8mm Sigma fisheye/exposure

[Reg Wiest]

Just picked up a used 8mm Sigma F4 fisheye. 
I suspect that because a circular image is produced in the middle of the neg
and no light reaches the edges of the neg, I must deviate from in-camera
light meter readings (using LX, ME Super, MZ5-N)??? Perhaps, the best bet is
to shoot a roll of film and bracket the exposures to determine how much
compensation is required . . . or use a hand-held light meter.
RW