Leica makes only one prime R lens with 24mm focal length and this is it - the 24mm f/2.8 Elmarit-R. There is no 21mm any more in Leica's current R lens line-up and the next widest lens is 19mm - a big difference. So, the 24mm focal length can be a very useful one, especially if you already own a 35mm lens and feel that 28mm is too close, as I did. Optical performance of the 24mm Elmarit-R is quite respectable and certainly above average as 24mm lenses go. It's really a Minolta lens, made to Leica design and QA standards. It's an old design and it shows! Performance isn't bad by industry standards - it just isn't brilliant. I found that the 24 Elmarit-R doesn't quite give the resolution, contrast and brilliance of color that one normally associates with Leica optics. Colors are faithfully rendered, however, with the usual Leica neutral character. It would be typical of a lens of this type to give some barrel distortion; I daresay it does but, if so, it's slight and I've never noticed it. There again, I've never used it with a subject where barrel distortion would be obvious, such as a brick wall or with a vertical pillar at the edge of the frame. At full aperture, the rendition of detail is noticeably softer at the edges than at the center, there is quite a bit of vignetting and contrast falls off noticeably at the edges. Performance can be improved significantly, however, by stopping down to f/5.6 or f/8. This is unusual for Leica lenses; most are almost at optimum performance wide open and this is an important property that distinguishes them from other manufacturers' lenses. The optical formulation consists of 9 elements in 7 groups. This includes floating elements, which help to maintain the optical performance at close range. Closest focus is 30cm and smallest f-stop is f/22. The 24 Elmarit-R is relatively compact, with length of 48.5mm, width 67mm and weight 400
gm. To avoid flare with side lighting, it really needs to be used with the separately sold rectangular shade. I've always used the shade and never encountered flare. However, I never took a shot that was likely to induce flare, such as with a bright light source in the field of view. The shade includes a knob that can be turned to rotate a polarizer if fitted. Filter size is 'series 8', which means that the filter doesn't have a screw thread but is sandwiched between the shade and the end of the lens barrel. The 24 Elmarit-R is quite expensive and retails for around 1,250 GBP. However, excellent examples can be purchased for under 700 GBP on the used market. For more flexibility (and probably better performance), Leica now has a 21mm-35mm f/3.5 Vario-Elmar-R zoom lens. Retail price of this zoom lens is about the same as the 24mm Elmarit-R. I haven't tried it but it seems like a bargain (for Leica!) and may just be a better buy than the 24mm Elmarit-R for many R users.