D200 w/18-200 - first macro attempt

Started May 9, 2006 | Discussions thread
Peter iNova Veteran Member • Posts: 3,250
Diffraction reaction

Diffraction shows up due to a moving set of variables. Focal length changes cause diffraction noticeability threshold changes. A longer lens will stop down to higher f-numbers with less effect.

Consider the compact cameras. They're showing significant diffraction at wider f-stops. It's not unusual to see more of the effect at f/8 than on a DSLR at f/16 for similar fields of view.

With a zoom, you would have to test various settings to see how much becomes too much for you.

And, as if that weren't enough, the shape of the iris opening can exacerbate--or help--the effect. If that iris were a perfect circle, the effect would be spread out smoothly and possibly less, which is almost never the case, especially at small openings where the iris shape tends to be more faceted.

The effect is a low-impact diffusion, rising to a noticeable sharpness diminishment. But some pictures are better with deeper DOF even though diffraction is demonstrable.

Any declaration that one should ONLY shoot below all possible visible diffraction effects misses other opportunities. Balancing the variables of focal length, iris shape, f-stop, ISO, shutter speed, contrast, sharpening, filtering, lighting and intention of the image to communicate takes consideration and frequent compromises.

Photography isn't an exercise in avoiding all possible negative attributes; it's a juggling workout in service of getting the shot and influencing the viewer to become part of the intended communication.


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