Can anyone tell me if there is truly a difference between the Gradal Top and the new GT2 ? I know what the lens sales people say, but they are just trying to sell their product. Thanks...
Can anyone tell me if there is truly a difference between the Gradal Top and the new GT2 ? I know what the lens sales people say, but they are just trying to sell their product. Thanks...
I just caught this thread, but I'll post a few comments.
GT2 by ZEISS is similar to Gradal Top, and offers many of the same basic features or design traits, including a very expansive distance zone, a relatively wide progressive corridor, and a soft periphery. Contour plots of these two lenses will demonstrate that Gradal Top and GT2 have virtually no surface astigmatism above the 180 line, and the gradients of power and astigmatism are very low. Both lenses have also been optimized for the position of wear, and make use of an aspheric Base curve series, variable near zone insets, etcetera.
However, GT2 has a significantly shorter corridor length than Gradal Top. The new corridor length is roughly 2 mm shorter than Gradal Top's, and was based on extensive head-tracking data. The near zone is now higher up, and wider at the same vertical drop, which improves overall near utility. GT2 has a minimum fitting height of 17 mm, compared to Gradal Top's 18 mm. With its shorter corridor length and higher, wider near zone, GT2 has up to 50% more near utility in smaller frame styles compared to several other leading progressives.
Additionally, there have been a few other refinements to make GT2 easier to process and dispense. For instance, the Base curve series has been streamlined some for easier surfacing and inventory management. Also, while GT2 has still been optimized for the position of wear, Zeiss has constrained the optimization at the distance and near measurement points in order to preclude the need for "measurement values" or a compensated prescription. Finally, the position of wear values used during the optimization process are now based upon average US measurements (Gradal Top's values were based on averages in Germany).
Darryl J. Meister, ABOM
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