I performed this test essentially to verify the possibility to calibrate the infinity point of the tri elmar 16-18-21 in order to avoid refocusing after focal change
due to usual tolerances in fixed adapters. I used the fixed Novoflex as a reference
and compared it to Voigtlander and Hawks helicoid adapters.
The helicoid adapters were tuned with the lens indicating the exact distance from
the target, to obtain best focus on the target positioned on center, while, from the same exact distance and the fixed Novoflex, focusing on center was performed with the lens.
Both helicoid adapters required a very small rotation, approx. a pair of millimeters, to reach the calibration point.
First crop is the center target, perfectly focused with the tri elmar at 16 F4 with
the 3 adapters, the other 3 are extreme lower left corner target crops with the 3 adapters.(the corner crops show the vignetting of the tri elmar at F4)
Unfortunately, the results for the helicoid adapters are unsatisfactory.
Center target- focus is identical with all adapters.
center by sergio lovisolo, on Flickr
Novoflex fixed adapter
novoflex by sergio lovisolo, on Flickr
voigtlander by sergio lovisolo, on Flickr
hawks by sergio lovisolo, on Flickr
The problem is progressively less evident with lenses of longer focal lens, and is nearly imperceptible from 50 millimeters.