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Sigma 10-20mm f3.5 EX DC on a Sony A7

Sigma 10-20mm f3.5 EX DC on a Sony A7

Posted by / 2nd March 2018 / Categories: cabril, camera and lens / 0 Comments

When I was looking at cashing in my trusty Pentax dslr cameras and buying one of these new fangled Sony A7 things I spent some time searching the interweb for a usable ultra/super wide angle lens. I already had a Sigma 10-20mm (on a PK mount) but didn’t know if this crop sensor lens would be any good. After much ebay activity, frustration, crushing disappointment and a small amount of attempted fraud (not on my part I hasten to add) I sold nearly all of my equipment apart from the Sigma. So I ponied up for the appropriate adapter (in this case the Fotodiox PK to NEX with¬†aperture control!) and carefully shoved it onto the front of my (nearly) brand new Sony.

The first few shots were terrible. Huge vignetting, smeary corners, terrible contrast and a small feeling of self loathing for selling my perfectly functional Pentax.

But after some extremely accurate, scientifically based guessing I found some okay images in amongst the ruins…


As you can see, stopped down the corners have some smearing but focus is pretty good from foreground to the horizon. The colours tend to be washed out and contrast is low in difficult light. Wide open the colours and contrast are better.

I think the sweet spot as far as focal length goes is between 14 and 17mm. The vignetting gets horrible beyond those points and below 14mm the distortion looks like you’re slipping into a time vortex.



Here’s a before and after lightroom. This is at 15mm at f22 to get the best sunstars available on this lens. There is always some cropping to be done but in these middle focal lengths it is pretty sharp and easy to remove.



Overall I think the results are okay. The downsides are lack of specific aperture control (the Fotodiox is well made in my opinion but the aperture ring has no clicks or marks so it’s a bit of guess for anything that isn’t wide open or closed up). Focus to infinity seems fine but the corners do get a bit more smeary than on the Pentax (they were never crystal).

In conclusion: I love the Sony A7 for many reasons, mostly when using it with lightweight, vintage lenses (such as the Asahi Pentax 28mm/f2.8 and the 50mm/f1.7) which I will get into in a later post. I think I will keep hold of the Sigma until I can afford to try something smaller and lighter (see Phillip Reeves’s blog for lots of great ideas). Also: less lens weight in your bag means more room for chocolate muffins, especially good in emergency ‘hangry’ situations…