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GH4 Lens Translation
  • thebmillzthebmillz

    Hi all!

    My apologies for the dumb question in advance.

    I was lucky enough to be shooting a film on the Arri Alexa and our go to lens started to become a 40mm.

    I just upgraded my GH2 to a GH4 and I was curious what lens would equal a 40mm.

    Right now I own:

    • SLR Magic 12mm
    • SLR Magic 25mm
    • Noctitron 42.5mm

    I assumed something like a 16mm would get me close to a 40mm? But, I'm not sure about the math here. I was under the impression with the GH2 it was roughly double. So, a 25mm on a GH2 = a 50mm in the 35mm film world. But, I'm pretty sure the GH4 has a different crop.

    Thanks!

  • 3 Replies sorted by
  • Rivo_KikkulRivo_Kikkul

    It is still roughly 2x (in 4k mode a bit larger crop). So 20mm Lumix will be 40mm.

  • joetheprojoethepro

    Alexa crop factor * 40mm = GH4 crop factor * (focal length you need)

    So... Focal length you need = (Alexa crop factor * 40) / GH4 crop factor.

    Cmon now, use that brain. :)

  • RyLoRyLo

    GH2 is roughly double relative to full frame 35mm (for photos). The Arri Alexa is a Super 35mm camera (well, it's close). This means, compared to full frame, it's cropped, too. The Arri's crop factor is 1.5x, relative to full frame. So relative to full frame, the GH4's crop factor in Cinema 4K mode is somewhere around 2.3x. Relative the Arri, it's 1.55x.

    That's just so you understand the next part, which is all you need to remember. Using joethepro's formula above, to get the equivalent field of view of 40mm, you need a 26mm lens. If you need to figure out the same for any more lenses, just divide by 1.55 or multiply by .65. Whichever is easiest for you to remember.

    Also, using a speedbooster with the GH4 will get you close at around the same focal length (1.1 crop relative to the Arri). 35mm + speedbooster will match 40mm.

    I hope that helps!

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