Sony a7S Full-Frame Mirrorless Camera, Part 2: Adapting Lenses to the E-Mount

Sony E-Mount

The advantages of using an E-mount lens on an E-mount camera are that the lens communicates directly with the body and the two were designed to work together. In addition to being the only lens combination that works to add stabilization via Sony’s Optical Steady Shot, using a Sony E-mount lens on an E-mount camera adds two important features that you can’t get using third-party lenses and mounts

Sony E-mount lenses use an electronic iris instead of a mechanical one. The big advantage of an electronic iris is that on a lens that would ramp down on a mechanical lens when you zoom in, it's possible for the iris to hold an F-stop through the entire zoom range if you first stop it down. This is an iris behavior unique to Sony E-mount lenses and I was first tipped off to this feature on the Sony 18-200mm f/3.5-6.3 E-mount lens. You zoom the lens out to 18mm, then you close the iris down to f/6.3, and when you zoom through the range instead of it continuing to stop down even further, it actually opens the iris to compensate and maintain the light transmission levels at f/6.3.

Unfortunately, in order to take advantage of this electronic iris zoom ramp compensation feature, you first have to stop down your lenses and this means you need to film at a higher ISO. In the past, this was a small issue for the Super35mm sensor FS100 and FS700/Rs but it isn’t as much an issue on the α7S because if its even lower noise and high ISO capabilities.

Sony E-mount lenses on the α7S can also take advantage of lens correction to compensate for light fall-off, geometric distortion, and chromatic aberration in video mode. Keep this in mind when reading E-mount lens reviews, as they normally turn off these corrections for testing purposes. Although if you are using E-mount lenses on cameras that do not currently support lens correction, like the Sony FS100 and FS700/R, then light fall-off, geometric distortion, and chromatic aberration matter in your lenses. In April at NAB 2014, Sony announced that it does plan on releasing a firmware update to add lens correction to the FS700 this year, but calls to Sony for additional details on this have been unreturned at this time.

In-camera lens corrections are more important for E-mount lenses than possibly for any other camera-and-lens system because Sony is producing their new E-mount lenses knowing that they don’t need to be perfect in these three aspects, and can focus their optics knowledge and lens value on features like sharpness, size, weight, and power zoom. Normally there is a trade-off in balancing all of these needs within a price range; Sony is smart to prioritize optical features with workflow considerations in mind.

One example of a great and inexpensive video lens is the Sony PZ 18-105 f/4 G OSS Power Zoom lens that sells for only $600. It covers an impressive 5.8x zoom range, maintains a constant aperture through this range, and is parfocal. Without in-camera lens corrections you wouldn’t want to use this lens on your camera, and I don’t on my FS700 for this reason, but if you only buy one zoom lens for use on the Sony α7S, this is the one I would recommend.

Sony 16-50mm f/2.8 A-mount lens with LA-EA2 adapter, Sony 10-18mm f/4 e-mount lens, Sony 18-105mm f/4 lens, and Rokinon 24mm t/1.5 lens.

I have also picked up the Sony 10-18mm f/4 OSS lens for my Sony α7S. It was designed for APS-C sensors, so when you use it in APS-C mode you have to factor in a 35mm equivalent range of 15-27mm. This is plenty wide, but if you still need a wider lens, you can actually use the Sony 10-18mm f/4 lens on the full frame sensor starting at 11mm focal length, if you don’t mind some corner shading or vignetting. You simply have to remove the lens hood first because it will enter your frame as it wasn’t designed to be used on a full frame sensor.

In my own workflows, I find that the focal range I'm missing most from my current lens lineup is a single lens that can cover the 35-105mm range on a Super35mm sensor with a 1.5x crop factor. I don’t plan on using the Sony α7S for long-lens work as much as for a handheld camera to take the place of my Canon XA20 camcorder but it just might see some long lens action if Sony doesn’t add in-camera lens correction to the FS700 or the FS100 entirely.