prism

**optigirl** · 11-04-2008, 10:39 AM

I have never had this come up before and I am hoping all your combined knowledge will help me....I have a patient that is wearing a FT 28 and needs 6D prism base down in OD...he is wearing Fresnel and hates it.....the problem is....he doesn't need prism in the bif ( with the Fresnel I cut the bif area out) ...so surfacing the prism in is not an option....I am wondering if anyone else had this come up....and do you know if we surface the lens with slab off in that eye if it would correct the image displacement at the reading level so he doesn't have to continue with the Fresnel.....Also...he doesn't want 2 pairs of glasses....any in put would be greatly appreciated.... Thanks!!!!

**chip anderson** · 11-04-2008, 10:49 AM

Franklin Bifocal!

**Jacqui** · 11-04-2008, 01:36 PM

Originally Posted by chip anderson

Franklin Bifocal!

Beat me to it again, Chip. :)

**Chris Bowers** · 11-04-2008, 04:09 PM

Yes you can use a "slab like lens" bicentic grind

**Jacqui** · 11-04-2008, 04:31 PM

Originally Posted by Chris Bowers

Yes you can use a "slab like lens" bicentic grind

Yes, but that would require someone that's smarter than the lens

Ain't too many of them left. :( :( :(

**Spazmonkey** · 11-04-2008, 07:08 PM

Did you split the prizm for the ground lenses? Phresnels only require one lens. SHould be 3 bd OD 3 BU OS.

**Spazmonkey** · 11-04-2008, 07:19 PM

Have you tried to split the prizm. Fresnals are only needed for one lens.
Try 3 BD UD, 3 BU OS.

**Jacqui** · 11-05-2008, 11:24 AM

Originally Posted by Spazmonkey

Have you tried to split the prizm. Fresnals are only needed for one lens.
Try 3 BD UD, 3 BU OS.

Some people cannot tolerate split prisms. Sometimes certain conditions also require prism only on one lens.

**Jacqui** · 11-05-2008, 11:25 AM

Has anyone thought of using a freeform on this?? It should be possible, although there will be a blend line.

**Robert Martellaro** · 11-05-2008, 03:25 PM

Originally Posted by optigirl

I have never had this come up before and I am hoping all your combined knowledge will help me....I have a patient that is wearing a FT 28 and needs 6D prism base down in OD...he is wearing Fresnel and hates it.....the problem is....he doesn't need prism in the bif ( with the Fresnel I cut the bif area out) ...so surfacing the prism in is not an option....I am wondering if anyone else had this come up....and do you know if we surface the lens with slab off in that eye if it would correct the image displacement at the reading level so he doesn't have to continue with the Fresnel.....Also...he doesn't want 2 pairs of glasses....any in put would be greatly appreciated.... Thanks!!!!

You can indeed use a slab-off lens to neutralize/modify the distance prescribed prism from the near point, as well as any induced vertical prism imbalance (if any). In this case it would probably be a custom base up slab on the right and/or a reverse slab base down on the left. However, I suspect that this might be one of the rare times when a Franklin (bonded SV) lens would look better than a segmented multifocal if a large amount of distance prism can't be split (rarely the case), as long as the Rx isn't high plus.

**QDO1** · 11-05-2008, 03:40 PM

There are prisim controlled glass bifocals (zeiss), but not to this degree
so you are stuck with

1. 2 pairs
2. Franklin split
3. Fresnel lens
4. slab off

I would personally question the script. Not needing any prism at near, but 6 base down at distance seems very very unusual

**chip anderson** · 11-05-2008, 06:35 PM

If it's bonded, it ain't a Franklin.

**Jacqui** · 11-06-2008, 11:10 AM

Originally Posted by chip anderson

If it's bonded, it ain't a Franklin.

Sure it is :) In my case I have to bond because of insurance regulations, others do it because they were taught to.

**QDO1** · 11-06-2008, 11:59 AM

how to make a franklin split... THE definitive method

Take your Franklin (any old Franklin will do, male Franklins are easier)

turn your Franklin around

Put on your jack boots.

Take aim between the legs

For sure you will get your Franklin to split with the right technique!

**Fezz** · 11-06-2008, 12:12 PM

Originally Posted by QDO1

how to make a franklin split... THE definitive method

Take your Franklin (any old Franklin will do, male Franklins are easier)

turn your Franklin around

Put on your jack boots.

Take aim between the legs

For sure you will get your Franklin to split with the right technique!

So.........do you bond or not?

;):cheers::cheers::cheers::D

**HarryChiling** · 11-06-2008, 12:35 PM

Originally Posted by Fezz

So.........do you bond or not?

;):cheers::cheers::cheers::D

No way then you'd lose your franklin spliting boots.

**Jacqui** · 11-06-2008, 01:37 PM

I thought he was going to mention using a pair of scissors on a large denomination bill.

**HarryChiling** · 11-06-2008, 02:01 PM

Originally Posted by Jacqui

I thought he was going to mention using a pair of scissors on a large denomination bill.

LOL that would have been great.:cheers:

**chip anderson** · 11-06-2008, 02:44 PM

If you bond, it's a home made Executive.

**Jacqui** · 11-06-2008, 03:50 PM

Originally Posted by chip anderson

If you bond, it's a home made Executive.

It's still a Franklin because it's made from two lenses (or sometimes three :) ). Anyway George Washington's, made by Franklin, used balsam pitch (crude bifocal cement) to bond them.

**chip anderson** · 11-06-2008, 05:56 PM

Actually Canadian Balsam isn't a crude cement. I have seen it used up to the '70's and possibly the '80's for wafer segments. They stayed on forever and worked very well. Still used as a cement in some compound telescope lenses. Can be removed with Xylenes only.

Forgot to mention it is still used a lot to cement covers on slides for pathologists.

Chip