1. I really love the reviews on the DA* 50-135. Definitely a buy without question except the motor (SDM) breaks down easily. Wonder if it is true?
>> AFAIK, lots of folks here have been using theirs for quite a few years w/o issue. My bro has one and used it for a long time too.
The lemons seemed to be early batches and more common in the US (where you see most of the complaints)
Sometimes I wonder if the same lemons get passed around there due to their lax product return laws.
I'm sure you've heard of the stories of this sort
Eg.
Uni student "buy" high end Tux, use it for DnD, then return it as using "no questions asked" return conditions.
Fella 'buys' video cam to record his sons 1st b'day, then returns it as 'unsuitable' once the event is over and its purpose is served.
etc
So imagine you end up getting that '2nd hand' video cam sold as 'new'
Anyway, buy ext warranty if you want to dbl confirm
2. FA 31mm much sharper than 43mm, hence the price premium.
>> I've not compared. Won't bother to. Both are pretty sharp from wide open.
Sharpness is not the only thing on a lens.
The FA ltds are a balance of size (just look at the humongous Canikon lenses), build quality, bokeh, fast aperture, contrast and sharpness.
IMO, FA31ltd is a rather fast wide angle lens on FF. Hence the price delta.
3. I would like a fast lens but seems that the F1.4 lens are soft wide open and sharpest at F2 and above.
>> All lenses (with some exceptions) are softer wide open regardless of brand. Most cases at wide open, the lenses have a lack of contrast and can benefit from the use of a hood.
IMHO, you need to be realistic on the expectation on sharpness. At the end of the day, its the picture as a whole that counts and a lens at f1.4 may just help you achieve that look you are trying to achieve. No point just looking for sharpness if the picture/effect is not as pleasing.