flavio81
Member
I got this Sigma 28mm 1.8 (aspherical) for cheap and i wonder how much edge in terms of AF speed, reliability and image quality am i losing out on compared to the Nikon AF-S 28mm 1.8 G, while shooting with a F100? Can this even be determined?
It depends.
For example the newest "G" Nikon AF lenses have mostly very good optical designs, at the expense of being UGLY AS HELL, and unusable on most analog cameras because of not having an aperture ring.
But even Nikon, even in the "G-series" era, has made some "dogs", that is, lenses that are underperforming. This is an excellent chance of going for an alternative brand like Sigma. A classic example of a "dog" is the 1960s' Nikkor 43-86/3.5 zoom. Another example is the early Nikkor 35/2.8 lens (Note: This pre-AI lens went through several optical designs in its lifetime, so perhaps there are also very good 35/2.8 variations.)
In the G-series era an example of an underperforming lens is the 24-120 "VR" "G" lens.
So in those cases there is a big chance than a competing Sigma or Tokina or Tamron lens could be better. Tokina is a very respected manufacturer and their pro lenses have very good build quality. Current Sigma 'ART' series lenses are also offering something that not always is offered by a manufacturer: Lenses that are designed for all out performance disregarding compactness or weight.
Now, going back to the 60s-early 70s the picture is very different and i don't think you could say that any third-party lens of the "Sun" or "Spiratone" or "Carenar" or "Samyang" (and many other) brands could be better or even as good as a Nikon/Canon/etc lens. In particular if the lens was made in Korea, then even worse performance.
Mid-70s Vivitar made a hit with the Series 1 lenses, but those lenses weren't really inexpensive. Later in the 80s Vivitar retained the "Series 1" labeling for sub-par lenses, so watch out.
There are some third-party lenses that have well established reputations, such as the 90mm macros by Sigma/Tamron/Tokina/etc.
Personally, i only owned one third-party lens, a Sigma "Super-Wide II" 24/2.8 for Nikon AF-mount. It was compact, reasonably well built, contrasty, and very sharp in general. The downside is that it had quite pronounced distortion. My favorite 24 was the Canon FD 24/2.8 and that one was compact, well built, contrasty, very sharp AND with zero distortion, so in the end i sold the Sigma.
But the Sigma was a good lens and indeed i've seen some good pictures made with it.