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

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

holin wrote:

JimKasson wrote:

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

Very true. Imho not that important for simple good copy vs bad copy testing, though.

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.

Interesting. Does the computer also judge focus, i.e. do you have a feedback loop from the camera to the rail controller (via hdmi)? If so, I see the JPEG engine as a potential problem: what if you forget to set the same creative style options like sharpening, etc. each time.. Actually, the JPEG engine is also a problem when eyeballing the focus. Overkill would be to get the RAW from the camera, use that for focusing information and do a simple CDAF search with the rail+controller.

Here is a link to a bunch of test results and descriptions of protocols:

http://blog.kasson.com/?s=loca

Imatest has a utility to find the sharpest file given a ROI, but I rarely use it. Jack Hogan and I have written Matlab code that interfaces with dcraw and MTF Mapper to do the testing.

The focusing is not done in a closed-loop fashion.

Jim

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