Sometimes haze can be removed easily by a technician; sometimes not.
According to Skyllaney, what's happening to the early CV lenses (in LTM and S mount) isn't haze, it's an issue with the glue/cement between some of the elements. This makes it unrepairable without separating the elements, cleaning, repositioning, and recementing them - not impossible, but close enough that it might as well be.
I have the original 15/4.5, 21/4, and 28/3.5 lenses in LTM. My 21mm is definitely slightly "hazy", the 15mm seems fine, and the 28mm is clear as a bell. I'm not sure what causes the cement to go cloudy, but it does seem like a bit of a roll of the dice. I've seen a lot more of the LTM 35mm Color Skopars with "haze" than anything else, for what it's worth.
As for performance: these early lenses all have issues on digital Ms when used for colour photography (the "Italian flag" effect), where the new ones don't. Rendering and sharpness is solid across the board, even with the mildly hazy 21mm.
I'm always impressed with how rectilinear the 15mm Super Wide Heliar is (just pay attention to the angle of the camera to avoid converging verticals), and it's surprisingly good at the corners:
(Leica M240)
The 21mm has some barrel distortion, but in most scenarios, it's not noticeable. This is very much worst-case scenario - and you can see the "glow" from the "haze" here:
(Leica Ic, Fomapan 100 in Rodinal)
The 28mm Color Skopar is my favourite of the lot. It's a lot more manageable than the 28/1.9 Ultron (which I thought was huge on a screwmount Leica, and has a lot of finder blockage on an M, from what I remember) with a short 90º focus throw and a little focusing "nub", making it very fast to use. Contrast is predictably a tad higher than my other LTM lenses, but nothing overwhelming. It's a pretty solid all-purpose lens; I generally prefer 50mm as a focal length, but I've never used the 28mm Color Skopar and thought "well, that looks terrible". For comparison, it's a lot better edge-to-edge than the Pentax SMC 28mm in K-mount I used to use on the KX and MX years ago, and when I did some informal side-by-side comparisons with the 28mm Color Skopar at f/4 on film with Fuji's X-mount 18/2 on an X-Pro 2 at the same aperture back in 2020, I found the Skopar was better in the corners there, too. It's a fantastic lens, and I'd be curious to see how the new f/2.8 version compares with the original side-by-side.
(Leica Ic, Rollei Retro 400S in LC29)
(Leica Ic, original - i.e. non-Kentmere - APX 100 in Rodinal)
Just bear in mind that both the 21mm and 28mm Color Skopars (and I believe the 25mm Snapshot Skopar, if I remember right) have a weird "hood" that's just a thin metal ring. This is the worst part of these lenses - it's small, compact, and looks tidy, but they're such thin rings that trying to remove them by gripping them like a normal hood to unscrew them will typically cause them to deform and bind on the threads, making them feel stuck. The secret is to grip them all the way around and avoid squeezing them at all; you need a super-light touch, and when you're trying to remove them in a hurry to swap a filter out, it's easy to forget this. They're all so flare-resistant that you probably don't need the hoods, but not using them leaves a weird exposed thread and prevents the cap from fitting correctly - not ideal.
Jenny by Jim Fischer, on Flickr
House Plant by Jim Fischer, on Flickr
Jenny by Jim Fischer, on Flickr
