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EXCERPT page containing first few paragraphs. 2023-06-02 12:46:48

Optics (MTF)

The graphs shown below are a type of MTF (Modulation Transfer Function) graph, showing MTF about the geometrically best focus point (e.g., the tightest cluster of image-forming rays).

Note that “best focus” isn’t necessarily the same for fine detail (40 line pairs/mm) as for coarse detail (10 lp/mm), and this further complicates focusing for critical work.

Stopping down from f/1.4 to f/4 increases MTF (contrast) substantially, especially for fine detail, and also increases the depth of field, but notice how peak performance at f/4 is no longer centered about the focus point; the zone of focus has shifted!

The net effect (in the general case) is a lower contrast result where maximum sharpness is expected, and possibly unwanted sharpness elsewhere (usually in the background).

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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.

Graph 1a

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