gma wrote:
>
> Pauls0627@xxxxxxx wrote:
>
> > In a message dated 9/17/98 3:09:59 AM Eastern Daylight Time, gma@xxxxxxxxxx
> > writes:
> >
> > << Rule of thumb: Length of tube for 1:1 = half the focal length of the
> > lens, if the lens goes to 1:2 by itself. Eg for the 50 macros, 25 tube
> > does it. For the 90, 45 mm tube needed. (or 25+14+7) >>
> >
> > Correct me if I'm wrong, but I believe that for 1:1 the total extension must
> > equal the focal length. So for the 50mm macros, which have 25mm of extension
> > with the helicoid, you need to add 25mm extension to get 1:1. Using George's
> > other example, then the 90 must have 45mm of helicoid travel (I don't know
> > for
> > sure if it does or not).
> >
> > Paul Schings
> > Coventry, RI
> >
>
> Paul;
>
> It does. It goes to 1:2 on it's own.
>
> george
>
Thanks all for the extension ring info. So, I think that means I need a
25mm for my 50/1.8? Do they make 12 or 13s so you can get 1:2, or put
the together to get 1:1? Thanks, John.
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