Carl Zeiss ZF.2 / ZE 15mm f/2.8 Distagon

By Lloyd Chambers Back to

Purissima Creek after Spring Rains. Nikon D3x + Zeiss 15/2.8 Distagon 1/10 sec @ f/11 Purissima Creek after Spring Rains. Nikon D3x + Zeiss 15/2.8 Distagon 1/10 sec @ f/11

The new Carl Zeiss ZF.2 / ZE 15mm f/2.8 Distagon for Nikon or Canon offers unprecedented optical performance in an ultra wide angle lens, with superb build quality and ergonomics.

Introduction
As digital camera sensor resolution increases, the demands on lens performance rise, with many lenses inadequate to the task of ultra high resolution DSLRs like the 36-megapixel Nikon D800. The exciting and newly developed optical formula of the Zeiss 15mm f/2.8 Distagon for Canon or Nikon DSLRs is an answer to those demands in the ultra-wide realm. The Zeiss 15/2.8 Distagon offers an unprecedented level of performance that makes the photographer’s job easier, because its image quality reduces or entirely eliminates the need for post-processing to correct image flaws.

Ergonomics And Build Quality
The Zeiss 15mm f/2.8 Distagon is built of metal and glass to the same superb standards as the rest of the ZF.2/ZE lens line. In this age of plastic lenses, the 15/2.8 Distagon stands out for its superb construction. It is not a small lens, but it is not an overly large or heavy lens either. It has proven to be a joy to work with. The lens balances very comfortably and naturally on a mid-size DSLR, avoiding the front-heavy and bulbous design of lenses like the Nikon 14-24/2.8G zoom.

The advanced design of the 15/2.8 Distagon requires exacting assembly tolerances. With all Zeiss lenses, a good-size sample of the first production run of both ZF. 2 (Nikon) and ZE (Canon) lenses are carefully checked for variation and MTF, to verify that construction tolerances are being fully met. Only once those preproduction lenses are fully tested is production for public sale commenced. In fact, each batch of glass has to be carefully checked for its refractive properties, because no batch is quite the same! Zeiss also checks each production lens for MTF.

Zeiss 15mm f/2.8 Distagon cutaway (actual lens cut in half!)

Design Goals

I had an opportunity to speak with Dr. Hubert Nasse of Carl Zeiss on the design goals for the Zeiss 15/2.8 Distagon. My field-shooting experience confirms that the 15/2.8 Distagon produces imagery at an exceptionally high level.

• Five (5) anomalous partial dispersion elements with special refractive properties are used for correction of color aberrations, and two aspheric elements are used to control distortion and field curvature.

• Superior sharpness to existing 14/15mm lenses. Contrast over most of the imaging area ranges from exceptional to very high even wide open, with a reduction only at the far edges and corners.

• Smaller and lighter than zooms in its range, the lens is only modestly heavier than the Zeiss 21/2.8 Distagon (740g vs 661g with caps).

• Close focus to 1:9 magnification while maintaining high performance.

• Negligible focus shift, a significant concern with high resolution digital.

• Standard 82mm filter threads, primarily intended for lens protection, with a lens front end significantly larger than the front element in order to cope with off- axis rays (to avoid image degradation).

• Avoidance of a bulbous protruding front lens element. The front element is well protected, since it is recessed significantly deeper than the lens shade. The shade even affords some protection from rain (but Zeiss Zf.2 / ZE lenses are not environmentally sealed).

• Digital sensor friendly with a very low ray angle of 11° (full frame), which is better than even the Zeiss 100mm f/2 Makro-Planar (13.6°), and much lower than the Zeiss 18mm f/3.5 Distagon (19°).

• Minimal “breathing.” The 15/2.8 varies from 15.4mm at infinity to 15.1mm at 1:9—very little change over the extreme range of focus.

• Low distortion, and a particular avoidance of wave- type distortion. The lens succeeds here with only two percent barrel distortion—minimal, and straight-forward to correct in post processing for demanding applications.

• Superior f lare characteristics. Several design iterations improved the performance prior to production, as field shots show. Even with the sun just inside or outside the frame, the level of veiling and ghosting flare remains at very low levels in spite of the 15-element design.

Bicycle at close range. Note the rich color saturation and strong lens contrast with sparkling highlights. Nikon D3x + Zeiss 15/2.8 Distagon 1/250 sec @ f/9

Color Quality
Color balance of the 15/2.8 is consistent with the rest of the Zeiss lens line—pleasing and lifelike. Due to the use of special optical glass types that eliminate most color aberrations, the color saturation is especially rich. The combination of high lens contrast and rich color saturation is stunning, and has to be experienced to be fully understood.

The digital-sensor-friendly chief ray angle means that the projected image strikes the sensor at an ideal angle of incidence, thus maintaining color consistency from the center to the corners, avoiding a color shift to cyan as seen with lenses like the Zeiss 18mm f/3.5 Distagon.

Vignetting

The Zeiss 15/2.8 Distagon has a noticeable level of vignetting wide open at f/2.8. Stopping down to f/4 evens out frame illumination substantially, and by f/5.6 it can be ignored as an issue. Although there is often negative sentiment expressed towards vignetting, this author finds it a useful tool for creative expression.

Distortion

Optical distortion is very low for a 15mm lens (2%), making it possible to photograph architecture with professional quality results as-is.

Should geometric perfection be required, the distortion curve is of a simple barrel type, which is friendly to software correction—much easier to correct than wave or “moustache” type distortion as found with most wide-angle designs.

Even at the edge of the frame, distortion is very well controlled. Because distortion is so low, the 15/2.8 Distagon is very well suited to architectural photography, as my field shots proved to me.

The blossoms are only 2-3 cm from the front lens element! Nikon D3x + Zeiss 15/2.8 Distagon 1/60 sec @ f/10
(Left) Vignetting/Field Illumination Zeiss 15mm f/2.8 Distagon (Right) Relative Distortion for Zeiss 15mm f/2.8 Distagon

Sharpness And Contrast In Real Images

Getting consistent sharpness requires a lens design that avoids sharpness-robbing practical issues like focus shift. While some ultra wide angle lenses show focus shift from f/2.8 or f/4 to f/5.6, the Zeiss 15/2.8 has no such issue, and thus one can freely focus wide open at f/2.8, knowing that outstanding sharpness and contrast will be delivered regardless of the aperture used for exposure. Field curvature is another sharpness-robbing issue; some ultra wide-angle lenses exhibit such strong field curvature that even f/11 cannot make a sharp image in some areas of the frame! The Zeiss 15/2.8 Distagon shows an impressively low level of field curvature, though it is entirely not free of it, as seen in the MTF chart. Chromatic aberrations (longitudinal and lateral) can also rob an image of sharpness. Here too, the Zeiss 15/2.8 dispels any concerns, delivering rich and saturated color, with very high contrast, a magic combination.

In short, the 15/2.8 Distagon offers extremely high performance in a very practical and meaningful sense, a fact that my field shots quickly established, leaping off the screen when viewed. Black and white shooters should take note of the exceptional lens contrast and 3D effect, which can make for gorgeous results in both color and black and white.

MTF (Modulation Transfer Function)

Contrast on coarse and fine structures in the central 1⁄2 area of the frame is extremely high, dropping gracefully to still very high levels to the edges and corners. For a 15mm lens, this level of performance is world-class and is very good even when compared with lenses of longer focal lengths.

When one notes that the contrast as seen in the MTF graph is influenced by some small but unavoidable curvature of field, and that it is for white light, the actual performance on real “3D” images and/or those of singular color can be even higher than the MTF chart would suggest. Real-world images show an unusual brilliance.

MTF charts for Zeiss 15/2.8 Distagon)

Depth of Field

Working with the 15/2.8 Distagon in the field on my Nikon D3x and Nikon D800, I confirmed that depth of field even with a 15mm lens is strictly limited as expected. The assumption that a 15mm lens has “huge depth of field” is an enduring misconception, but experience shows that with the ultra high performance of the 15/2.8 Distagon on a high resolution DSLR, even small focusing errors will show less than the lens is capable of. With high optical performance comes a requirement for the photographer to realize the potential of the lens. (See also Diffraction in the January/ February 2009 PHOTO Techniques, because stopping down is not a simple answer).

As shown in the DOF table for the Zeiss 15mm f/2.8 Distagon, at f/8 with the lens focused at infinity, peak sharpness for 5-micron circle of confusion (e.g. Nikon D800 resolution) extends from 5.93 meters (19 feet) to infinity. And this is with a 15mm lens! Thus dies the fable of “huge depth of field”.

Depth of field table for 15mm lens using 30 micron and 5 micron Circle of Confusion (COC)

Working With The 15/2.8 Distagon In The Field

It is very enjoyable shooting the 15/2.8 Distagon on a camera like the Nikon D800 or Canon 5D Mark III. The lens balances well and the manual focusing smoothness and “throw” is a pleasure to use. With a 15mm lens, one must seek out appropriate subjects suitable for an ultra wide angle, such as tight spaces or strong geometric forms. The ultra-wide angle of view also demands careful composition to fill the frame without producing large areas of uninteresting filler— this calls for a strong foreground, or getting in closer (e.g., a tight interior space or similar).

The bright f/2.8 aperture and high lens contrast makes it relatively easy to focus by eye, but the use of zoomed- in Live View is the smart move to extract every bit of sharpness by virtue of exact focus. Live View reveals the strikingly high performance; zooming in shows a remarkable clarity compared to most lenses, which makes focusing in Live View mode particularly easy.

Field shooting experience suggests that f/5.6–f/8 provides the most useful blend of peak brilliance and depth of field, but aside from a margin for focusing error, the only reason to stop down is for deeper depth of field. Shooting wide open at f/2.8 can be useful to tone down off-center bright subject matter like clouds. Stopping down to f/11 begins to show the contrast-robbing effects of unavoidable diffraction, but the inherently high brilliance of the 15/2.8 Distagon preserves f/11 as an eminently usable aperture. However, f/16 shows a significant loss of contrast (via diffraction) relative to the ultra-high performance at more modest apertures, and f/16 is thus best avoided when one desires the highest contrast and sharpness with a high- res digital SLR.

California Buckeye. Outstanding lens contrast lends itself to black & white conversion. Nikon D3x + Zeiss 15/2.8 Distagon 1/60 sec @ f/11

Conclusions

The Zeiss 15mm f/2.8 Distagon delivers a level of optical performance and build quality commensurate with its price. Connoisseurs of ultra wide angle photography will find the Zeiss 15/2.8 Distagon a compelling and satisfying investment in their passion.

Resources: Carl Zeiss Inc.: zeiss.com

Editor’s Note: All Zeiss DSLR lenses are designed for cameras with 24X36mm sensors. See the full interview with Dr. Hubert Nasse at http:// dgly.org/nasse15.


About the Author

Lloyd Chambers
LChambers
Lloyd L. Chambers enjoys all-digital photography after shooting film for years in 35mm, 4 X5, 6 X7 and 617 formats. His web site diglloyd.com offers a wealth of material on advanced photographic techniques, and his Making Sharp Images is a reference work on sharpness and blur of all kinds.