[rollei_list] Re: Spinning front taking lens


----- 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 

---
Rollei List

- Post to rollei_list@xxxxxxxxxxxxx

- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe' in the subject field OR by logging into www.freelists.org

- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with 'unsubscribe' in the subject field OR by logging into www.freelists.org

- Online, searchable archives are available at
http://www.freelists.org/archives/rollei_list

Other related posts: