Hi Jason,
I just sent you a 2nd PM with some preliminary thoughts regarding the Leica Lux 21 & 24mm lenses vs. their slower counterparts, so I won't repeat most of what I wrote in the PM, here....(meaning I'll leave out commenting on the 21 & 24mm Luxes).
Since you're using a M8, I know you realize you have the 1.3x crop factor to deal with. You mentioned that you love your Zeiss Zf 21mm on a DSLR. To achieve a similar field of view on the M8, you would need to use a 15mm or 16mm lens, which after the crop factor is taken into consideration,, results in a 20/21mm field of view. Your choices for 15/16mm is somewhat limited. There is the CV 15mm f4.5, which although is relatively inexpensive, does have some red edge issues when used on the M8. The Zeiss 15mm f2.8, which is superb but extremely expensive and not rangefinder coupled, meaning you have to zone focus or estimate camera to subject distance (although of course depth of field is great). Lastly there is the Leica WATE (16/18/21mm f4 lens). It too is expensive, optically superb and a bit of rigging is required to efficiently mount the required UVIR filter. Lastly there is the Zeiss 18mm f4 (and Leica's 18mm f3.8)...both exceptional and will yield a field of view of a 24mm lens. I prefer the Zeiss as many do, not only for it's relatively low cost compared to the Leica, but much lower distortion.
I already discussed some thoughts on the wide angle Lux's you mentioned in the PM to you. On a M8, to get a field of view of a 28mm lens, you would use a 21mm lens. As others have mentioned, the Zeiss 21mm f2.8 is superb and from personal experience gives Leica's 21mm f2.8 Elmarit-M a run for its money...maybe even better in some respects (in the outer zones). Since the M8 has internal framelines as wide as for a 24mm lens....some do not use an external viewfinder when using a 21mm lens with the M8. They look at the whole frame and visualize a bit more. This works for some but not others...its a personal choice.
Now for 24/25mm lenses on the M8 (resulting in a approx 32mm field of view, the Zeiss 25mm f2.8 and Leica 24mm f2.8 are extremely close in performance, both wide open and stopped down. Just a different look but I feel each are some of the best lenses in their respective focal lengths. So is the new Leica 24mm f3.8.
In terms of 28mm lenses (resulting in a field of view of approx 37mm), there are many great ones. The older CV 35mm f1.9 is of low contrast wide open but a very good lens stopped down. The current CV 28mm f2 is also excellent but suffers from focus shifts. Both these CV lenses are softer in the corners that the Leica 28mm f2.8 asph (a very high contrast lens that's extremely sharp edge to edge) and then the legendary Leica 28mm f2 cron asph...almost without fault. The zeiss 28mm f2.8, I have little experience with, but from what I hear, it's good, sometimes soft in the corners and not everyone's favorite Zeiss among Zm lenses.
When it comes to 35mm lenses on the M8 (resulting in a field of view of approx 47mm), there are dozens of great choice to fit every budget. Personally (and many will disagree with me), I am not a fan of the CV 40mm f1.4 but it does have many positive attributes. I'm not fond of its bokeh nor its focus shift. It is though a very sharp lens.
I do favor the Leica 35mm f2 cron asph, its predecessor, the 35mm Cron Ver. IV, the incredible CV 35mm f1.2, a best buy in both it's speed and near perfect performance for the money....but its a very big lens close to SLR size. Then of course there is the Leica 35mm Lux asph Ver I and the new II. Both are tremendous but some Ver I's, depending how they are adjusted can exhibit varying degrees of focus shift.
In 50mm lenses, there are almost too many too mention. For a budget, the CV 50mm f1.5 is astonishingly good and close in sharpness to something between the current Leica 50mm f1.4 Lux asph and it's predecessor, the great 50mm f1.4 Lux pre-asph. The Zeiss Plannar 50mm f2 is one of the best 50mm f2 lenses and a best buy and the Leica 50mm f2 Cron is a classic and almost neck and neck. The Zeiss 50mm f1.5 Sonnar, is more of a unique specialty lens in the way it draws and does have focus shifts.
Lastly I'll mention 75mm, leaving out the Leica Lux f1.4 since its more of a portrait lens (a superb one at that). The Leica Cron 75mm f2 in terms of sharpness/speed, may get the nod for being the best...up there with the Leica 50mm f1.4 Lux asph. The Cv 75mm f2.5 is an all time best buy and is very close to the Cron in performance in many ways except it does often have a fair amount of CA when used wide open. The current summaraits like the 75mm f2.5 is also superb at a lower cost than the cron.
I didn't mention the other Leica Summarit lenses (the 35, 50 and 90), but they are all very good to excellent and much has been written about their cost/performance ratio.
I know I left out dozens and dozens of everyone's favorites. This was just meant as food for thought...or as for some of us, becomes our "only food", after we spend for some of these lenses.
Have fun!
Dave (D&A)
