|Hi Gautham, as you known the barrel distortion generally occur with wide angel prime lenses based on their structural features or if any fisheye attachment was used with such lenses. Exposure compensation is needed, but it is built into the lens mount. The aperture of the lens is left wide open throughout. A ring on the attachment is set to correspond with the focal lenght of the lens; then secondary aperture in the fisheye attachment lens mount is used to control the exposure. Very ingenious indeed. But this situation stemning only my angular POV and selection of a relatively shallow DOF MF! Absolutely intentional!
Have a nice day!
Meleagerís Blue (Male) (63) *