To the Editor:

I am a freelance photographer in addition to my day job as a physical chemist / spectroscopist. As spectroscopy involves the study of interactions between matter and radiation, I can leverage my knowledge of light, optics, detectors and signal processing (especially for low light levels) in photography.

Comments on Ian Shire’s good how-to Nature Article (Easy Wider, March 2008):

“Avoid the polarizer blues” treats the subtle varying blue sky color effect. More subtly note that cameras with autofocus typically use linear polarization to do it and require circular polarized add-on filters in order not to interfere. Other cameras can use linear polarizer add-ons. The circular / linear ‘blues’ effects are similar but somewhat different. If stacking filters, keep the polarizer on the outside or you may get visible stress colorization. (To really see ‘stress,’ look out an airplane plastic window through a polarizer.)

“Maximize depth of field” advocates the smallest aperture, e.g., f/22, “to ensure maximum sharpness throughout the entire scene.” But diffraction effects decrease image sharpness at small apertures. Use the largest ‘smallest’ aperture giving the required depth of field to truly get maximum sharpness. Related to this and to best set focus for hyperfocal distance (“Getting hyper about focusing”), be aware that lens barrel depth of field marks (if your lens has them) are for guidance for “typical” enlargement size. If you print / view larger than about 8”x10” you need to use a smaller aperture than indicated. Maybe that’s why Ian Shire advocated a generic f/22 in the first place.

—Ronald Sheinson
Silver Spring, MD