Aperture Width and VrayPhysicalCamera

[GLASS-CANVAS]

I've got a technical question about how cameras work in Max and VRay, most likely for Vlado to answer:

Starting in the Max render dialog just above the resolution buttons is a box marked 'Aperture Width(mm)' which defaults to 36.0

Moving on to a VRayPhysicalCamera the first dialog is 'film gate (mm)', which also defaults to 36.0

My question is this: If I want to do a camera match with a full-frame Nikon D800 what do I set these values to? Back in the Max Render dialog there is a pull-down preset called '35mm (24mm x 36mm) (slide)' which I assume tallys with the sensor on my Nikon. When I choose this preset the Aperture Width(mm) dialog chages from 36.0 to 34.2. Does this mean I need to change the VRayPhysicalCamera dialog 'film gate (mm)' to 34.2 as well?

It's damn confusing! Any help would be gratefully received.

[vlado]

The physical camera ignores the Aperture value in the Render dialog. So you have to adjust the value there separately.

Best regards,
Vlado

[GLASS-CANVAS]

Thanks for the clarification Vlado.
I have done some poking around and discovered that the film gate of a full frame DSLR, such as my D800, is indeed 36.0 and not 34.2 as Max suggests. I have no idea where the 34.2 value comes from.