Hello,
I still do have Bessa II with Color-Heliar 105/3.5
Color-Heliar lens is actually a quasi "Soft Focus" lens, esp. between f/3.5 - f/8.

You need to at least use f/8 or smaller aperture to get acceptable definition for normal photography, however there still is some softness.
The softness esp. around f/3.5 - f/8 is coming from enormous amount of aberration of the optics.
Shooting night scenes at full open aperture can prove this.
This aberration also seems to contribute to weird "3D effect", which may be good sometimes (e.g. portrait).
This means the Color-Heliar 105/3.5 may have somewhat resolution but very little contrast.
Probably this type of lens is more suitable for LF rather than MF, which generally have use smaller aperture and can have more control.
Also, this Color-Heliar 105/3.5 has unacceptable amount of distortion which will be a really bad choice for architectural photographs and alike.
I will strongly suggest that you should not entirely depend on what generally thought correct on the Internet for the lens optical performance UNLESS YOU HAVE TESTED THE LENS by
checking the image structure on the film!!!
See the following links:
http://www.cameraeccentric.com/html/info/voigtlander_2.html
Even the Voigtlander says Heliar does not have a searing sharpness which means
?
They also quote Universal Heliar for real soft focus lens.
Voigtlander did also quoted in the old pre war II catalog that the Heliar are the Master Lens which will generate harmonious PLASTIC effect image, which they claim "artistic, which means that technically and optically it is indeed a low contrast lens (caused by residual aberration).
I only have Color-Heliar (integrated in Bessa II) but it seems that Voigtlanders (not Cosina Voigtlander) Heliar have a tendency to render some sort of plastic image.
See the following:
http://www.hayatacamera.co.jp/article/photo200504.html
http://www.hayatacamera.co.jp/article/photo200708.html
I dont know that this residual aberration was deliberately introduced in the design of the lens for Color Heliar / Heliar or not.
Also please remember in the old days, there was no Photoshop (R) or alike to manipulate images (expect retouching), so achieving some kind of effect by the lens itself may be more important than today.
I somewhat agree that Heliar type lens generally (but not all) gives a nice bokeh, but you have to think what you have paid for.
Also there is some lens that I find very good bokeh in Gauss (Planar(R)) type lens and even in other type lenses.
So why you have to limit yourself on choosing Heliar type lens?
Also remember that only testing the lens with various conditions will tell you the real truth.
Say, if someone is saying that lens AAA is good, but if he/she uses much smaller aperture than what you use most often, what that mean for YOU?
Even you say bokeh, there is a foreground bokeh and background bokeh, and it will be difficult to design a lens that have good for both foreground and background bokeh and also maintaining sharp image at the focal plane simultaneously.
Is the lens performance info on the Internet tells you
ALL about that for the particular lens that you are interested?
What bokeh at what aperture?
How is the bokeh of very high light intensity objects?
For these reasons, you may get some idea from the Internet for lens performance, but you may have to figure out by yourself, and you may have to test the lens by yourself in various conditions.
Also, the bokeh is very subjective, thus it is difficult to say lens AAA has a better / smooth bokeh than lens BBB so I cant say which lens has a good for bokeh for you.
NOTE: I dont mean that all "Heliar Type" lens is all soft, indeed I have once had Cosina made 50/3.5 Heliar (for Nikon S mount) and that was very sharp.
In realty, lens performance depends much more on the respective lens design not so much dependent on the type of lens (well, today lens designers wont choose a bad lens type anyway, right?).
It is 2011, not 1910s when Tessar (R) stand out from ordinary and meant to be a sharp lens.
For example:
Voigtlander also made an Apo-Lanthar which is nothing but the Heliar Type lens.
The one that I have is an Apo-Lanthar 105/4.5 integrated in the Bessa II, which is an incredible performer (and actually this is a rare Bessa II model, but it is the film camera that I most frequently use).
No halo, high resolution, outstanding contrast and low distortion which true APO regime lens only provides, but made with the optical glass including super-heavy-metal oxide (probably used in the one of the lens of the front group) which was cleverly used conjunction with the Heliar type design to achieve apochromatic performance.
Attached is the photograph taken with Bessa II Apo-Lanthar 105/4.5 @ f/4.5, 1/2 sec. Provia 400X (only correct verification of the lens performance can be assessed by x50 microscope using a better film e.g Velva 50 for sharpness, Provia 400X is too grainy and the scanner Epson V750 seriously impedes quality).
Sorry, you cant get this contrast from Bessa II with the Color-Heliar, absolutely no way and you will see the black sky much lighter with Color-Heliar @ f/4.5, which is a optical fault,
but will compress contrast range, which will somewhat explain the plastic effect.
I think that sometimes Color-Heliar 105/3.5 gives better background bokeh than Apo-Lanthar 105/4.5, but the optical performance at the focal plane when wide open is totally unacceptable, thus I seldom use Color-Heliar Bessa II (I frequently use aperture close to fully open so Color-Heliar is useless).
Also that great background bokeh of Color-Heliar is coming from what?
From the inherent soft focus / diffused nature around the entire image field which caused by flare from optical aberrations?
Apo-Lanthar 105/4.5 do have a very high contrast and very high flatness of field, which results a complete differentiation of focused and out of focused subjects that will create a dramatic effect in certain photographs, while Color-Heliar do not have that differentiation power but have a 3D effect and plastic effect originating from residual aberrations but almost useless between f/3.5 f/8.
Which do you like?
Apo-Lanthar 105/4.5 is definitely my choice, but be careful, if you use it for portraits, the unforgiving nature may show up in certain situations and I actually received a claim with this.
(Note that the attached photo doesnt seem to show much bokeh at the foreground, but note that this image was cropped heavily (about 2x, thus objects are quite far, since I am unable to use a tripod, I have to lean the camera to the tree) and the scan and jpeg compression decreased the resolution, but looking through the 10x lope, it has a uniform bokeh on the foreground object.)
Now you can understand that merely specifying "Heliar Type" lens isnt a guarantee for the performance you like.
Well, any particular lens type isnt a guarantee for performance you like, anyway.
It maybe better for you to forget about the lens type, and find the lens that you can accept per your performance criteria, which certainly need an effort to find it out.
If you really insist on Heliar type lens and if you are 35mm shooter, Cosinas 50/3.5 Heliar maybe good for you, and may be available on LTM.
Although 50mm lens @f/3.5 max aperture wont give much big bokeh at all.
Also there seems to be a Cosinas 75mm f/1.8 Heliar available in M mount but I cant comment any lens that I havent used.
See the following link for the gallery:
http://www.cosina.co.jp/gallery/kano-75/index.html
Regards,