"Stephen M. Dunn" <stephen@stevedunn.ca> wrote in message

news:HLn1DD.4qD@stevedunn.ca...

> In article <9j7umvohsljrjsaq7u9gn5808tj84dbk2b@4ax.com>

slingbladeNOSPAM4ME@eudoramailNEVERSPAM.com writes:

>> $In other words, if you are using a 50mm/f1.4 lens, it will be have

>> $like a 100mm/f4.0. If it's slower than f1.4, it'll be even slower

>> $than f4.0 with the 2x.

> There are three stops between 1.4 and 4. An f/1.4 lens with a 2x

> TC has an effective aperture of f/2.8; an f/2 lens with a 2x TC has

> an effective aperture of f/4.

Well, almost.....;-)

A 2X converter does generally "rob" 2 stops from the lens it is used

with - unless the lens is much faster than about f2. Since converters

have a maximum "speed", lenses faster than about f2 mounted on

2X converters act as if the lenses are about f2, giving you about f4

with an f1.4 lens mounted and used wide-open. This can result

in metering exposure errors with lenses faster than about f2 mounted

on converters (unless stop-down TTL metering is used).

--

David Ruether

d_ruether@hotmail.com

http://www.David-Ruether-Photography.com