Attention Tamron 24-70 VC owners

Started Jul 28, 2012 | Discussions thread
gl2k Veteran Member • Posts: 3,232
Re: Problem #2: Aperture lever miscalibration

Horshack wrote:

Some more testing and I quickly realized that there is a 0 stop EV difference between f/2.8 and f/4.0 on my copy, whereas obviously there should be a 1 stop EV difference (or somewhere close to 1EV after accounting for T-stop variability). This EV delta was measured in the center (discounts any vignetting) and was measured on two separate bodies (discounts bent/misaligned aperture lever on the body). It's clear the aperture lever on the lens is miscalibrated; I confirmed this by measuring not only EV but also DOF. I see hardly no DOF difference between f/2.8 and f/4.0, whereas I see the expected difference between f/4.0 and f/5.6.

I have the exact same problem on my 17-50 DX mm Tamron.
And a similar problem on my 90mm macro Tamron.
Very interesting.

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