When High Definition TVs were announced years ago, 1080i was the highest resolution in the array of available formats. No one (at least consumers) dreamed that this was just the starting point.
Secrets of Home Theater and High Fidelity - John E. Johnson, Jr.

The progressive format 1080p (let’s call it 2K for the 1,920 pixels) replaced 1080i, and 4K (4,096 x 2,160 for commercial theaters, and 3,840 X 2,160 – Ultra HD – for consumers home theaters) seemed to appear out of nowhere and ended up on Costco’s front show cases in short time. It has been announced that the Tokyo 2020 Olypmpics will be broadcast in 8K, along with NFL football games.

Camera sensors have grown in pixel count, such that medium format digital cameras have 50 megapixels, full sized DSLR cameras have 36 megapixels, and compact digital mirrorless cameras with interchangeable lenses have 24 megapixels (6,000 x 4,000). This is certainly enough pixels to handle 4K.

However, as the number of pixels in camera sensors has increased, the lenses have not changed, and in fact, at least one manufacturer is marketing a semi-pro 4K video camera with one of the lenses similar to the lens made for their compact mirrorless snapshot cameras. This is the Sony NEX-FS700R Super 35 Camcorder with 18-200mm f/3.5-6.3 PZ OSS Lens, at $5,600. This camera uses the E-Lens Mount, which is the same lens mount as their compact mirrorless cameras.

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This prompted me to analyze several lenses, one of which is a Sony 18-200mm f/3.5-6.3 ($900), which I obtained when I purchased a Sony NEX 5 camera (mirrorless compact camera). The 18-200mm lens is about $900. This lens was also offered on the Sony NEX-FS100UK Super 35 Camcorder (photo shown below), for shooting 1,920 x 1,080 (2K), but the camera is no longer available. The lens has manual zoom, and extends during zooming, while the version on the NEX-FS700R video camera has electronic zoom and moves its lens elements intermally when zooming. This lens is availble separately for about $1,200.

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I also now have several lenses with the E mount for the NEX 5 as well as the Sony Alpha 6000, which is the successor to the Sony NEX 7. The NEX 5 has 16.8 megapixels, and the Sony Alpha 6000 has 24.3 megapixels. A second lens that I have is a Sony 18-55mm f/3.5-5.6 ($300), and a Sony Vario-Tessar T E 16-70mm f/4 ($1,000). The Vario-Tessar was designed by Zeiss.

Lastly, I just purchased a Sony E PZ 18-105mm f/4 G OSS Lens, with electronic zoom, which looks very similar to the Sony 18-200mm f/3.5-6.3 PZ OSS electronic zoom lens on the video camera. The 18-105 also has lens elements that move internally during zooming.

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Here are two other lenses discussed in this article.

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All lens and camera photos © copyright Sony.

For the lens resolution analysis, I used Imatest software, available here. This software is becoming a standard in precise analysis of many lens parameters.

I set up my Alpha 6000 camera 8 feet from the test pattern, which was a black field adjacent to a white field on a computer screen. The two fields, side-by-side, took up the entire screen. I tilted the camera so that the test pattern was photographed at an angle (this is necessary to perform the resolution – sharpness test). I can’t create a tilted black and white pair of fields on the screen because it would produce a jagged edge, and a straight edge is necessary. The straight edge is produced by having the two fields straight up and down, and tilting the camera to produce the tilted image.

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I used the shortest focal length of each lens, at its largest f/stop and f/8. The jpg files generated by the camera and lens combination were then opened in Imatest and the FSR test was run, which generated a graph that showed the MTF-50 in Line Widths/Picture Height (LW/PH) and the chromatic aberration (CA).

MTF-50 represents 50% contrast. Shown below are two figures. The first one has alternating black and white lines at 100% contrast. Each line pair represents one cycle.

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This figure shows line pairs at 50% contrast. In the graphs, the MTF-50 score represents how many line widths (single lines, black or white) per picture height are resolved at 50% contrast. This is a standard for measuring lens resolution that has been accepted by the industry for evaluating digital image quality.

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So, let’s get started. The first figure is the stock lens that came with my original Sony NEX 5 camera, a Sony 18-55mm zoom lens (I use this lens with the Sony Alpha 6000 now).

This figure, taken at f/3.5, displays an MTF-50 of 3123 LW/PH (blue arrow). Since 4K is 3840 x 2160, the resolution (sharpness) is more than adequate (the 3123 number is the number of lines from top to bottom), and there are 2160 lines from top to bottom in a 4K video image). The Cycles/Pixel (Cy/Pxl) of 0.39 (blue arrow) is slightly below the minimum of 0.40 that is accepted as being sufficient. A Cy/Pxl of 0.5 would be perfect, i.e., 100% contrast.

Professional studio lenses are available for 4K cameras, at around $4,000 to $40,000. For example, a Canon EF Cinema Prime Lens Kit (three prime lenses at 24, 50, and 85mm) is $12,700. A Canon CN-E30-105mm T2.8 L S Telephoto Cinema Zoom Lens is $19,275. Fujinon sells their 19-90mm T2.9 Cabrio Premier PL Zoom Lens for $39,800. These lenses are all designed to be used with professional 4K cameras. One would certainly expect a Cy/Pxl very close to 0.5 not only at the center of the image, but at the periphery.

The Cy/Pxl refers to the definition of a cycle being one line pair, that is, one horizotal white line and its adjacent horizontal black line, with each line being one pixel in height. So, if the contrast is 100%, the Cy/Pxl would be 0.5, since each pixel is half of a cycle. Actually, the Cy/Pxl is the more important number to look at since there are so many differences in the megapixels in camera sensors. If one sensor has 12 megapixels and another has 24 megapixels, and they both test out at 0.45 Cy/Pxl, then they both are likely to have the same contrast capability.

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Chromatic abberation (CA) was 0.116 pixels (blue arrow), which is excellent. Chromatic aberration is the spreading of white light into its colors as it passes through the lens, so you end up seeing color at the edge of objects in the image. You can see the minor color (red, green, and blue lines) spread pointed out by the red arrow. Compare this spread in the other photos.

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Here are the graphs for the same lens, at f/8. The 0.426 Cy/Pxl result is really good.

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Chromatic aberration was slightly reduced, at 0.108 pixels.

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Moving on to another lens, the Sony Zeiss 16-70mm, first the MTF-50 plot at f/4. The MTF-50 was 3,841 LW/PH, with 0.435 CY/Pxl. This is a good result.

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However, the chromatic aberration was much higher than with the 18-55mm lens, at 0.599 pixels.

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Going to f/8, the LW/PH dropped to 3,166, with a 0.396 Cy/Pxl, so the performance was better with the lens wide open. This is unusual. For the most part, lenses perform better with the aperture stopped down 2 or 3 f/stops from the wide open aperture.

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Chromatic aberration at f/8 was 0.537 pixels.

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Here are the results for the Sony 18-200mm zoom lens (the same lens that comes with the Sony NEX-FS700R Super 35 Camcorder).

The MTF-50 at f/3.5 plot showed 0.425 Cy/Pxl and 3,400 LW/PH.

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Chromatic aberration was 1.02 pixels.

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And at f/8, the LW/PH was reduced from what it was at f/3.5. The Cy/Pxl was 0.408, also a reduction (worse performance).

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Chromatic aberration was also reduced a bit from what it was at f/3.5, which is what we would expect (better performance).

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I also measured the MTF-50 at the periphery of the visual field for this lens (18-200mm), i.e., the top left corner. All lenses have lower performance at the edges.

At f/3.5, the MTF-50 is 2108 LW/PH, with a 0.264 Cy/Pxl. Obviously, this is not going to maximize the imaging capability of a 4K sensor.

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Chromatic aberration was 1.57 pixels.

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At f/8, the LW/PH was almost as good as at the center of the lens. So, stopping this lens down to f/8 would deliver a much better image. The Cy/Pxl nevertheless was below 0.4.

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Chromatic aberration, however, was worse at f/8 (1.71 pixels) than it was at f/3.5.

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Let’s now take a look at the newest lens, the Sony E PZ 18-105mm f/4 G OSS.

At f/4, center field, the MTF-50 was 2,363 LW/PH, almost identical to the 18-200mm lens.

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Chromatic aberration was 1.7 pixels, worse than the 18-200mm lens.

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At f/8, things improved. The MTF-50 was 2,950 LW/PH.

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Chromatic aberration also improved, at 1.19 pixels.

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When the test chart was at the top left portion of the image field, and a f/4 aperture, the resolution was slightly improved, at 2,404 LW/PH, which is a bit unusual.

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Chromatic aberration was reduced by more than 50%, to 0.483 pixels. Very unusual.

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Changing the aperture to f/8 gave the following results.

The MTF-50 was 2,952, essentially the same as it was in the center of the image, which is, again, not usually seen.

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Chromatic aberration was 0.673 pixels, slightly worse than the center field, and this would be expected.

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The results of this study show that moving on from 2K to 4K doesn’t mean that you can use the same lenses that were designed for 2K or for snapshot cameras that have a high megapixel count. Sensors with a 4K megapixel arrangement (8.3 megapixels) would be easy to make, but the lens is another story.

The lenses tested in this article do not perform as well as I had anticipated, and they could be used with 4K video cameras. I am certain that this performance is not confined to Sony. Manufacturers are going to need to retool their lens production so that we get sharp images both at the center and periphery, with low chromatic aberration. Otherwise, the picture quality with the old lenses will not produce as high a quality image on the 4K Ultra-HD TVs that are now being sold at stores, and which are apparently being purchased by a lot of consumers, being shown that the 4K TV is only a couple of hundred dollars more expensive than the 2K HDTV of the same size.

I used my own Sony camera and lenses for this article because I have a complete set. It’s my photographic system. The lenses are in the same price range as lenses for standard sized DSLRs, so I would expect them to perform at high quality. However, the results of my tests here are all over the map, suggesting that the lenses are sourced from several different companies in China. Sony needs to do better at QC (qualith control) and put some effort into designing better lenses, especially because there is a trend for photographers to set aside their full sized DSLRs in favor of these much more compact cameras with APS-C sensors (about 37% less area than the 35mm full size sensor in large DSLRs). That is exactly what I did, selling my full sized DSLR and set of lenses in favor of the Sony compact system. My best friend did the same thing. So did my Dermatologist. So, that’s myself and two people I know who have dumped their large DSLRs and bought compact mirrorless cameras with interchangeable lenses. To the manufacturers of these compact cameras, I ask you to please make better quality lenses.

Consumer 4K video cameras are now available in the $1,000 to $2,000 range. One can only imagine the quality of the lens in such cameras. I hope to get my hands on some of these to test. And for the Indie film-maker, I suggest renting the good lenses rather than purchasing the inexpensive ones.

John E. Johnson, Jr.

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