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

Started Jul 5, 2016 | Questions thread
l_d_allan
l_d_allan Veteran Member • Posts: 5,087
Easy to do invalid brick wall testing, but not beyond many motivated Zony owners.

Nephi wrote:

As others have noted the brick wall test is very hard to do correctly.

As is all valid "good copy vs bad copy" testing for those not owning an optical bench or commercial ImaTest setup. (but I'm hoping to be yet again in error and that the OOF LED approach works out)

Even the slightest lack of a being parallel and you will get skewed results.

My experience has been that:

  • with sufficient attention to detail,
  • after a learning curve,
  • a motivated purchaser of a pricey Sony/Zony lens ... especially those with known crap-shot q/c issues ... (term from LensRentals that applies to FE90, several zooms, and especially the notious FE35 f1.4 ... ten of ten which were rejects)
  • should be able to accomplish adequate alignment with a brick wall
  • at a rigor level appropriate for "good copy vs bad copy" testing.
  • But NOT for valid, repeat-able MtfMapper numbers (bummer)
  • ...
  • Obviously ... GIGO ... but you don't need 100% alignment down to to the micrometer to get adequate alignment. You can be the slightest bit off, but obviously past a certain threshold, evaluation will be invalid. 
  • I don't happen to know precisely what that percentage is, but I don't think you need to be a rocket scientist at JPL to achieve satisfactory alignment. YMMV.

Not to mention a slight difference in the way the light hits the wall can cause sharpness differences.

Along with multiple other issues ... especially sloppy focus. I'll speculate that testers who have trouble with meticulous alignment might also have trouble with meticulous focus.

Personally, I would only use the brick wall test to check for gross decentering

Sorry to be blunt, but perhaps that says more about your testing proficiency than the adequacy of brick wall testing ... done correctly?

I've got my fingers crossed that the relatively simple, but still unproven OOF LED test is satisfactory to weed out the great majority of out-of-spec lenses.

One of the "known unknowns" is how much of these out-of-spec issues are from de-centering. I've got an email to Roger C. at LR to check whether he might have an estimate he could share.

In the meantime, I'd be reluctant to purchase ANY FE lens if you aren't confident in your experience and expertise to do "good copy vs bad copy" testing.

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