Metabones introduces Speed Booster XL 0.64x for Panasonic GH4: Digital Photography Review
BMCC variant Speed Booster works on GH3 and GH4 to give 1.28x crop, near full frame - EOSHD.com - Filmmaking Gear and Camera Reviews
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Panasonic GH4 Review - 4K video for filmmakers
Hands on with the new Metabones Speed Booster Ultra - fast AF with Canon lenses on Micro Four Thirds - EOSHD.com - Filmmaking Gear and Camera Reviews
Canon Lenses On The Panasonic GH4, Using The Metabones Speedbooster Adapter | Fstoppers
VILTROX EF-M2II 0.71x Speed-booster Adattatore MFT per Obiettivo EF mount a Micro 4/3 Fotocamere GH6 GH5M2 BMPCC 4K GH4 GH5 G100 G95 G85 OM-1 EM-1 : Amazon.it: Elettronica
Viltrox NF-M43X Focale Riduttore di Velocità Adattatore Booster Turbo w/Apertura per Nikon Lens per M4/3 della macchina fotografica GH4 GH5GK GH85GK GF7GK GX7 - AliExpress