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

Close Focus and Bokeh

One of the most interesting and exciting ways to use UWA lenses is to get extremely close to your subject and creatively frame an image through the ensuing distortion. That, and is the magnification is large enough, then "environmental macro" images become a possibility where a small subject can be focused on closely but its surroundings and the scene itself are captured as well. This is as opposed to just a bug (or just its eye) filling the entire frame like with traditional macro lenses that are telephoto in nature.

Focusing Distance vs Working Distance

Before we get to the comparisons we wanted to reiterate what the minimum focus distances were in case you skimmed over that part on the Specifications page:

• Pentax DA 10-17mm FE - 14 cm / 5.5 in
• Rokinon 8mm FE - 30 cm / 11.8 in
• Sigma 8-16mm - 24 cm / 9.4 in
• Rokinon 10mm - 25 cm / 9.84 in

What most people don't realize, however, is that Minimum Focus Distance and Minimum Working Distance are not the same. Using a recent promotional image of the Pentax K-1's Shake Reduction II system, ignore the light blue curved arrows depicting the five axes the SRII system affects. Instead, focus on the yellow, green, and orange arrows:

The yellow arrow, which spans the distance between the sensor and the subject, is the Focusing Distance. The green arrow, which is between the front of the lens and the subject, is the Working Distance. Depicted in orange, the space in between includes the total length of the lens as well as the mount and mirror box within the camera, which is still part of that total focusing distance. In other words, 5.5 inches (14 cm) is not the amount of breathing room available to you from the tip of the Pentax zoom's embedded lens hood, for example.

What this minimum working distance looks like in reality is best demonstrated visually:

All these lenses can be considered "close focusing," but the Pentax zoom stands alone with just how close you can get. Essentially you are almost touching the front element!

In theory, the fisheye zoom should have remarkably shallow depth of field. Even compared to the rest, this is because of its ability to focus so close despite not having the fastest aperture. Let's see if that holds true...

Beach Reeds Comparison

The below series placed the "elbow" of the broken reed in the same location within the frame regardless of the lens (top-right "third" intersection). Focused at the minimum focusing distance for each optic, we wanted to quickly emphasize how incredibly difficult it was to do so for the two fisheyes. Using Live View and Focus Peaking while atop a tripod, it was no easy feat. Conversely, the two rectilinear lenses quickly allowed us to achieve critical focus.

Despite being the furthest away, the hardest by far to focus at this distance was the Rokinon 8mm FE.

All of the shots for this series were taken using the below settings:

F2.8
F3.5
F4.0
F4.5
F5.6
F8.0
F11

And lastly, here is a direct 4-way comparison of each lens at their widest aperture:

The full set of 23 RAW images can be downloaded here (573 Mb).

Verdict

We knew that the Pentax would have some interesting results once we got into the field after realizing just how close it could focus, but we weren't prepared for just how stark those differences would be. The two rectilinear lenses look pretty identical save for the much shallower depth of field provided by the 10mm's wide open aperture of F2.8.

Because of its ability to focus within such a short distance, the Pentax had shallower depth of field at F11 than its fisheye rival wide open (F3.5). And then of course the same applies to it vs the Sigma zoom wide open. The Rokinon 8mm FE was the least exciting in this regard, but both it and the Sigma should in no way could be considered true close focusing lenses. The Rokinon 10mm's saving grace, despite sharing a near identical minimum focusing distance to the 8-16mm, is its aperture of F2.8 that does in fact allow for attractive bokeh and a relatively shallow depth of field.

But again, the Pentax reigns supreme here with gorgeous blur and a very visible 3D "pop" thanks to its magnification, incredibly shallow DoF, and rich colors.

Regardless of which lens you use, it's important to note that when being creative in this way, especially the Pentax 10-17 FE, it's easy to get tunnel vision and ultimately lost in the moment as you try to compose through the viewfinder. Because the low magnification will make it difficult to assess the true distance from the front element (and in reality make you feel like you are further away than you actually are), you can damage and scratch that bulbous front element before you realize just how close you are!

Continuing along, the next chapter covers vignetting and our rather unique test for it.