The first series covers 2-cam, 3-cam and 'R-only' mounts. The later ROM-compatible lenses are part of the 2nd series of 28mm Elmarit lenses.
Leica Order No. - 11 204 - 11 247 - 11 529 - 11 206-Safari /LLC - 148
Production era - 1970-1993 < 51,010 lenses
Variants - 2-cam, 3-cam and R-only; black and olive green "SAFARI" version
Number of lenses /groups - 8 / 8
F stop range - f/2.8-f/22
Closest focusing distance - 30 cm / 11.81 in
Smallest object field - 168 x 282
Diaphragm setting /type - 8-blade
Angle of view diagonal - 76 degrees
Filter type - Series 7 filter held in place with hood
Accessories - Hood: 12509, Front cap: 14172
Materials -
Dimensions length x diameter - 40 x 63 mm / 1.57 x 2.48 in
Weight - 275 g /9.7 oz
Inscription - ELMARIT-R 1:2.8/28 LEITZ WETZLAR 2XXXXXX
Designer - Rudolf Ruehl - 1970
This lens is of Wetzlar origin, and should be one of the lightest lenses for the R-system with less than 300grams. It is also very compact and has vignetting of 2 stops. It is of comparable performance of the contemporary M-28 (2), with a slight advantage for the R version in the field, where details are rendered with higher contrast. At full aperture we have low to medium overall contrast and the rendition of fine detail on axis (to image height 6mm) is quite clear, becoming very soft when approaching the corners. Stopping down enhances micro-contrast, but the definition of image details improves marginally.
There is a fair amount of field curvature and this limits the improvements when stopping down. At 5.6 the depth of field covers some of the detail softness in the zonal areas and fine detail is now rendered with clean edges.
Close up performance is fair at best and stopping down a few stops is necessary for good imagery. Wide open the lens is flare sensitive and small bright spots have extended blur patches. During its course of life, there have been some changes in balance between centre and edge performance. For really critical work, this lens should be used stopped down to middle apertures.
As noted above, there are multiple versions of this lens in its native R-mount format, with varying numbers of cams available on the back, which mostly do not affect its operation when converted to Pentax K-mount.
The ROM version of this lens (not currently pictured above), is a complete redesign of the lens with an integrated hood and reputedly sharper image output. More details of the ROM lens available at
http://www.l-camera-forum.com/leica-wiki.en/index.php/28mm_f/2.8_Elmarit-R_II
Technical data referenced from l-camera-wiki at
http://www.l-camera-forum.com/leica-wiki.en/index.php/28mm_f/2.8_Elmarit-R_I
Text referenced from Erwin Puts' Leica Lens Compendium, available electronically at
http://www.furnfeather.net/books/pdf/llcforweb.pdf 
