They arrived today. Must say, i am Impressed. not only by how bright that Flash actually is, but also that this made an even bigger mess than i expected. Also How damn Light Sensitive those Phantoms must be, to capture that this well at those framerates. But also shows, why they probably cost so insanely much.
Like i guessed 1000fps is no problem, and up to 2100 is still looking ok, up to 3500 fps is possible, but looks fairly bad, above that you will really have Trouble seeing that Flash well through all the Noise, have not even tried anything above 6000fps. On my 2.1 that is, cant speak for an 1.4, and i have no idea how Sensitivity of the Two compares.
I gave it about any chance i could, Shooting with an 0,58x Metabones and an 50mm 1.4 Lens for an Effective Aperture of f/0,812 (=T/0,87) and with the IR-Filter Removed, to even capture that little bit more Light that would eat.
Shot at 2142fps at 6dB analog Gain and 12 or 18 dB Digital Gain, 354° Shutter. Obviously a ton of Motion blur because of that, but cant do much about that for Such Low-Light Shots that are just barely possible anyways.
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Regards your f/1.3 Prime Lens, you can try, but it was challenging at f/0.8 already, which is almost two full stops of Light more than your Lens, so dont expect anything close to those Phantom-Shots if you use that lens.
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#EDIT:
Forgot to add, this was shot on 5.1 Unstable Firmware also, to just get a brighter Image. Obviously more noise, but a bit Brighter than 6.0 at least, havent done a ton of testing still with 7.0.
/EDIT#