shaocaholica
Well-known member
Great technical writeup here about the lens:
http://www.dyxum.com/columns/articles/lenses/SAL-135F28/Sony-AF-135-STF-SAL-135F28_review.asp
Long story short, its a 135/2.8 portrait lens designed by Minolta back in 1999. Despite being over 10 years old, its still one of the newest and most radical 135mm optical designs around to date. What makes it special is that is has a special glass element at its optical axis that no other lens lens. Its called an apodization element which won't mean much to most people. Its essentially a variable thickness ND filter which blocks less light at the center and becomes darker towards the edges. The diagram in the above article does a pretty good job describing this part. So whats so special about having this? Well, it doesn't actually vignette the image as most people think. What it does is soften the out of focus "bokeh" edges so that instead of "hard" circles in the bokeh you get soft circles. So soft that its like a Gaussian distribution almost. This element also eats up light which is why this lens is a T/4.5. Check out the sample images online for this effect.
So whats the deal with the 2 apertures? Its not that fancy really. The rear aperture is controlled by the camera. The front aperture is fully manual and is designed to be circular at all click stops but only has 3 click stops and only closes down to T/6.7. Only one aperture is ever activated at a time. The inactive aperture is always full open.
I actually have one of these but its going on ebay soon as its burning a hole in my wallet.
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