ElectronGuru wrote in post #16185700It seems like this explains a bunch of questions...
For the most part, yes.
Why do most lenses wider than 50 have that big curve on the front ?
Likely, though a lens needs to be increasingly spherical to capture a wide field of view in any case.
Why are there no 24/35 1.2's?
Yes. Leica has a 21mm f/1.4, it's ridiculously big and heavy (for a Leica lens), and costs $6500, but it is possible.
Why isn't the 24-70II as awesome as the 70-200II?
I suppose it could be that telephoto lenses as a whole are easier to design than wides. Any camera system has decent 85/100/135/200mm lenses.
Why is there no 20mm pancake?
Likely, the 40mm is probably as wide as Canon could get away with in a pancake.
Why are wides larger/pricey, when they 'should be' smaller/cheaper?
Smaller, definitely, there are some tremendously small and quality wides out there.
Why isn't it easy to find an optically perfect wide?
For sure, a lot of people are having trouble finding good wide angles for the D800, which has 36mp resolution; tech cams can have up to 80mp of resolution and the wide angle lenses are still razor sharp to the pixel.
Why can they make such a small/sharp M wide and not do the same on EF?
Why do M lenses have a less 'lumpy' outer shape?
Can't comment on the M system.
BTW, if you wanted to put your knowledge (summaries of what you've put together) into a few guides, I'm sure we'd eat them up!
That would take quite a while, but there are already great sources that have compiled information with pictures and everything, a good place to start is Cambridge In Colour.
I should add that retrofocus is not all that bad with digital, because unlike film, which could accept light coming in from any angle, sensors like it when light comes straight-on. In a non-corrected wide angle, the light exits the rear of the lens at roughly the same angle it enters, and this could cause color casts on digital sensors, particularly those with micro lenses and/or non-100% fill factor. CCD sensor typically don't have micro lenses and have 100% fill, which is why most medium format back use them, and Leica used CCDs for while, until they developed their own CMOS sensor suitable for the Leica M lenses.
The retrofocus design makes the light rays hit the sensor head-on, which can solve a lot of problems with certain camera/sensor/lens combinations. To put things in perspective, a non-corrected Schneider tech cam wide lens can cost around $1.5~3k, in comparison a Rodenstock retrofocus tech cam lens of the same focal length is anywhere from $4~9k.