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EXCERPT page containing first few paragraphs. 2023-03-25 12:36:45

Violet Fringing Case Study (LOCA with Zeiss Otus vs Others)

Here we have lens torture-test study of violet fringing (“purple fringing”) with four normal lenses across the aperture range. That violet halo is a color aberration caused by longitudinal (axial) chromatic aberration (LOCA). LOCA affects the entire frame, including the center.

In an otherwise well corrected lens, LOCA is usually the primary factor in reducing contrast at wider apertures, also influencing the point spread function by adding a diffused colored halo around high contrast transitions, even if other aberrations are well controlled*. Such effects improve rapidly with stopping down, so the measure of top-grade lens is how well it controls that that color halo at full aperture and one one or two stops down.

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  • Covers aspects of digital sensor technology that relate to getting the best image quality.
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  • Depth of field and how to bypass depth of field limitations via focus stacking.
  • Optical aberrations: what they are, what they look like, and what to do about them.
  • MTF, field curvature, focus shift: insight into the limitations of lab tests and why imaging performance is far more complex than it appears.
  • Optical aberrations: what they are, what they look like, and what to do about them.
  • How to test a lens for a “bad sample”.

Intrigued? See Focusing Zeiss DSLR Lenses For Peak Performance, PART ONE: The Challenges, or (one topic of many) field curvature.

Zeiss ZF.2 Otus 55mm f/1.4 APO-Distagon
Zeiss ZF.2 50mm f/2 Makro-Planar
Canon EF 50mm f/1.2L
Canon EF 50mm f/1.4

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