Sony a7S Full-Frame Mirrorless Camera, Part 1: Lens Options

Sony does have some experience with the 28-135mm range via the old Minolta 28-135 F/4-4.5 lens that was nicknamed “the secret handshake” and is regarded as an exceptionally sharp lens. If you believe stories in online forums, the secret handshake got its name because it was deemed to be far superior to its selling price, was sold at or below cost, and was a thank you to loyal Minolta customers. I once tested the secret handshake lens but found it wasn’t parfocal and have no idea if any of that old Minolta magic will make its way into Sony’s new lens or if it is an entirely new design, but I would bet the new 28-135mm F/4 lens will be parfocal as many of Sony’s newer lenses are. It would also be nice if Sony decided to sell this lens at or below cost too but I doubt that will happen. When I did ask Sony about a price range I was only told that they are aware of the market it is being designed to be sold to and would have to keep the pricing affordable. I take this to mean much less than say a $25,000 Canon 35-105mm T2.8 Cine-Zoom lens.

Filter Ring Rotation, Extension, and Diameter

If you are planning on pairing your camera with a matte box, lens support, and/or polarizer filter then you will care if your lens rotates or extends when you focus or change focal length. Otherwise an internal zoom and non-rotating filter isn’t as important to you. I should also note that if you plan on using a matte box then you may also want to avoid a lens with a focus ring that is too close to the front of the lens barrel as it might not be accessible with the matte box. Filter diameter matters when you want to share filters across several lenses and larger filters do cost more than small ones and are indicative of a heavier lens but on the plus side, they do look more impressive and professional.

I never used to worry about lens size for use on my FS100 & FS700 video cameras because they were only ever operated on tripods and sliders but for use on my α7S, I’m finding size does matter and for casual shooting my Minota 28mm f/2.0 Rokkor-X lens sees more action than do my larger lenses.

Smart on IQ

Lens image quality, often referred to as IQ, covers more than just resolving power. Photographers place a large emphasis on lens resolving power and if I was taking photos on a 36MP sensor, I would too, but even 4K video is just over 8MP and the Sony α7S sensor is a native 12.2MP sensor in 3:2 photo mode and less in 16x9 video mode, so I am going to argue that peak resolving power isn’t terribly important for video work.

It is important, however, to understand that lenses typically have higher resolving power at the center of the lens and a lower resolving power towards the corners. The same goes for light fall-off, which is more pronounced at the corners. The results of lower corner resolving power and light fall-off are some corner softness and corner shading. This is especially true when using full frame lenses on a full frame sensor like on the Sony α7S, and less on APS-C or Super35mm sensors that use more of the sweat spot of a full frame lens. The same corner issues can appear if you are using lenses designed for smaller APS-C sensors on an APS-C or Super35mm sensor but likely to a lesser degree.

Less Perfection, Please

Having as close to a theoretically perfect IQ isn’t always desired. Often times when videographers refer to a lens having character they are referring to a combination of IQ deficiencies that help achieve a certain look in-camera, like a natural lens flare and corner shading. The same theories applies for film makers who want to add digital film grain to a perfectly clean image, although I never appreciate those effects except in flashback scenes.

Sometimes too much lens character can be a bad thing too and I had to sell my old Angenieux designed Tokina 28-70mm f/2.6-2.8 because it flared and ghosted too much, which was risky when I couldn’t control available light sources. The same can be said for lenses that exhibit too much coma or busy bokeh.

More Perfection, Please

Along with light fall-off, chromatic aberrations (CA) and geometric distortion are lens characteristics that some camera and lens pairings can correct in-camera or that photographers commonly correct with software like Adobe Lightroom. CA typically shows itself with purple fringes on edges and like most image quality deficiencies, is more obvious the more open your iris is. Geometric distortion is more pronounced at the corners of the frame and causes straight lines to bend undesirably.

The Sony α7S features in-camera lens compensation to correct for Corner Shading, Chromatic Aberrations, and Geometric Distortion.

Unfortunately at the time of this writing, no video editing NLEs offer lens and camera specific CA, distortion, and light fall-off correction so these IQ issues can be real concerns that affect videographers more than photographers, who have more options to correct them. While correcting for IQ issues is not new for photography, it is in videography and the Sony α7S is one of the first cameras that support lens corrections in-camera in video mode. Of course you need to pair it with a Sony E-mount lens first to enable this in-camera function but this one feature has turned the otherwise unusable, because of its awful pincushion distortion, Sony 18-105 f/4 G OSS Powerzoom lens, into a great video lens, albeit a crop sensor one that doesn’t fully take advantage of the full frame Sony α7S sensor.

The Sony α7S with Distortion turned-off showing undesirable lens curvature on the Sony 16-50mm f/2.8 α-mount lens. You cannot turn off distortion correction on E-mount lenses.

Constant Aperture

Videographers care more about a lens that has a constant aperture through its entire zoom range because if your lens ramps down and closes its iris the more you zoom, this will impact your exposure and you will have to adjust your ISO to compensate. ISO and GAIN are the same thing but in different units of measurement. If you compare the $499.99 Sony FE 28-70mm F/3.5-5.6 OSS lens to the $1,199.99 Sony Zeiss Vario-Tessar T* 24-70 F4 ZA OSS lens you might be tempted to choose the less expensive model which is a bit faster wide and a bit slower at telephoto, but this would be a mistake. The difference between f/3.5 and f/5.6 is two full stops, which is a 4x difference in light transmission. This might be ok if you can stop recording, change your ISO, and carry on, but if you need to zoom while filming you want a constant aperture lens.

In part two in this series I will reveal a workaround that will enable E-mount lenses to maintain a constant aperture even if the lens isn’t rated for such and I will discuss lens and mount combinations for the Sony α7S from a videographer’s perspective.