I have the S100 (as well as the H100 2.2 and the 90 SL APO) - it has the Leica S lens look - buttey bokeh, high microcontrast, very low CA, but not as clinical as the most modern portrait lenses for the X system I saw. I didn't look too much into the 80 1.9, but more the 90V and the samples I saw there look almost too clinically sharp to me where they have a digital look almost. More leaning towards the SL APO.
It is markedly better than prior existing 100mm ish wide open aperture alternatives for MF. Because of I think some ULD glass they added and of course because of Karbe's Summilux DNA infused in the S lenses - clearly a step up from the 110 2.0 from Zeiss. The bokeh is just butter with the background melting away into organic color patterns (see image below - like a Summilux 50 portait OOF).
Important to note is that charts only tell half the story with S glass, the OOF and sharpness falloff is beautiful with this one; gentle and perfect in its imperfectness vs. newer APO stuff. There's a reasons S lenses have been rehoused for large format cinematography arrays. I think you get a unique look with the S100 which is different from the Hassy stuff which reminds me more of the Leica SL lenses which are absolutely great technically, but quickly look like plastic generic portrait portfolio pics you can find on a flickr of a hobbyist photographer who photographs a local model.
I do not have permssion to share the full shot, but wide open this lens is incredible:
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In contrast, from the Hassy files I've seen, they are more clinical, meaning a bit sharper with less character, ie more "perfect" like Leica APO SL lenses which I do not like so much somehow.
I find the S look to be cinematic. With that lens, its not about AF for me, most of the time it is controlled portraiture and NOT action or moving fashion shoot.
It is markedly sharper than the 100 2.2 which I also own and also better controlled and sharper than the 110 2.0 from the V system.
Its a fabulous lens and a while back there was a thread from Matt where he compared the V and S lens.
Maybe this shows a bit the character:
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The bokeh is to die for. No CA almost and if so it is very subtle and a bit more of the pleasing green kind - its due to the glasses Leica uses. Wide open. The OOF and falloff makes it look more analogue and cinematic - ie not too abrupt and not too sharp of a falloff with subtle pleasing CA in highlight areas.
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In my book it is one of the best portrait lenses in MF land ever made and worth every penny if you own an S.
Stopped down the lens is perfect across the frame, of course with no CA especially in difficult sun lit reflective white surfaces, which is quite impressive. That's F5.6 shooting a building from the hip, top corner.
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This lens, alongside the S24 which is also perfect across the frame wide open, are the standout optics from the S system.
As soon as the S4 comes, these are the first lenses I'll slap onto the new camera body.
God-tier, frankly. Hat off to Peter Karbe on this one.