Originally posted by wlachan I think the biggest con of Tamron/Sigma is their sub-standard built quality which may not be obvious on the outside but reflected by their prices. You really have to baby them or they can suffer from optical misalignment easily.
I don't think you can generalise that much.
There are very well-built Sigma lenses and some very cheaply-built Pentax lenses. You'll have to take two concrete lens models and then make a statement. A general statement just referring to brands is not possible, AFAIC.
Besides, I'd never be rough with any lens, even if I knew that the internal built is sturdy. Why would I risk some misalignment even if the risk is smaller than with a cheaply built lens?