I receive more questions every week about lenses than just about any other topic. I sympathize with all the questions because I struggle with making the same choices that you do. Should I buy the Nikon 24-70mm f2.8 or should I get the Sigma 24-70 mm f2.8 or the Nikon 24-85mm f2.8 – 4 or the Tamron 28-75mm f2.8? The cost of the Nikon lenses are always significantly higher than the TamronSigmaTokina lenses.
So what are you paying for when you buy the Nikon lens? In one word … Quality. In fact, Quality with a capital Q.
I currently own lenses from Nikon, Tokina and Tamron. In the past, I’ve owned lenses from Sigma, Vivitar and some other random brands that I’ve forgotten. Most of these lenses are the “professional” lenses from the manufacturers and are large aperture zooms or primes. In just about every case, I’ve found that the Nikon lenses have performed flawlessly. In all the years I’ve owned Nikon lenses, I haven’t had one single lens break down for any reason. I could attribute that to simple luck or to Nikon’s consistent quality.
On the other hand, at least 50% of the lenses I’ve purchased from the third party lens manufacturers have failed in some way or another. My Tamron lens hood cracked under light duty wear and tear. Another Tamron’s internal focus gears “skip” every once in a while. My Vivitar fell apart in my hands.
My Tokina lenses have all performed very well and have been a bright spot in my lens choices from third party manufacturers.
From a sharpness standpoint, all of the lenses I have purchased have been pretty sharp. In fact, many of the photos I sell or use in my books were taken with Tokina, Tamron and Sigma lenses. I haven’t run into any major issues with poor optical quality from these manufacturers. Therefore, I sometimes put up with a little bit of structural integrity problems because I paid a lower price for the third party lens.
When it all comes down to it in the end though, buying a Nikon professional lens will almost always be the better choice than buying a third party lens. As the old saying goes, you get what you pay for. This holds true in spades for lenses!
Here’s a link to a company who rents lenses to the public (thanks for the link Chuck!). They have an interesting commentary on Sigma lenses that I think you’ll enjoy reading.