Originally posted by Edgar_in_Indy The small size of the Ltd's is a truly unique and compelling feature for a lot of people. But lenses always make tradeoffs, so you pay for the small size in areas like vignetting, and perhaps border/corner performance at larger apertures.
I agree, any lens design is a tradeoff. Pick the one you prefer.
Originally posted by Edgar_in_Indy Sigma makes their fast primes huge for a reason,
Yes and that reason is mostly FF coverage, except in a few cases. That's also a why you would chose (or reject!) Pentax lenses: they are targeted to APS-C. That's why the DA 55-300mm is more compact than the Sigma/Tamron 70-300mm. Now Sigma and Tamron are putting stabilization in their lenses, unfortunately for Pentax because they don't really need it (except I'd say for tele) and it makes the lenses bigger (and more expensive!).
Originally posted by Edgar_in_Indy and like the person a few replies up, I would generally favor no-compromises IQ over a compact lens.
There's a place for everything and I don't see too much compromises in the Ltd lenses.
In my lens line-up I always compared to 3rd party before buying. I didn't put too much emphasis on price (except if the difference is really big) but on features and IQ. Examples:
I choose the D-Fa 100 over the Tamron: longer, quick-shift, smaller, IQ a wash.
DA* 16-50mm over Tamron 17-50: WR, SDM, wider, IQ pros and cons.
DA*50-135mm over nothing, in 2008 no 70-200mm f/2.8 were available, the DA* 60-250mm was again delayed. Do not regret it: superb IQ, much smaller than 70-200mm or 60-250mm.
DA 12-24mm over Sig 10-20mm, quick-shift, constant aperture, better IQ (slightly)
DA 55-300mm, compact, more useful range over the 70-300mm
Sigma 30mm f/1.4 over FA 35mm f/2, faster, wider.
Sigma 8-16mm over 12-24mm, much wider, HSM, much much wider.
The Ltd primes: no competition.
My father-in-law for who the value is more important:
Tamron 17-50mm, Tamron 90mm macro, Sigma 10-20mm, Sigma 28-105mm, Pentax 55-300mm, Pentax FA 50mm f/1.4.