows with the "Sharpness" chapter.


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