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Focus Fast Lenses Stopped Down

Fast lenses (f/1.2, f/1.4, f/2) can be more difficult to focus because of the strong aberrations present wide open, particularly the contrast-reducing haze of spherical aberration. As a result, focus error is always a risk, whether by eye or autofocus or Live View, because in all cases there is “smeared” focus.

A “fast” lens as used here means a lens that on the 35mm format is f/2 or faster, typically f/1.4 or f/1.2. However, even f/2.8 lenses can be affected by spherical aberration, so there is no hard and fast rule. With medium and large formats, a fast lens might mean f/2.8 or f/4, depending on focal length.

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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.

Save yourself those years of trial and error by jump-starting your photographic technical execution when making the image. The best lens or camera is handicapped if the photographer fails to master perfect shot discipline. High-resolution digital cameras are unforgiving of errors, at least if one wants the best possible results.

  • 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.

Canon Ec-S SuperMatte (left) and Ec-D grid screen

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