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Thread: Free form Bifocal/ Digital Slab Off?

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    Free form Bifocal/ Digital Slab Off?

    Couple questions:

    First: Are there digital bifocals? if yes how is the segment applied using free form tech?


    Second: Can you apply slab off using free form tech?
    Last edited by Keinsohn03; 12-30-2022 at 04:07 PM. Reason: typo

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    Quote Originally Posted by Keinsohn03 View Post
    Couple questions:

    First: Are there digital bifocals? if yes how is the segment applied using free form tech?
    Yes. If you are talking about lined bifocals, the fronts are molded(just like standard bifocals) and the backs are freeform.
    There are freeform round segs(I don't know why) all done on the back with a fuzzy blend zone around the seg.

    Quote Originally Posted by Keinsohn03 View Post
    Second: Can you apply slab off using free form tech?
    Yes, I hate them. It's not a sharp slab line. It's a couple mm wide fuzzy line. I personally think they are terrible, but they are fast and cheap compared to the traditional.

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    Quote Originally Posted by Kwill212 View Post
    Yes. If you are talking about lined bifocals, the fronts are molded(just like standard bifocals) and the backs are freeform.
    There are freeform round segs(I don't know why) all done on the back with a fuzzy blend zone around the seg.



    Yes, I hate them. It's not a sharp slab line. It's a couple mm wide fuzzy line. I personally think they are terrible, but they are fast and cheap compared to the traditional.
    I am talking about a lined bifocal thank you! So how would this process work if it's using both free form and conventional methods to make it? Do you surface the back first with CNC and then surface the front? (I have no current lab experience but am doing a project and having trouble finding a simple step by step guide to all this)

    Is the slab applied during the surfacing phase?

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    Currently there is no way to create a lined bifocal using a free form generator. A salad off is not something that is applied to the lens. Traditional slab off is created by cementing a slab of material to a lens. Grind a prism on the slab until half of the slab is ground off and then the other half is removed hence the name slab off. Tou now have lens with two centers on the same surface. You can also purchase a plastic lens with the slab cast on the lens the mold used is created the same way as described.

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    Quote Originally Posted by Lensman11 View Post
    Currently there is no way to create a lined bifocal using a free form generator. A salad off is not something that is applied to the lens. Traditional slab off is created by cementing a slab of material to a lens. Grind a prism on the slab until half of the slab is ground off and then the other half is removed hence the name slab off. Tou now have lens with two centers on the same surface. You can also purchase a plastic lens with the slab cast on the lens the mold used is created the same way as described.

    So I've seen online that there are companies that can do free form bifocals but I don't understand what that means then if you can't generate a line.


    I also know free form slab off is a thing but then how is that done?

    you explained how both couldn't be but then didn't explain the process.

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    Free form bifocals that are advertised are rd segment on the concave surface. The periphery of the segment is not sharp as is the norm with bifocals except for blended bifocals. You cannot make sharp line with the freeform process that is why you can create a progressive as no sharp lines are wanted. A bicentric grind giving two optical centers on the same lens can be done but once again you will not have a sharp line like a traditional slab off.

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    Quote Originally Posted by Lensman11 View Post
    Free from bifocals that are advertised are rd segment on the concave surface. The periphery of the segment is not sharp as is the norm with bifocals except for blended bifocals. You cannot make sharp line with the freeform process that is why you can create a progressive as no sharp lines are wanted. A bicentric grind giving two optical centers on the same lens can be done but once again you will not have a sharp line like a traditional slab off.
    thank you and both are accomplished during surfacing?

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    Round free-form segments are an option for presbyopic sunglass wearers who don't like PALs...the back-side nature of them allow for mirrors on the front, too...

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    Quote Originally Posted by Keinsohn03 View Post
    So I've seen online that there are companies that can do free form bifocals but I don't understand what that means then if you can't generate a line.

    A blank with a the segment molded on the front(just like a non freeform bifocal) has a free form back surface applied to it.

    What kind of "project" are you working on?

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    Quote Originally Posted by Kwill212 View Post
    A blank with a the segment molded on the front(just like a non freeform bifocal) has a free form back surface applied to it.

    What kind of "project" are you working on?
    I have a 60slide PPT on the topic of todays tech in the making of optical lenses with a forward focus on free form lenses. I have to mention if you can make a free form bifocal, and can you apply slab off using free form tech.

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    Quote Originally Posted by Keinsohn03 View Post
    I have a 60slide PPT on the topic of todays tech in the making of optical lenses with a forward focus on free form lenses. I have to mention if you can make a free form bifocal, and can you apply slab off using free form tech.
    lol. So you have to give a presentation about something you don't understand? Sounds like fun.

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    Quote Originally Posted by Kwill212 View Post
    lol. So you have to give a presentation about something you don't understand? Sounds like fun.
    Yeah it's for class. We haven't learned how to make lenses yet. But doing my own research will hopefully help me understand more when I get into the lab

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    Kudos 03 for working ahead of the curve! Keep that attitude through life, it will take you far!

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