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.

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