Tokyo video production group Ellroy Inc. carry out a thorough hands-on investigation to compare the ZK zoom lenses with prime lenses.
When Fujinon developed the ZK Series, the goal was to create a zoom lens with optical performance on a par with that of a prime lens. To see whether this ambitious goal was achieved, Tokyo video production group Ellroy Inc. carried out a thorough hands-on investigation. The pros at Ellroy use single-focus prime lenses on a daily basis and have extensive experience of shooting video and still images at 4K and even 6K resolution. They looked to tackle a common perception among creators in the advertising industry: the idea that zoom lenses, for all their undoubted functionality, can fall short when it comes to image quality. Would the ZK Series be able to flip that notion on its head?
Comparing image quality with that of prime lenses Assessing the optical performance of cine zoom lenses
“What’s the ZK Series really like in terms of quality? If we want to go beyond the specs in a brochure, how can we independently assess the lens performance?” Such was the mindset of the Ellroy team members who carried out verification shoots to compare ZK Series lenses to single-focus PL-mount cine lenses with high optical performance. (PL-mount cine lenses are among the most commonly used lenses in the advertising industry.) Ellroy also used ZK Series lenses for actual ad shoots and performed a variety of different quality checks. Participating in the verification process was Ellroy’s shooting and editing team, which included a director, lighting and editing specialists, and a shooting assistant—all led by photographer Kazumi Takahashi, a 10-year veteran of the industry. Verification testing focused mainly on resolution and distortion. The team also performed a variety of shoots to investigate the lenses’ handling of color, an area where every lens displays unique characteristics.
ZK Series lenses naturally offer excellent zoom functionality, but what really sets them apart is their full support for 4K shooting. Ellroy uses 4K cameras such as the Red Epic Dragon and Sony FS7, so shooting in 4K and 6K is part of the company’s daily workflow. They know from experience that, when it comes to achieving the best possible high-resolution shooting performance, the lens is just as important as the camera itself.
With the above in mind, Ellroy’s first step was to verify the resolution of the ZK lenses by testing them in comparison with a prime lens. When Ellroy staff were testing the Fujinon lenses, the benchmark for 4K performance was a TVL (horizontal resolution) of greater than 2000 as measured on relevant charts. With regard to T-numbers, for each lens two patterns were configured corresponding to a maximum aperture value and a T2.9 value. Testers also shot footage of a female model and compared various aspects of sharpness, including lines, text, skin, and hair.
First up in the test was a pattern corresponding to a T-number of 2.9. If you look at the center chart, the image resolution of the PL-mount prime lens is indistinguishable from that of the ZK Series lens. What’s more, when you consider the sharpness of the bold lines and text on the periphery of the chart (i.e., in the four corners), you could even say that the ZK Series is superior.
For the comparison using a maximum aperture value, it’s easier if you simply look at the chart photographs rather than read an explanation. Even a seasoned pro like Kazumi Takahashi—a photographer who has been staring through a viewfinder for over 10 years—was astonished at the level of resolution.
Initially, an image is composed by capturing through the lens wavelengths of light ranging from high to low—in other words, a wide range of frequencies. For example, if you are shooting a building, detailed workmanship and patterns are represented by high frequencies, while plain walls are conveyed in low frequencies; each has a role. To capture the highs and lows of these frequencies in a balanced manner and to meet the needs of the 4K era, development of the ZK Series involved accurately quantifying these frequencies and re-validating them from scratch. Plus, knowledge gained in the development of cine lenses—in a joint effort carried out with the ARRI Group—has been liberally applied. The result is an overwhelming level of sharpness across the entire zoom range, which is clearly evident even at a glance.
The next area investigated by Ellroy was distortion, a quality issue said to be inherent in zoom lenses. This comparison involved shooting a grid comprising a combination of simple, uniform vertical and horizontal lines. The test is based on the idea that any discrepancy in performance will be readily apparent, even at a glance. For the comparison group, they prepared a variety of lenses selected from a series of PL-mount prime lenses, beginning with a 14-mm wide-angle lens. Thorough verification tests were carried out by doing shoots using the ZK2.5 × 14 (14–35 mm) and ZK4.7 × 19 (19–90 mm) lenses with different combinations of focal length and T-numbers.
The results show that the ZK Series lenses performed very strongly in comparison to lenses that could be considered benchmark prime lenses. At the 14 mm wide-angle setting, where peripheral distortion is most likely to occur, slight distortion can be seen in all of the lenses. But as the focal length is gradually extended to 24 mm and 32 mm (ZK4.7 × 19), performance of the two different lenses was virtually identical to that of the prime lens. For the ZK Series zoom lenses, such a result is quite remarkable.
For a start, the number of lens elements that make up a zoom lens is extremely large compared to a single-focus prime lens. The developers explained that the ZK Series is composed of around 30 lens elements and that correcting distortion for all of these elements is extremely difficult. They noted that a large-diameter aspherical lens served to prevent distortion from occurring. Thanks to its long-term involvement in making broadcast TV lenses, Fujinon has accumulated a wealth of know-how in this area; for example, they successfully mounted the world’s first 30 mm or larger large-diameter aspherical lenses. Fujinon harnessed its technical capabilities and applied them to the development of cine lenses. They fine-tuned the composition ratio of low-dispersion glass and high-refractive index glass—two materials with different light dispersion properties. This intense dedication to the task resulted not only in low distortion, but also in high levels of contrast and 4K resolution.
There are many reasons for choosing a single-focus prime lens when shooting movies and advertisements. The main advantage is most likely that such lenses take interesting, nuanced pictures—images that please the eye in terms of color, contrast, blur quality, and so on. Could the ZK Series meet the needs of photographers in this respect? The color verification test involved live models and actual advertising shoots. The most important characteristic of color is how realistically it conveys the attractiveness of a subject. This is clearly evident in the skin tones and hair color of live models. And everything seemed to create an extremely natural impression, including the sharpness and accuracy of the contrast between bright and dark areas—for example, shadows of people or buildings—and a rounded, softly blurred quality in other areas.
As we saw above, ZK Series lenses incorporate about 30 lens elements. The Fujinon developers say that each lens element was fabricated after first reviewing the glass materials from which the element is made. The aim was, of course, to achieve the quality of a single-focus prime lens. Fujinon experimented with all sorts of combinations of glass materials, and further, with special coatings on filters, and the like. They continuously modified technologies for adjusting contrast and eliminating flare. Thanks to their painstaking efforts, the resulting image quality and finish is uniform across the four models of the ZK Series. The same goes for the HK Series, Fujinon’s lineup of high-end cine zoom lenses, and the Alura Series of cine lenses jointly developed with the ARRI Group. The ease of color grading is another area where these lenses will receive acclaim.
Fujinon's commitment to quality can be seen in the nine-blade aperture diaphragm the company introduced in the ZK Series. This design emerged from a wide range of simulations of aperture configurations. It captures light in a beautiful circular shape in all scenes, whether the aperture is at its widest or narrowest setting. And when it comes to crepuscular rays (“sun rays”), the nine-blade diaphragm draws out beautiful rays without excessive glare. Of course, full 4K support is possible with a compatible sensor size of Super 35 or greater. The ZK Series makes sense as a family of lenses that enable rich image expression that goes beyond the scope of existing zoom lenses.
Image quality and flexibility in the same class as prime lenses—a nice surprise!
In using the ZK Series, what I found most surprising was the high level of resolution. Even when comparing the center of the image, these lenses were in no way inferior to the single-focus cine lenses that were prepared for the verification tests—and this was clearly evident even up to the maximum angle of view. I therefore believe the ZK Series offers great advantages for shooting distant views of mountains and nature, say, or when shooting real estate and buildings with elaborate designs. And no matter what the scene, thanks to the superb sharpness, it was very easy to bring the camera into focus. This helps the shoot go smoothly, and it’s something I really appreciated. At this level of resolution, I can imagine that even editing tasks such as enlarging and trimming 4K images would be much easier.
When you’re shooting on location, time is of the essence. One of the major advantages of the ZK lenses is that you only need to tweak the zoom slightly when you want to adjust the angle of view. When we were on location for an actual ad shoot, I realized how totally efficient they are when used with equipment such as round mounting rails and cranes and the MōVI, a 3-axis gimbal stabilizer that’s being used more often these days. With round rails, once you’ve decided the focal length, it’s hard to change the setup; and when the sweet spot is midway between 24 mm and 32 mm, a zoom lens is a lifesaver. With the 3-axis gimbal stabilizer, adjusting the balance is quite tough, and a single ZK lens was a big help in enabling us to keep going without having to repeatedly swap single-focus prime lenses. And because the drive unit can be operated via remote control, you can freely attach and detach it. It’s nice to be able to use it flexibly as the situation demands. With the drive unit removed, the lens itself is about 500 g lighter. That made it much easier to work with, even when balancing it on the 3-axis gimbal stabilizer. In the past, we had to bring a zoom lens as well as a set of prime lenses to these kinds of shoots. But now, I can say without exaggerating that I’d gladly go with just the three ZK lenses.
The evolution of cine zoom lenses has been truly astounding. But if the technology is going to improve in the future, I’d like to see more focus on measures to counter distortion. Even now, I think that the correction is working well enough, but I’ve heard from our in-house editors that it’s still a bit of a hassle to correct distortion. It’d be ideal if post-processing could go as smoothly as shooting on location.
Cine zoom lenses = an assembly of prime lenses The greatest value that ZK Series offers
The ZK Series has completely changed how we think about zoom lenses, thanks to the results of these verification tests over a wide range of parameters. Compared to prime lenses, these lenses provide such a high level of image quality—beginning with resolution—that it’s hard to say which type is better. Depending on the situation, the ZK Series is sometimes even superior. The ZK Series can also reduce the time and effort that would normally be involved in swapping prime lenses. In other words, they are high-performance lenses that provide the value of four or five prime lenses.
Commitment and passion with regard to creating images... Higher on-location efficiency... The ability to achieve both is a major bonus on the directing side. Using the ZK Series enables directors to satisfy a wide range of requirements—for example, when shooting time on location is limited, when you want to finish shooting before models lose their concentration, when you want to capture a creative image inspired by the location, and so on.
One more thing: Ellroy also experimented with shooting 6K HD, and they want to state for the record that there was almost no vignetting. Ellroy offers a 6K shooting and editing service, but there are still only a few cine lenses compatible with the size of the 6K sensor in the Red Epic Dragon camera, and the image circle remains a bit of a headache. In fact, vignetting could be seen somewhat on the periphery, even in the prime lenses used for the comparison. Being able to eliminate vignetting alone makes the ZK Series a worthy new product. It’s no exaggeration to say that the ZK Series has the potential to radically change how shooting is done in the 4K era.