Note: I'll be away on a trip for a few days. Amateur Nikon should be back in action in about ten days.
Today's article is inspired by a comment I saw on a photography forum. There, someone advised another photographer to avoid third-party lenses because they supposedly are very bad when it comes to chromatic aberration. Of course - as I mentioned there as well - this is utter nonsense. You can't make such a comment any more than you can claim "Nikkor lenses are very good when it comes to vignetting". What you can say is something like "Lens A is better than lens B when it comes to element C".
|Taken with a Sigma Super Wide AF 24mm f/2.8. I find it better than the Nikkor of the same generation.|
To me (and to many other photographers out there) it seems self-evident that a third-party lens isn't always either worse or better; it depends on the design. But I realized this isn't necessarily known by a quite significant number of not-so-experienced photographers. The options are endless, but this also increases confusion. So, let's get to the bottom of this.
Optical DifferencesNon-existent. Period. Of course there are differences between various lenses, that's not the point. But it's absolutely untrue to claim something like "Sigma lenses are good/bad/ (or: better/worse than Nikon) when it comes to sharpness/vignetting/chromatic aberration".
These kinds of blanket statements are absolutely unfounded, and you should never believe them if, for instance, a salesperson tries to throw them at you. Sigma (and Nikon; and Tamron; and Tokina) make cheap and consumer lenses - where more corners have to be cut - and they make expensive and high-quality lenses - where you can pretty much expect the best.
Some individual lenses can be better at something, of course. But never spend more than a moment on claims such as "Buy Nikkor, they are always sharper than Tokina".
Mechanical DifferencesHere things get more complicated. The reason is that Nikon's mount has to be reverse-engineered by third-party manufacturers. As a result, it is not unheard of that there might be compatibility issues. For instance, some older Sigma HSM DG EX 50mm f/1.4 don't autofocus in live mode. In some other cases, with some really old AF Sigmas, they don't autofocus at all. Generally speaking, you can expect a modern lens to function with a concurrent camera (but if Nikon does something one or two generations down the line, they might suddenly stop functioning). Manufacturers (in our case Sigma, Tamron, or Tokina) usually can fix the issue easily (and often for free), so it's not a big deal. Still, it's something to keep in mind.
All in all, however, I do believe in third-party lenses. Many of them (especially in DX) offer solutions than Nikon has snubbed altogether. In other cases, they offer truly competitive alternatives. The Sigma 85mm f/1.4 comes to mind (not to mention the Samyang 85mm f/1.4, which costs 1/8 of the Nikon and is almost as great optically).