Zack Zoll wrote:
I do believe that somewhere along the line, Tamron built or was contracted to build something for that lens.  Or perhaps they built nothing, but were brought in as consultants for the design.  None of these mean that the lenses are identical, but they all imply that some of the same minds are working on both of them, meaning that they would have chosen to solve problems in a similar manner - unlike a Tokina for instance, that shares no components or designers that I am aware of.

Um, Tokina was started by some lens designers who left Nikon. The Tokina 50-135 and Pentax 50-135 - there are a pair of lenses that show a single source.

photoimager wrote:

Um, Tokina was started by some lens designers who left Nikon. The Tokina 50-135 and Pentax 50-135 - there are a pair of lenses that show a single source.

That is true also they just don't make lenses for Pentax they business partners.

photoimager wrote:
That rubber gasket is for weather / rain sealing to prevent water ingress via capillary action, not of any benefit in the dry of a barn.

Maybe it wasn't built specifically to prevent dust from getting in the lens, but it sure had that effect.  The barn held several horses, and there was a ton of dust in there between horse dander, hay, and general barn dust.  All my D lenses had to be cleaned after 1-3 sessions in the barn, while the G lenses made it much longer between cleanings.  I can't tell you how long exactly, because most of them only got one cleaning before I moved on and wasn't photographing for them anymore.

The 85 f/1.4D had a larger-than-average gap in between the aperture ring and the lens chassis though - it's very possible that the G version stayed cleaner not because of the gasketing, but because the gap wasn't there anymore.

photoimager wrote:
Um, Tokina was started by some lens designers who left Nikon. The Tokina 50-135 and Pentax 50-135 - there are a pair of lenses that show a single source.

This is true.  But they were designers that left Nikon; it was some time ago, and lens technology has changed greatly since then.  Tokina still works closely with Pentax, and I don't know if they ever worked with Minolta, but I do believe that they worked with Sony as well - at least for the first couple years.

While Tokina may have ex-Nikon lens designers, there are exactly that - ex- designers.

I'm not aware of any Nikon lenses made in the digital era that have been produced with any assistance from Tokina.  Tamron on the other hand, has been involved with several.  I honestly don't know enough about Sigma to say one way or the other.

David M Russell wrote:
All the Nikon G series lenses, in my experience, are ridiculously sharp.

I doubt very seriously that the Tamron is even close.

A good value for the money? Maybe. I can't say. Personally, I don't skimp when it comes to glass.

Fred Greissing wrote:
Tamron is better at 24mm, both similar at 70mm, tamron however is weaker at 50mm

http://www.the-digital-picture.com/Revi … &APIComp=0

I am not questioning whether you are right or wrong, but I do want to point out that, in the link you provided, the lenses weren't tested on the same camera.  They weren't even tested on the same brand.

It isn't possible to say, with certainty, that they would have gotten the same results if both lenses had been tested on the D3X.