Pentax Quality Control Strikes Again

Started Apr 23, 2015 | Discussions thread
OP Joseph Tainter Forum Pro • Posts: 11,004
Re: Pentax Quality Control Strikes Again

Timbukto wrote:

I would suggest you do MFA tuning prior to brick wall tests. This is because if the lens is front focusing, it is possible that due to field curvature, some portions are within sharper focus than others. No lens in existence exhibits absolute perfect flat plane field curvature, but by not calibrating it first you may be seeing the tail end of your field of focus instead of the middle portion, etc.

Likewise my 18-55 by default looks to have soft portions in some areas and not others, but with MFA tuned, it can give me a sharp frame to frame 18mm f3.5 shot.

See here -

http://www.lensrentals.com/blog/2015/03/a-quick-zoom-variation-demonstration

Thanks for the recommendation, but this wouldn't account for unbalanced weakness. That can only come from defective assembly.

I've done this test on many lenses before testing for focus compensation. Nearly all have subsequently needed some degree of focus compensation adjustment.

Joe

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