4-5 stop difference between HPX250 & HMC40

[Berk]

Hi
we are planing to use HMC40 as Bcam in our production. Our initial test showed us there 4-5 stops difference between HPX and HMC 40. We set both cam 1080p 30p 1/60th. When the zebras at %70 to get one bar on the face we adjust the iris of HPX at f5.8, HMC40's full open.

I know HMC has digital automatic ND. so that can't be on.
Might something we are overlooking?

[Barry_Green]

Hmc40 is 50 iso. The hpx250 in PAP2 is 640 iso. That's three and a half stops different.

You said your shutter on the 250 was 1/60th; it may not have been. On all other Panasonic handhelds, "shutter off" is 1/50th in 30p, but on the hpx250 "shutter off" is 1/30th. So that would be about 2/3 of a stop more.

Then, you said the hmc40 was "open" but open doesn't tell you the f stop. It depends on how far you were zoomed in. What is the next f-stop reading right before "open"?

The hmc40's ND filter is not electronic or digital. It is a physical filter that slides into place gradually as needed. It will never be used at any iris more open than f/2.8, IIRC.

[Berk]

Thanks Barry
For our test both cameras are zoomed out all the way. HPX was in 30PN mode and shutter was 1/60th same with HMC (30p mode, shutter 1/60th). I think native Isos of the cameras explain the difference.