Help judging performance of my FE55z, FE35f2.8z horizon/infinity

Started Jul 5, 2016 | Questions thread
JimKasson
JimKasson Forum Pro • Posts: 26,613
Focusing
1

holin wrote:

JimKasson wrote:

Most people's difficulty in getting good MTF Mapper numbers is, I believe, the result of several issues:

  • Alignment
  • Getting a high-resolution target
  • Alignment
  • Getting the target big enough.
  • Alignment
  • Getting the target far enough away
  • Alignment
  • Lighting the target properly
  • Alignment
  • Vibration
  • Alignment
  • Field curvature

Oh, and alignment is important, too.

I would like to add flat target the above list. Folded and then straightened newspaper taped to a wall from two corners is not quite there. And alignment.

Oh, I forgot a biggie: focusing accuracy and repeatability. After some truly eye-opening experiments, I now do my numerical slanted edge testing using a computer-controlled focusing rail to find the best focus position. When I was focusing by hand, I was getting unacceptable focusing errors with made the tests irreproducable and unrepeatable.

Thinking about it, this is probably number two after alignment.

Using AF with a good target is usually, but not always, more repeatable than MF, but AF can produce systematic errors in the presence of lens longitudinal chromatic aberration on a7x cameras.

The combination of field curvature and focus errors can lead to quite misleading results.

Jim

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Nikon D5 Sony a7 III Nikon Z7 Fujifilm GFX 100 Sony a7R IV +4 more
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