The aperture is not fully open at f/2.8, allowing a little less light into the camera than it could. For some strange reason, after about a year of owning the lens, dust started to build up inside, even though I had used caps on both sides when not in use. I'm not sure what's causing this, but it's an issue I haven't had with any of the other four lenses I've bought for my X-mount camera. In terms of macro performance, the magnification is about as advertised. When used with extension tubes, the picture can still hold up well.
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