Hi,
Anyone have an explanation to why a -7.00DS 1.74 STOCK would be thinner than the same in 1.74 GRIND?
Currently using Essilor.
TIA
Hi,
Anyone have an explanation to why a -7.00DS 1.74 STOCK would be thinner than the same in 1.74 GRIND?
Currently using Essilor.
TIA
FSV is molded, not ground. This reduces heat induced aberrations, allowing for thinner lenses. You will find this with TVX, 167, Poly, 1.6, etc.
Although 1.74 is available as semi finished, lens that are ground in house are set to 1.5 and above center thickness due to issues that arise from traditional in lab back side spin coating machines. The suction and UV cure will almost always warp thin (1.0) 1.74 lenses. The preferred back coat for 1.74 is the drip coat process which only a few labs have as part of surfacing.
Finished is always the preferred
Last edited by PRECISIONLAB; 03-29-2019 at 07:29 AM.
There is a workaround for the suction problem. Put blue tape on the front curve of the 1.74 lens.
Then use a second lens ( poly, cr39, etc) that has the concave curve matching the base curve of the 1.74.
Use a strong two side adhesive tape to join the two lenses. The suction would be on the other lens and not
on the 1.74.
For the heat problem, we use the oven that was used witb the mini old machine. Looks like the heat
Is not so strong on it. Maybe because the oven is not permanently on.
But we do not grind 1.74 thinner than 1.5mm anyway.
That oven come with the Ultraoptics MiniII. The oven and the coater are two separate machines.
Regularly we use the Ultraopticas MRIII but not for 1.74. It is too hot.
People! Its only 0.5mm difference!
Stock, depending on manufacturer and the size of the edged lens could be thinner because of the higher asphericity...
Not just Canada. We get that here in the States, too.
Like two sheets of paper is visible to the naked eye. SMH. This is optical, not rocket science. Many opticians can’t wrap their heads around the concept of proper fit, and rely on IoR.
I have LDOs asking for recommendations on frame size, with high PRPs. Absolutely no concept of how decentration affects finished thickness.
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