Tamron 60mm F2 Macro concerns

Started May 28, 2012 | Discussions thread
Senior MemberPosts: 1,625
Re: Tamron 60mm F2 Macro concerns
In reply to siejones, May 28, 2012

siejones wrote:

I am 90% sold on the 60mm and I have seen a half decent price on a mint one used one but diffraction is the biggest concern for me and mainly this review that amplified my concerns:


(read the conclusion)

I think if I can get over that then I will pull the trigger.

In general, the brand/type of lens should make no difference at all when it comes to the amount of diffraction softening that occurs at any given f-number. That's a matter concerning the physics of light, and shouldn't vary from lens to lens.

Of course, if the lens is extremely sharp, you may be able to discern the effects of diffraction at lower f-numbers (larger apertures) than you'd be able to with a lens that's not quite as sharp. And cameras with higher pixel density (higher resolution) will also allow you to begin seeing diffraction effects at lower f-numbers than you would with a lower resolution camera (although the diffraction of the light itself has nothing whatsoever to do with the pixel density of the camera).

Now, having said all that, there does appear to be something going on with the aperture mechanism of the Tamron 60mm macro, in which the aperture diaphragm may be closing down by more (or perhaps less) than it's supposed to at a given indicated f-number. The Kurt Munger review suggests that his copy of the Tamron might be stopping down to a smaller aperture than it should be (for example, f/16 at an indicated f/11, or f/22 at an indicated f/16), indicating a calibration problem that might or might not be fixable by a trip to the Tamron service center.

Evidence for the above is provided by a couple of reviews of the same lens on the Photozone.de website. The Canon version of the lens (tested on a 15MP EOS 50D), showed diffraction kicking in at fairly low f-numbers (pretty typical performance), with the measured resolution at f/22 being less than 1200 lp/mm. Meanwhile, the Nikon version, tested on a 10MP D200, showed a measured resolution of over 1700 lp/mm at f/22. The reviewer pointed out the likelihood of a calibration problem (larger physical aperture than indicated by the f/number), as this was way more resolution than one normally would expect from a lens set at f/22. This is exactly the opposite of the behavior that Kurt Munger described for his copy of the same lens (which, of course, was the Sony/Minolta-mount version of the lens -- but that may not be a significant factor).

Here are the links to the two photozone reviews referred to above ...



The bottom line is that no lens should be any more affected by diffraction at any given f/number than any other lens. But calibration issues, which result in a larger or smaller physical apertures than would be correct for a given f/number (and which, therefore, also affect the DOF being achieved at that indicated f/number) can have a very significant effect.

I'm not sure whether any of the above helps you in making your lens decision, but hopefully the extra info was helpful in some way.



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