Wednesday, April 5, 2017

Sony Diaries #997: micro adjusting a Minolta 35-105F3.5-4.5: A Methodology

I recently purchased a Minolta 35-105F3.5-4.5 lens through Kijiji, in very good condition, clean elements, no grease on the aperture blades, very few markings, for $40CDN. It's a typical Minolta with an all metal body, built like a tank. I don't know when this older version was released but I do know the new version was released in 1988. This would make this lens at least 30 years old. Zooming is still silky smooth, with just a touch of stiffness to prevent zoom creep. I will have to go out and take some pics, fully expecting pics with the legendary Minolta colours and here too: an unquantifiable creamy bias toward the warm side, soft-ish micro contrast without sacrificing overall sharpness.
As a relatively slow zoom lens (F3.5 at wide and F4.5 at tele), micro adjustment is not a critical issue but I still wanted to be in the immediate vicinity of accurate focus. The default  on the camera (for any lens) is at +/-0. Below is my test subject, chosen for it's intricate details.
Not knowing where to start, I used the whole range on my camera: -20 to +20. 1/100 F4.5 ISO2000.
Without a doubt, micro adjust -5 is the sharpest in the set. I shot 3 more frames in the neighbourhood of -5.
The sharpest is towards -3 so I'll set the camera at -4. At f4.5, the DOF is not shallow at all but -4 puts me as close to the middle as possible. Below are the final shots with micro adjust -4, taken at both 35mmF3.5 and 105F4.5, all at their respective minimum focusing distance (MFD).
Micro adjust is not of much use with slower lenses, particularly when they are used for more than the MFD... DOF is not a concern. In the case of the Minolta 35-105F3.5-4.5, I determined the micro adjust to be -4... not that far from the default setting 0.0.
I'm open to suggestions as to how I may improve on my methodology. All in all, not bad for a $40 lens.

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).