Prism segs

[drk]

Hey, I know the crafty amongst you can fabricate a prism seg. Have you ever fabricated a "prism trifocal"?

I was reading a post on another site about a stroke victim who has an exodeviation worse on upgaze and better on downgaze. Can you, practically speaking, cut three lenses and mount it in a frame?

(BTW, how do you cut lenses, anyway?)

Hats off to the optical experts on this board.

[chip anderson]

Yes you can make a "Franklin" trifocal, same proceedure as Franklin bifocal except you have to be more carefull. Be sure and charge a bunch, you gonna earn it. With this many pieces in the frame you will need to cement the sections together, it's dicey enough getting two pieces to stay in the frame.


Chip

[Jacqui]

Have to agree with Chip. Just be incredibaly careful positioning the parts, and use a good adhesive between sections.

Jacqui

P.S. Have fun (?)

[chip anderson]

Actually, I would make the distance and intermediate first, cement, then do the add and cement.

Chip

[chip anderson]

For how to cut see earlier posts on Franklin bifocals. I use a cable drill and a table disc sander, followed by rough to smooth files for the real fine work.

Chip

[Jacqui]

The last pair that I made, I used a jeweler's saw with a fine blade to cut and progressively finer sanding disks at slow speed to smooth. Just be careful and take all the time you need.

[drk]

Thanks for the input. It's a theoretical case for me. I'm going to refer the Dr. on the other site to this thread.

[hcjilson]

If anyone has occasion to do one of these either bi or trifocal- please use your digital camera at each stage.Along with a description of what is being done, and why. It would make a great thread.

In a carreer that began 44 years ago this month, I have yet to see a Franklin in the flesh or in a picture. After some checking around with a few peers, I find I am not alone. I'd love to see it done.

hj

[Texas Ranger]

hj, I see a lot of pilots, being near DFW airport. several years ago, I had a pilot who just had to have a top seg exec, but the standard seg seperation and add ratios were unsuitable and the double seg blanks were waayy to small. so we di an exec bifocal, and created two patterns, one for the exec. bifocal, that was the distance and near rxs, then another pattern for the top seg, which was a single vision lens of the rx for the desired focal length; ran both lens a size large, then fined down the edges to be bonded together on a flat lapidary type wheel on 400 grit paper; this work quite well, but was quite expensive, the pilot was thrilled...

[chip anderson]

H.C.

I will answer your prayers in a few days. I did take digital pics. on my last one, just haven't gotten around to writing the narative.

Chip