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I am new in freeform. IOT just installed
Has a request of a job bifocal +10.00 add 2.50 blended on Poly
At this moment i just have on stock single vision blank base 9.75 on poly. But the inside curve is arround -6.00.
The center thickness of the blank is not enough.
Also, the diameter of the blank is not enough. The digital blended is not being rotated by innovations or IOT.
So advise is welcome.
Also, where to buy thick high base single vision poly blanks.
You're going to need a 12 base for that lens and I've heard a lot of labs have not perfected the calibration on backside round segs.
I would try x-cel for the thicker blank and base.
X-Cel's spherical 1.55 comes in +10 bc extra thick and +10 and +12 standard thickness, specific values unknown.
You'll need a steeper than normal (compared to front aspheric) base curve so the software has some curve, probably at least -2.00, to work in the needed asphericity. Poly, 1.67, and 1.74 is very dispersive at this power, especially with a multifocal. Avoid if possible.
Ideally you want a front aspheric, but I don't believe most of the FF softwares can work with them, although Quest is making Essilor's Super Modular on a FF platform, but I wonder if then optimizations are limited to an atoric back surface.
Note that Signet Armorlite has a 1.56 aspheric FT28 with a +9.75 (true curve unknown) that might work.
Hoya may have steeper Trivex base curves. No details.
CR39 should be on the table. In an optimal frame/lens/eye configuration it can be reasonably light in weight and not thick at the edges.
http://www.bcdlens.com/products/aspheric28.aspx
While not recommended for Optics, you may be able to make a biconvex blended. Its not ideal but someone with that power is also used to narrow visual fields. I would consider this option only as a last resort.