[rollei_list] Re: Spinning front taking lens
- From: Peter J Nebergall <iusar4s@xxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 29 Dec 2005 17:18:12 -0600
I had an old Russian dog&^%%$ piece, and the front-element was loose in
the barrel. It spun, but it was clear to me it spun cuz it was not too
well made. Had an Isco 135 4.5 manual in M42 mount that did it, for same
reason...
P.J. Nebergall
On Thu, 29 Dec 2005 14:56:18 -0800 "Richard Knoppow"
<dickburk@xxxxxxxxxxxxx> writes:
>
> ----- Original Message -----
> From: "Jim Brick" <jim@xxxxxxxxx>
> To: <rollei_list@xxxxxxxxxxxxx>
> Sent: Thursday, December 29, 2005 9:33 AM
> Subject: [rollei_list] Re: Spinning front taking lens
>
>
> > I'm not sure that I understand this lens spinning
> > property.
> >
> > I have always been told that in lenses that consist of
> > more than one element, each element has a specific
> > orientation with the other elements in the group. I was
> > told that if I took a lens apart, I should mark each
> > elements orientation so that it could be reassembled with
> > each element oriented properly with respect to the other
> > elements.
> >
> > So a spinning element makes no sense to me.
> >
> > ??
> >
> > Jim
>
> This isn't true. Spacing can be critical but rotational
> position is not. Lenses are very precisely centered when
> manufactured. This is done by placing the polished lens
> element on the end of a rotating tube covered with something
> like pitch as a lap. A point of light from a collimator is
> shown on the lens and the reflections from both sides viewed
> in a telescope. The lens is pushed around on the lap while
> rotating until the images of the point are stationary. The
> lens is then clamped on the top by a second tube and the
> edges ground precisely parallel and concentric with the
> optical axis. A variation of this method is used to
> precisely center cemented elements. The current technique is
> to optically center each element as it is cemented and then
> grind the edges of the assembly. An earlier method was to
> very precisely center and grind each element and clamp the
> edges for assembly. The optical method elimates some of the
> accumulated error possible with the older method.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
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