Quote Originally Posted by 25asa
With the converter I shot frames at 5.6 (11), 8 (16), 11 (22), . .up to 45 (90)
Without the converter I shot frames at 11, 16, 22, 32, and 45 to coincide.

Magnifying the bricks to where they are the same size, the 2x converter shots show better resolution and accutance.
The most obvious thing is the area of film you're using.

If you're magnifying/cropping to the same final image, then the 2x image is using the full 66 frame, while the regular image is cropped so you're only using the centre - perhaps equivalent to a 35mm neg.