EXCERPT page containing first few paragraphs. 2024-04-20 08:08:20
UA_SEARCH_BOT_compatible_botmozilla/5.0 applewebkit/537.36 (khtml, like gecko; compatible; claudebot/1.0; +claudebot@anthropic.com) @ 18.116.63.236
For full access, subscribe here. Or click title to login. 
Focus Targets
To test for focus error, a good target is needed. A target can be just about anything, but must have good contrast for the camera to focus on, and must have fine detail on the target as well as behind it and in front of it, so that you can assess the results.
Confirming focus accuracy in the field
Don’t get carried away with “lab” targets; these invariably involve close distance shooting, and your camera and lens might behave differently at greater distances. Always cross-check and verify your tests.
When I’m wondering about focus accuracy with a lens, I’ll take a walk around the neighborhood or city, and shoot a variety of subjects that work well as targets (at a wide aperture). This necessary and real-world confirmation will give you the confidence of knowing (or not) that focus can be relied upon.
Article continues for subscribers...
Diglloyd Making Sharp Images is by yearly subscription. Subscribe now for about 13 cents a day ($50/year).
BEST DEAL: get full access to ALL 8 PUBLICATIONS for only about 75 cents a day!
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.
