There are two versions of this lens. The old C style lens was a 120mm f/5.6 lens and came with and without T* multi-coating. It was called an S-Planar. With the change to the CF style (and its successors) the optical formula was modified to a 120mm f/4 and all had the T* coatings.
These lenses are optimized for close focus performance and have a reputation for being soft at infinity focus. These characteristics may also be why it is popular with some as a portrait lens. I have not used either version, so my comments are based on the opinions of others. The f/4 version, being a stop faster, should be easier to focus.
I have the old C 120 mm 5,6 S-planarand at first I did have some problems as it is not very coated but the I got hold of a Pro Schade and it was a remarkable difference- much more deot/saturationand contrast- I love using it for pportraits - sometimes with a short extension tube 8/10 mm if I whant to get closer - The old C 250 mm 5,6 sonnar is great to - and it is sharpest wide open! - some parts for the older C lens lineup are harder to get as spares so you should probably considder a T* Cf lens as it will be easier serviced - the 120 is not like when you buy a 100 macro for a canon eos and bang you have 1:1 straight away- you will need som extension tubes or bellows to shoot macro. they are not cheap
> It seems the only real advantage of a 1:1 macro/makro lens is > convenience, as they simply allow the barrel to be racked out, giving > extension that can also be added with tube or bellows. Given how cheap > (relatively) 2nd hand extension tubes are, there might not be much > market for it for manual cameras! It is the old problem for > Hasselblad...decades of perfectly functional gear building up and > tempting buyers.
Presumably a 1:1 macro will have to be bigger, too, to allow the 120 mm of extension. Situation might be different for autofocus, as extension tubes would need to have all the linkages etc. and there might be better reason for having it all in the one lens.
Lastly, I am not holding my breath for innovative products for the V system!
Nowadays, high magnification is not achieved by adding extension, but by changing the focal length of the lens.
A 1:1 120 mm macro lens may be a 120 mm lens when set to infinity focus, but not at 1:1.
This (changing relative positions of lens elements) may be a good thing, or a bad thing.
A bad thing when they only care about "getting closer".
A good thing, because they can (at the same time as producing a lens that "focusses closer") keep a lens well corrected throughout its focussing range.
It is a very bad thing for people still using hand held, (i.e. non-TTL) meters, since the well-known formnulae used to calculate for exposure compensation do not work when you never know what the actual focal length of a system is, how the relative changes of elemens inside the optics affects f-number, and how much extension is used at any given time.
The best, no, the only way to use your 120 mm Makro-Planar is by adding extension.
But don't think that new lenses today need a lot of extension.
Techniques of building optical systems that are not a rigid arrangement of lens elements, but allow for nice things to happen by changing positions of these elements relative to each other too have taken off big.
For instance, how else can you have a fast autofocus lens if not by just moving part of a heavy lens?
The same "trick" was first employed in making zoom lenses, elaborated in constant-aperture zoom lenses. Next there were "floating element" lenses. Then floating elements and cell focussing (in which one element or one group of elements was moved relative to the rest of the lens elements) were combined.
Finally combine all three, and you get modern lenses. Very complicated, but thanks to brute force provided by computers, not a problem.
New macro lenses are not rigid things that are put, as a whole, at ever increasing distances from the film plane, but are devices in which by shifting lens elements relative to each other, focal length (and with it magnification) changes.
The new H-series 120 mm macro lens is such a new-fangled beast. It certainly does not come with 120 mm of extension built-in.
it being an auto-focus lens too, the mass of the part that has to move to focus has to be small. So it is a "front focussing lens", i.e. only the front group moves, relative to the rest of the lens. Not the entire lens relative to the film.
Your 120 mm Makro-Planar does the latter: it moves as a whole, away from the film, when focussing closer.
The 120 Makro-Planar is perhaps the better modern lens for 120 film format. It is only surpassed by the old 105mm Voigtlander Apo-Lanthar, perhaps the better lens ever created for b&w film. But it's near impossible to find one of these in perfect working condition, and the price is prohibitive.