How come there aren't any other 4 zone progressives like the Definity on the market?
How come there aren't any other 4 zone progressives like the Definity on the market?
No other marketing team thought it was worthwhile?
UnlikelyOriginally Posted by Craig
Quite a few PAL designs have similar power profiles, where the the Add power ramps up and then decreases in power, instead of staying the same or sometimes increasing over the specified power. This so called 4th zone is unuasble though because it exists well below where the eye can turn to be effective, or useful in some way. I suspect the lens designers are trying to reduce unwanted surface astigmatism, and the marketing dept. is trying to sell lenses. Pay more attention to the lens designers.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
What is the number of effective mm the eye can turn down? I'm not familiar with the number however it would make sense that there would be one.
I'm uncomfortable (ache) at about 20mm (40°). About half that looking up.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
The Definity is possibly the most asinine marketing bit ever. Lets put "Ground View" (love that name.) in the lens below the reading segment.
umm, hold on, lets add this up if there is a 18mm seg height going into a 28mm B measurement frame , that means that the distance is 10mm intermediate is ~9mm (4mm Drop) and reading area is ~5mm. That fabulous 'GroundView" was left on the edger. To make it work you'd have to have a seg height of at least ~24mm! That's only if the full add actually shows up with a min seg height of 18 which I would strongly doubt.
I agree with Robert, Listen less to the Marketing, follow the design.
- Optician
- Frame Maker/Designer
- Teacher of the art of crafting handmade eyewear.
The Definity has a short corridor version that can be fit at 15. I try not to fit minimum heights. I have one being picked up today in a short that's fit at 24.
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