[rollei_list] Re: Spinning front taking lens

  • From: Don Williams <dwilli10@xxxxxxxxxxxxx>
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Thu, 29 Dec 2005 10:36:41 -0800

At 09:33 AM 12/29/2005 -0800, Jim Brick wrote:

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.

Maybe the orientation you have in mind is front vs back for the elements.

The curvature on the "true" front is generally different from that of the "true" back. Even though I know this, when I recently cleaned a projector lens, I thought I would remember the direction each element belonged, so I didn't mark the elements, which were free-floating, with plastic spacer rings in between them. There were only 3 elements in the lens but the front-to-back orientation of a couple of them wasn't obvious by inspection so I had to try various combinations until the lens presented a good image.

Actually, due to the design of this lens, once the screw ring was removed the elements could tumble as the came out, so maybe that's why I didn't mark them.

Don Williams
La Jolla, CA

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