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Depth of Field at the Periphery

Consider these actual images of the lens diaphragm of the Zeiss 100mm f/2 Makro-Planar, taken by shooting through the rear of the lens. The actual shape as seen at the sensor might be somewhat different than seen here (camera position as shot is not necessarily at the focal plane, or centered)

As can be seen, at wider apertures the entrance pupil will be reduced in effective diameter, which means a reduced brightness (vignetting) and also more depth of field (smaller f-stop).

This smaller entrance pupil has an important implication: stopping down a lens one stop from wide open may make absolutely no difference to depth of field towards the periphery, because the effective aperture does not change, or changes very little. There may be other beneficial effects (reduction in various aberrations) but with many if not most lenses, no gain in depth of field will be seen at the periphery from wide open to one stop down.

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Diglloyd Making Sharp Images articulates years of best practices and how-to, painstakingly learned over a decade of camera and lens evaluation.

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  • Eases into photographic challenges with an introductory section.
  • Covers aspects of digital sensor technology that relate to getting the best image quality.
  • Technique section discusses every aspect of making a sharp image handheld or on a tripod.
  • 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.

Actual pictures of lens diaphragm at f/2, f/2.8, f/4, f/5.6, f/8
Zeiss 100mm f/2 Makro-Planar

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