What is semi-finished lenses?
Factory has already injection cast one side of the blank lens, leaving other side blank without grinding to operate the prescription. This is a raw material of freeform lens.
Unlike finished lenses, semi-finished lenses do not have a fixed prescription; you can process them to produce the prescription you want.
What is the base curve?
The front side of semi-finished lens is confirmed and can’t be changed, base curve is the curvature of this front surface.
In Trust industrial the base of Semi-finished lenses include 0, 2, 4, 6, and 8. Different base curvatures are suitable for different frames and correspond different power.
It’s important to note that 0, 2, 4, 6, and 8 are nominal curvatures, not actual curvatures. Processing usually need referring to the actual base curve of manufacturer’s specifications.
How is the base curve influence lens:
- With the bigger of base curve, lenses front side is more curved; the lens maximum prescription is confirmed if base curve is in certain;
- For sport or bicycle frames, it requires lens base curve from 6.00 or 8.00 base, smaller base curve can’t suit with demand.
- if the base curve is wrongly, thought lens prescription is correct, patient will feel dizzy when wear the lens
How to reduce or avoid the negative affection from the base curve?
- To be ensure the accuracy base curve lenses you’re ordering from factories, all semi-finished lenses from Trust industrial have its specification sheets.
- There have 2 types of operation way usually: Freeform surface CNC turning (fully automated digital lathe), like IOT or Optotech. Another way is traditional aluminum carports, regular grinding (suction cup aluminum discs, traditional fixed curvature grinding molds), traditional production method.
- When the prescription is very high (Above to -8.00), the disadvantages oftraditional freeform will be significantly different from those of fully automated garages.(Because 100% automatic can calculate and compensate for peripheral prism, distortion, and oblique projection aberrations caused by base-bend mismatch point by point; while traditional freeform machines cannot.)
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