Test results from 80 / 150 Schneiders with 1.4x converter I tested on Acros 100 in a fine grain developer on a sturdy tripod and with mirror lock up etc. For the 80 and 150 I full-framed my USAF resolution test target and exposed at f4 and f11 and then without moving the tripod, slipped on the 1.4x and took the same photo, at f5.6(f4 on lens) and f16(f11 on lens).
In the darkroom I printed a maximum enlargement for the shots taken without the 1.4 converter and then reduced the height of the enlarger so that the images taken with the 1.4x were the same size on paper. The enlarger lens was a Nikon 80mm, set to its optimum aperture of f8.
The negatives were also examined under a x100 microscope too.
In both cases the prints from negatives taken with the 1.4x have better resolution and marginally less contrast, more so in the case of the 80 / 1.4 combination. Clearly grain was proportional to negative enlargement and more importantly, if these images were to be scanned, my effective scanner resolution would be reduced by 30% if I were cropping the shots taken without the converter, which is critical if you are using one of the cheaper flatbed/hybrid scanners.
Under the microscope, the film is almost at the limit of its resolution. If the converter was perfect, I would expect about a 40% increase in resolution, along with the image magnification. It looks like I'm getting closer to 25%, not bad. Edge resolution was similarly impressive. Having said that, Acros 100 has high resolution, so practically, with colour materials or faster film, it will always be the film that will limit the ultimate resolution, making the quality gap larger between the results ( I think)
Overall I'm very impressed with its effectiveness and it will be interesting to use it on a 180 or 300 if I ever get lucky on ebay!