Inaccourate specifications on lenses

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Just a little thought;

Sigma's 2*Teleconverter is in fact closer to a 1.95 teleconverter no full 2*TC (something you only notice when compared side by side with another 2*TC)

Several of sigma's 500mm zoom lenses (eg 150-500mm) are often reported as being closer to 450mm instead of the full 500mm

Tamrons 90mm f2.8 macro lens is in apparently really an f3 lens



Those are 3 such cases I've heard/encountered, but I'm curious as to other examples; and not just from 3rd party as I'm sure if they are "getting away" with such then the "big boys" on the field (eg canon and nikon) are probably using similar title and marketing tactics.

This is purely out of interest I'm not trying at all to say anything about the quality or reliability of 3rd party or 1st party gear (got 2 great 3rdparty lenses and I'd only swap one to upgrade it to the OS version).
 
From what I've heard, the actual accuracy of a lens's specs are not nearly as as close as we would think (or hope for). And this goes for Canon & Nikon, as well as the 'lesser' brands. Besides focal length, there is the aperture size. We might think we're getting F2.8, but it might actually be F2.93...or something like that.

I'm sure that somewhere, someone is testing these things accurately (Maybe DXO).
 
One factor that affects the effective focal length, is focal point distance.

For example Nikon's 18-200 mm superzoom, when zoomed to 200 mm but focused at it's near limit is only giving 135 mm of magnification. The effective focus length increases as focal distance is increased.
 
Pretty common really. Lenses are allowed a 10 percent focal length variability as I understand it, according to the Japan Camera Institute, I believe it used to be called; you know, the organization that came up with that little oval PASSED sticker thing...I think now it's it called CIPA or something like that.

And yes, focal lengths and apertures quite often do vary from the stated specification. Many zooms, and primes, vary from their stated lengths. A 50mm lens that is actually 51.5mm for example, is common. So common in fact that DOF Master has a 51.5mm lens listed...
 
Several of sigma's 500mm zoom lenses (eg 150-500mm) are often reported as being closer to 450mm instead of the full 500mm

Yes... about 450mm... at infinity focus. And, while not relevant to the topic at hand, they're often only about 385mm up close.


The Sigma 120-300mm f/2.8 is often mentioned as well. It's about 280mm at infinity focus... and not a true f/2.8, obviously.
 

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