Do every freeform lens have backside progression.
some one in the proffession told me this, do any of you, know if this i realy true ?
best regards
Peter
Do every freeform lens have backside progression.
some one in the proffession told me this, do any of you, know if this i realy true ?
best regards
Peter
Many Views no one dear to reply ?
It's a difficult question, because the term "freeform" (and "digital") are used to mean different things; there is no consensus. Dr. Cook has suggested the following: "Digital" = produced on digital equipment; "Free Form" = A digital lens that has at least one major meridian corrected exactly for its power for at least one aberration; "Individualized" = A digital lens tailored to prescription, patient, and frame (i.e., position of wear).
"Digital" equipment (in this scheme) refers to generators that cut surfaces with such high form accuracy and such low surface roughness that surfaces may polished on polishers using conformable laps - laps that conform to the shapes of the generated lenses, instead of making the lenses conform to the shapes of a scalar set of laps.
There are lens designs on the market that comprise progressive surfaces on the front with aspheric, or atoric, surfaces on the back. There are designs that have progressive surfaces on the front and back. Then there are some of the Hoya lenses, that have front surfaces that defy explanation (at least for me - I'll let my friend RT explain them). I don't think we have agreed-upon terms that would distinguish such lenses from all-backside progressives (i.e., lenses having spherical front curves).
There are some designs that are "freeform" surfaced on both front and back.
There are also lenses that require digital surfacing equipment to create, but are not progressives. These include "freeform SV" products like Auto II SV and ID SV, bifocal products like TRO Round Seg, ST28 IQ, etc. Also don't forget freeform produced backside slab-offs. None of these will have a "backside progression" but do have backsides that are more complex than mere toric curves.
So I would say "No", every freeform lens does NOT have a backside progression.
RT
As the others have indicated, the short answer is "no." But to elaborate on some of the insightful comments made by Robert and Rick, there are obviously various arguments over the semantics:Do every freeform lens have backside progression
- Some companies reserve the term "free-form" to describe progressive lenses that have had some or all of the progressive optics component fabricated using free-form surfacing. Examples of such lenses include ZEISS Individual, Hoyalux iD, and Shamir Autograph II.
- Other companies may apply the term "free-form" to any lens that has had at least one complex surface that lacks point or axial symmetry applied to the lens using free-form surfacing. Examples of such a lens would include Varilux Physio 360 Enhanced Fit.
The original Hoyalux iD is an example of a lens with partial progressive optics on both the front and back of the lens. Further, while most ZEISS Individual lenses employ back-side progressive lens designs in the US, Individual lenses in Europe may have the progressive optics fabricated using free-form surfacing on either the front or back of the lens blank in order to extend the prescription range.
Of course, for the patient, eyecare professionals should focus on the possible patient benefits provided by the lens, not the manufacturing technique. And then there are some potentially misleading uses of the term "free-form," often for marketing purposes:
- Some companies may apply the term "free-form" to semi-finished lenses that have been fabricated using traditional molding techniques, if the molds were made using free-form surfacing. Several manufacturers use free-form surfacing or CNC milling to make progressive molds now.
- Some companies may use the term "free-form" refer to any lens that has been surfacing with a free -form generator, whether or not the surface involved is actually complex in shape.
Best regards,
Darryl
Darryl J. Meister, ABOM
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