on 2/20/04 9:07 AM, Piers Hemy at piers@xxxxxxxx wrote:
>
>
> Regarding the amount of extension, I seem to remember calculating that one
> needs around 45mm to go from a 90mm 1:2 to a 90mm 1:1 ; in other words, all
> three olympus auto tubes (25+12+7 = 44mm). Or is that wrong?
>
> Roger Key
Roger - to get 1:1 with a 90mm lens you need -total- extension of 45mm (not
allowing for telephoto effects). This extension comes from the extension
tube *and* the existing lens helical focusing... just the lens alone gives
1:2 which implies about 23mm of focusing extension, then a 25mm
(approximately) tube is added and you start over again from infinity (0mm
extension) on the lens' extension. When fully racked out you have about 45mm
total extension.
--
Jim Brokaw
OM-'s of all sorts, and no OM-oney...
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