Possible Clues:

• Photographer's concern
• It affects depth of field
• Speed measure
• Camera setting, and what shortened 18-, 24-, 47-, and 58-Across?
• Setting numbered in multiples of the square root of 2
• 35mm setting
• Measure in which 2 is half the size of 1.4
• Shooter's setting peacock about stone
• Photographer's setting, perhaps
• Manual Minolta setting