Since I like to take closeup photos of flowers and other motives, I tried to answer the question, which of my Mmount lenses can be used for this purpose (the shortest distance values of the lenses suggest that I cannot use any of them...). Therefore, I made comparison photos at the shortest possible distance and also calculated the maximum magnification of my lenses.
Note: The formulae used for the calculations in the table below can be found on page Calculating Minimum Object Size and Magnification.
Lens  Mount  Focal Length 
Angle of View 
Min Distance 
Smallest Object Size 

FullFr. Format  APSC (DX)  FullFrame Format  APSC (DX)  Technical Data (FF Format) 
FullFrame Format*  APSC (DX)  
Voigtländer Super Wide Heliar  M bayonet*  15 mm  22.5 mm  110° diagonal  87° diagonal  0.5 m  1106 x 737 mm 1:31** 
732 x 488 mm 1:31*** 

Zeiss Biogon T* C  M bayonet  21 mm  31.5 mm  90° diagonal  68° diagonal  0.5 m  775 x 516 mm 1:21.5** 
523 x 349 mm 1:21.5*** 

Voigtländer SnapshotSkopar  M39  25 mm  37.5 mm  82° diagonal  59° diagonal  0.7 m  934 x 628 mm 1:26** 
615 x 410 mm 1:26*** 

Minolta MRokkor  M bayonet  28 mm  42 mm  75° diagonal  54° diagonal  0.8 m  951 x 634 mm 1:26.4** 
627 x 418 mm 1:26.4*** 

Zeiss Biogon T* C  M bayonet  35 mm  52.5 mm  62° diagonal  44° diagonal  0.7 m  652 x 434 mm 1:18** 
439 x 293 mm 1:18*** 

Zeiss Sonnar T* C  M bayonet  50 mm  75 mm  46° diagonal  32° diagonal  0.9  592 x 395 mm 1:16.5** 
395 x 263 mm 1:16.5*** 

Voigtländer Color Heliar  M39  75 mm  112.5 mm  32° diagonal  21° diagonal  1.0 m  444 x 296 mm 1:12** 
293 x 195 mm 1:12*** 

Leitz ElmarC  M bayonet  90 mm  135 mm  27° diagonal  18° diagonal  1.0 m  372 x 248 mm 1:10** 
244 x 163 mm 1:10*** 

Leitz TeleElmar  M bayonet  135 mm  202.5 mm  18° diagonal  12° diagonal  1.5 m  330 x 220 mm 1:9.2 
368 x 245 mm 1:10** 
244 x 163 mm 1:10*** 
*) Or: Mmount
*) Calculated for a sensor width of 36 mm (note that
the Leica M (Typ 240) has a sensor width of 35.8 mm)
**)
Calculated for 35 mm according to a simple formula on
the basis of angle of view (technical data) and shortest distance (technical
data); please note that these values are just estimates
***)
Ditto, recalculated from sensor format and shortest distance (technical
data); please note that these values are just estimates
My calculations reveal that the magnification of a lens is independent of the sensor (film) format (given the same aspect ratio), but, of course, the angle of view and the smallest object size are different (because of the crop).
When starting from film/sensorrelated data, both Leitz lenses deliver identical values for the smallest object size and magnification. They are also the lenses which deliver the highest magnification for closeup photography.
Note: The formulae used for the calculations in this table (rightmost column) can be found on page Calculating Minimum Object Size and Magnification.
Here are comparison photos taken with my Mmount lenses where I tried to photograph a scene at the shortest possible distance (and in most cases at the maximum aperture):
Note that the Voigtländer SnapshotSkopar25mm f/4 is missing here, because I bought it after this test was performed. It comes close to the Minolta MRokkor (1:26 versus 1:26.6 for Minolta).
As a rule of thumb, the test photos reveal that the shorter the focal length of the lens from my collection, the less the lens is suited to closeup shots. This is reflected in the magnification values that I (mostly) calculated. Somewhat disappointing in this respect is the Minolta MRokkor 28mm f/2.8 (the missing Voigtländer SnapshotSkopar has a similar closeup performance but has a shorter focal length), which is topped by the Zeiss Biogon 21mm f/4.5. The Voigtländer Color Heliar 75mm f/2.5 is better at closeup shots than all the wider lenses  it comes in third  but it cannot compete with the two Leitz tele lenses, although it is not too far away from them (1:12).
The two Leitz lenses are suited to closeup shots best, although a magnification of about 1:10 is also not impressing. Their technical values are more or less identical, but due to their different focal lengths (90 mm and 135 mm), both differ with respect to perspective and thus background blurring. While the ElmarC is more handy (lighter, smaller), the TeleElmar provides a better separation of the foreground object from the background.
All in all, either of the two Leitz tele lenses is suited to "moderate" closeup photography. Setting the focus correctly (and manually), is another story, though... But both lenses have a focus ring with a small thread pitch, which makes focusing easier: The distance scale stretches over about 180 degrees, whereas it is about 90 degrees for all the other lenses (with slight variations), including the Voigtländer Color Heliar 75mm f/2.5.