Saturday, April 1, 2017

Sony Diaries #994: (The magic of) Micro Adjust

There's nothing more frustrating than a heretofore sharp lens that's not quite all there on a different body. It's also frustrating that a lens that should be sharp is unsharp to varying degrees on different bodies. Since the bulk of my lenses are legacy lenses (Minolta AF) that are 20-30 years old, I started to doubt my skills as an informed buyer on Kijiji and Craigslist. At one point, I just thought my eyes were starting to deceive me.
On my first wedding of the season, the shots on my Tamron 28-75F2.8 were not as sharp on my second a99 body as it was on my first a99 body. Was it time to junk this lens? 
A few weeks ago, I was so lucky to find a Minolta 50F1.4 AF on Kijiji. A cursory check on my a99 showed a sharp lens at f2.8, some CA, and  generally low contrast. CA and contrast can be remedied in post (or even in-camera) but sharpness can't be (clarity sliders and unsharp masks are akin to putting on cologne without taking a shower first).
The price was irresistible ($100 versus $550 for a Sony 50F1.4, $1150 for a Sigma 50F1.4ART). Plus it's rare for a Minolta 50F1.4 to come on the local market. At the very least, the F1.4 means faster focusing in low light, even if the taking aperture would be at 2.8.
I come home and the lens turns out to be even more unsharp on my a77II than it is on the a99.  I love shooting wide-open for shallow depth-of-field but shallow DOF will reveal focusing errors. A lens may focus precisely but not necessarily accurately. A lens may focus a mm or more forward, or backward. A shallow DOF will reveal this right away. I want precision and accuracy. Even on a cheap lens. Then I remembered the idea of micro adjusting lenses. 
Micro adjustment allows us to make a correction for every lens when paired with any camera body so that a compensation is automatically applied; compensation will vary depending on the camera body used.
To jump to my conclusion, my $100 Minolta 50F1.4 is razor-sharp at F1.4, on the spot/plane that I focus on. On the following photos, I focused on "9902". Taken with the same lens on 2 bodies, APS-C and Full Frame.
1/100@F1.4, Sony A77II.  Compensation: -20 (yikes!)
1/100@F1.4, Sony A99.  Compensation: -8 (huge difference with the A77II's -20).
My methodology, adapted from several sources available online,  will be up on a future blog post. Micro adjustment is only available on some, not all, of the newer cameras. the Sony a99 was introduced about 5 years ago. I have since micro adjusted all my lenses which has led to a major difference in sharpness. Micro adjustment is particularly important with fast lenses and macro lenses (slow lenses but typically shot wide-open and very close to the subject resulting in very shallow DOF).

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