How to Emulate Super 35mm 4K Video with the Panasonic GH4

The Panasonic GH4’s ability to record both DCI 4K and UHD video internally, without line-skipping or pixel binning, sets a new standard for in-camera video recording with HDSLR and mirrorless cameras. However, a potential drawback of this method is that the GH4 can only use the center portion of the sensor. This results in about a 2.3x crop factor when compared to full-frame cameras, as opposed to the typical 2x crop for normal Micro Four Thirds cameras, which puts the GH4 into slightly weird territory when it comes to using lenses. It¡¯s smaller than normal Micro Four Thirds and larger than super 16mm, making native lenses hard to find. Luckily, there is one combination that ends up working really well: using APS-C or DX-optimized lenses with a Metabones Micro Four Thirds Speedbooster.
Update: A chart has been added at the end that compares the effective focal length of these lenses with a Speedbooster, to their 35mm equivalent focal length¡ªtaking into account the 4K crop you get with the GH4, and the changes in specs introduced with use of a Speedbooster.

“One combination that ends up working really well: using APS-C or DX-optimized lenses with a Metabones Micro Four Thirds Speedbooster.”

Normally, when you mount a lens designed for a larger sensor on a camera with a smaller sensor, all of the light that doesn¡¯t hit the sensor is unused. However, the Metabones Speedbooster concentrates the light entering the lens into a smaller area, which virtually decreases the focal length and increases the aperture on the smaller sensor. The Nikon G to Micro Four Thirds Speedbooster reduces the focal length of the lens and the lens circle area by a factor of .71, which also increases the apparent aperture by one stop. For the typical Micro Four Thirds camera with a 2x crop factor, a .71x reduction reduces the image circle to a slightly smaller area then APS-C optimized lenses are designed for, effectively a 1.42x crop factor, while APS-C lenses are designed for a 1.5x crop factor. Some lenses may work, but others may present a little vignetting. However, when shooting 4K video on the GH4, it works out nearly perfectly. The field of view will be almost identical to having an APS-C camera, as the overall crop factor with the Speedbooster while shooting 4K with the GH4 is about a 1.6x, nearly identical to APS-C still or Super 35mm cinema cameras. At this time, there is only a Nikon to Micro Four Thirds version of the Speedbooster available, so this article will focus on lenses that are available for Nikon Cameras.
Below is a list of APS-C optimized lenses that will make a great option for shooting 4K video with the Panasonic GH4, when paired with the Metabones Speedbooster.
Wide-Angle Lenses
Shooting wide is one of the more difficult aspects of dealing with crop factors that lack native lenses. The widest-angle lens available natively for Micro Four Thirds is a 7-14mm f/4 lens from Panasonic. With a 2.3x crop factor, that lens works out to be 16.1mm-32mm, which is still respectively wide. However, if you go the route of adapting wide-angle, APS-C-optimized glass paired with a Speedbooster, you can go ever wider, or get a similarly wide angle of view at a much faster aperture.

Tokina 11-16mm f/2.8
When paired with the Speedbooster, a Tokina 11-16mm f/2.8 becomes an effective 7.8-11.4mm lens with a constant f/2 aperture. While not quite as wide as the native Panasonic 7-14mm, the extra two stops could definitely come in handy. The 35mm equivalent field of view of this lens when shooting 4K video on the GH4 would be approximately 18mm-26mm.

Sigma 8-16mm f/4.5-5.6
For those wanting to go as wide as possible on a rectangular lens, the Sigma 8-16mm will fill the bill. When paired with the Speedbooster, this lens becomes an effective 5.7-11.4mm, with approximately an f/3.2-4 aperture. The 35mm equivalent focal length, when shooting with a 2.3 crop factor for this lens, works out to 13.1mm-26mm, which should be wide enough to please any wide-angle enthusiast. This lens will almost certainly vignette slightly when used with the standard Micro Four Thirds 2x crop factor.

Samyang 10mm f/2.8
The new Samyang 10mm f/2.8 lens is a relatively fast manual focus prime lens optimized for APS-C cameras. It’s resold under a few different brand names, including Rokinon and Samyang. Paired with the Speedbooster, this lens becomes an effective 7.1mm f/2 lens, a full 2 stops faster than the 7-14mm Panasonic, with just as wide of a field of view. The 35mm equivalent of this lens with the Speedbooster works out to approximately 16.3mm. While this lens is available with a Micro Four Thirds mount, using the Nikon mount version allows you an extra stop, and a wider angle of view, when you want it.

Fast 50mm
Another popular lens segment is the fast 50mm lens. Micro Four Thirds has a number of fast 50mm equivalent lenses, like the Voigtlander 25mm f/.95 and the Panasonic 25mm f/1.4. But going the route of a Speedbooster and adapted glass can give you similar results at a lower price. Here are a few APS-C prime lenses that could fill this gap.

Nikon 35mm f/1.8
The Nikon 35mm f/1.8 is a relatively affordable lens that’s designed for its DX (APS-C) series DSLR cameras. Paired with a Speedbooster, it becomes approximately a 25mm f/1.2 lens that will give you around a 57mm (35mm equivalent field of view) when shooting 4K video with the GH4.

Sigma 30mm f/1.4
The Sigma 30mm f/1.4 is a little wider and a little faster than the Nikon 35mm 1.8. With the Speedbooster, this lens becomes an effective 21mm f/1.0 lens for Micro Four Thirds. The 35mm equivalent field of view?is 49mm. This lens is a great option for those looking for the closest to a 50mm field of view when shooting with the 2.3x crop mode on the GH4, as even the native 25mm lenses will offer a field of view closer to 60mm.

Constant Aperture Zoom Lenses
When shooting video with a zoom lens, it’s important to have a constant aperture to avoid the abrupt exposure changes that are common with variable aperture still lenses. Luckily, there are a number of high-performing APS-C constant aperture zoom lenses available from a number of manufacturers, for a lot less expense than the few constant aperture zoom lenses available for Micro Four Thirds.
Sigma 18-35mm f/1.8
The Sigma 18-35mm f/1.8 is a pretty groundbreaking lens for APS-C cameras. Offering an aperture typically reserved only for prime lenses on a constant aperture zoom, predictably, turned a few heads. When paired with the Speedbooster, this lens becomes an impressive 12.8-25mm f/1.2 effective lens, which is faster than most primes available for Micro Four Thirds, with the convenience of a zoom lens.

Tamron SP AF 17-50mm f/2.8
For those needing a little more zoom range than the Sigma 18-35mm offers, who aren’t hampered by a mere f/2 effective aperture, the Tamron SP AF 17-50mm f/2.8 is a great option. Paired with the Speedbooster, it’s like a using a 12-36mm f/2 on the GH4 when shooting 4K video. Its flexible range is great for handheld shooting.

Sigma 50-150mm f/2.8 OS
The Sigma 50-150mm f/2.8 is an APS-C replacement for full frame 70-200mm lenses. Paired with a Speedbooster, it becomes an effective 36-107mm f/2 constant aperture lens. This is a great medium-telephoto zoom lens option for the GH4. The current version of the lens also offers Optical Image Stabilization; however, since the Metabones Speedbooster does not provide power to the lens, users will not benefit from it. It might be worth looking for the older, non-OS version of this lens, which can be found for at a more affordable price in the used market.

These are just few of the many great lens options for the GH4, as the Micro Four Thirds lens mount is extremely adaptable. Hopefully, some of these suggestions will get you get started if you decide to use a Speedbooster.

Effective Focal Length with Speedbooster
35mm Equivalent Focal Length with the 4K Crop & Speedbooster

Tokina 11-16mm f/2.8
7.8-11.4mm f/2?

Sigma 8-16mm f/4.5-5.6?

Samyang 10mm f/2.8?
7.1mm f/2?

Nikon 35mm f/1.8
25mm f/1.2?

Sigma 30mm f/1.4?
21mm f/1.0?

Sigma 18-35mm f/1.8
12.8-25mm f/1.2?

Tamron SP AF 17-50mm f/2.8?
12-36mm f/2?

Sigma 50-150mm f/2.8 OS?
36-107mm f/2?