John Gaasland wrote:
>
> 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.
Whoops, NO. You'll need more like 40 or more for the normal lens. I was
referring to the 50/3.5 and 50/2 macros, which supply 25mm of extra
extension themselves, using the helicoil. See 'timberwolfs' recent post
for another explanation.
--
george :>)
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