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Underwater Housings: (continued)
Ports come in
three types:
▪ standard for normal lenses
▪ domes for wide-angle
▪ extended for macro (an extension ring can be
place on a standard to achieve the same effect)
Ports and water magnification:
One of the factors that comes
into play with a housed system (unlike the revered amphibious
Nikonos which had water-corrected lenses) is that a port acts like
a second lens over the primary (the lens attached to the camera).
Consequently the photographer now faces the additional problem of
water magnification.
But that's merely the first of
two magnification factors! The typical APS-sized sensor of most
digital SLRs increases the effective focal length of any lens by
about 1.6X. So in effect a "standard" 50mm effectively becomes an
80mm short telephoto. Now throw in the 25% water magnification
factor and the lens becomes as a 100mm macro lens! |
