I am seeking comments/corrections to my lens logic below. I have APS-C camera (1.5x) and 18-250mm lens. For the purposes of this scenario, my subject is stationary, so image stitching is possible. If I buy a 10mm UWA lens, the angle of view is 100 * 84 degrees V*H (assume I am holding the camera in the portrait orientation). I would like to mimic the perspective of this UWA lens by shooting 3 frames with my 18mm lens (angle of view 67 * 52). If I shoot the 3 frames in the scenery orientation (not portrait) and assume 1/3 overlap for stitching, I should end up with an image with angle of view = 52*3*.67 = 104 deg vertically and 67 deg horizontally. So two questions: (1) Is the above math correct (ignoring small differences)? (2) Will the resulting stitched image have the same appearance (perspective) as the image taken with a 10mm UWA? I realize this procedure only works on stationary subjects and there will certainly be some loss of spontaneity / creativity. I am looking forward to posts regarding tall buildings and the PS rituals that will be required. BTW, I have shot a couple of test images and stitched them with MS ICE. They look good to me but, of course, I have no UWA with which to compare. I am pretty "thick skinned" so feel free to have at me :-)
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Bert