Does anyone know what the optimum aperture is for this lens? A old product brochure suggests that it is close to the maximum 4.5 aperture. This is contrary to the usual "two stops down" rule. I don't really have the facilities or the time right now to do any valid testing, so I'm hoping that someone has already found the answer. Thanks in advance.

-- Ian Binnie (iab@blakes.ca), April 17, 2000

Answers

The latest Photo Techniques (May/Jun 2000, Vol 21 No 3) takes an interesting look at the 'two stops down' myth. Howard Bond has a very enlightening (and somewhat depressing) article called 'Resolution Loss to Diffraction'. A lens with a larger maximum aperture may need 5 stops down and one with a larger max aperture (say f9) may only need 0 or 1. The article is worth a read.

-- Richard Rankin (rpr@coolabah.com), April 17, 2000.

Sorry about that:

A lens with a larger maximum aperture may need 5 stops down and one with a **smaller** max aperture (say f9) may only need 0 or 1.

-- Richard Rankin (rpr@coolabah.com), April 17, 2000.