The ExpoDisc (4x5.65") lens mount_Praktica Electronic something else

something else

but several other bodies including the F4 and F/N90 work as well

but a solid user

some leatherette shrinking

with a 28mm-ish field of view and just a happy bit of distortion

The ExpoDisc (4x5.65") lens mount_Praktica Electronic something elseThis particular Expodisc is not a disc it's a big 4x5. 65" slab designed to slip into matteboxes but it works the same as the classic. Basically, it's a specialized flat diffuser designed to facilitate setting custom white balance. Rather than hauling around a gray card, or trying to find a plain white surface, or hoping that your camera guesses correctly, you can toss this in front of your lens and lock in an accurate custom white balance in seconds.