Originally posted by JHD If you buy an SDM lens, don't buy it used. Buy it brand new and get the longest extended warranty available, preferably one that can be renewed... to avaid being screwed!
That is one way to look at it, as there is certainly the possiblity that at some point the SDM motor may fail. However, in the long run there is still a strong argument to be made for buying a used lens if you're looking to save money, even if it is an SDM lens.
Let's say the DA*60-250 is $1200 brand new and $1000 used. Let's also say that a replacement SDM motor costs $200 to install. So if you buy the used lens and get unlucky and have an SDM failure at some point then you'll end up spending $200 to fix it and you'll have spent $1200 total, the same as the new lens. Now the percent of SDM motor failures isn't an unknown number, but in a worst case scenerio let's just say that 50% of SDM lenses have a motor failure (I would be shocked if it's really that high, it's probably closer to 10%, but let's just assume it's 50% for now). So half the time you buy your used lens for $1000 and are done. The other half of the time you end up spending $1200 (at some point) for the lens and a replacement motor down the road, but you're no worse off than had you spend $1200 on a new one.
In addition, extended warranties aside, if you spend $1200 on a new copy and the the SDM motor fails after a year (at least in the US), you're still going to end up spending the same $200 on a new motor and now you're in for $1400 total. If there are inexpensive extended warranties that can be purchased for these lenses then the argument to buy a new copy with the warranty might be the best move, however, if the cost of the warranty if more than $100 then the same numbers used in the above example would mean that in the long run the extended warranty is most costly (on average) than taking your chances with a potential failure (which is basically why places offer extended warranties, because over the long run they take in more money than they pay out).
But, at the end of the day, everyone has to do what makes them the most comfortable. For me, that usually means buying used lenses and knowing that given the spread in price between the two options, I should happen to run into a failure, I won't be in a worse position than had I bought new.