Hi Jes. Merry Christmas !!
First I would like to be fair to Sigma lenses , they are not the best that you can put in front of your camera but they are way , way, ahead of those Jupiter and old Zeiss from Democratic Germany . Some Sigma lenses are indeed very good . The 50 Macro is very good and so is the longer one , the 105 , I believe, and probably better than any old Japanese lenses of older generations.
Having said that , Leica lenses are in a different category that no other lens manufacturer even approaches , because Leica design philosophy of Sharpness and Resolution first, is in line with the old German tradition of fine engraving and printing ,and this is very different than the Japanese tradition of Drama and high Color Contrasts , that permeates Japan's lenses and Saturated Film emulsions , as it does their Stage Histrionics.
Zeiss design philosophy got stack in the 1950 in an obsession for Chromatic Aberration corrections , via the endless addition of glass elements ,to correct other glass elements . This is in line with the German Stubbornness that typically starts with the wrong approach , ( Like rear Air Cooled engines in VW cars ) and optimizing to perfection, before pursuing the right approach ( Front water cooled engines VW). ,This produced well corrected lenses that , consequently , exhibit an untamable Blue coloration , since blue being the highest energy component of light , is the only color that survives after going trough Dozens of energy robbing glass elements.
Leica sees light as a Flow of Energy through the lens and makes all efforts possible not to disturb that flow . No changes in direction , minimal amount of lens elements , perfect centering , making the Glass for the Design needs ,rather than accommodating the design to available glasses. Leica aims for even Spectral Transmission and Full corrections at FULL APERTURE.
The SD9 sensor is very much in line with Leica Philosophy , since it also thrives on Sharpness and even Colors , so putting the two together is like I said before , a match made in Camera Heaven.
The SD9 is the easiest mount to install and I am restarting production of this mounts soon after the Holidays.
Sigma SD9 with Leica 100 Apo Macro Elmarit and 2X Apo Converter
MERRY CHRISTMAS'S EVERYBODY !!