Lenses Thickness - Stock v. Grind

[Lulu]

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

[lensmanmd]

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.

[PRECISIONLAB]

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

[MIOPE]

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.

[Oscar]

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.

which spin coat machine do you have? i've only seen the statisloh one and the heat is applied during the UV curing process. Can't avoid the warpage unless you dip it or increase the ct

[MIOPE]

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.

[LENNY]

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...

[lensmanmd]

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...

Frame size and proper fit trumps the minuscule 0.5mm difference. Lenny is correct calling you out!

[Oscar]

Frame size and proper fit trumps the minuscule 0.5mm difference. Lenny is correct calling you out!

please tell that to the many opticians crying about 0.3mm tolerance. wah wah i want 1.4mm but these are 1.7mm now my et is through the roof. meanwhile it's a high-wrap, high-minus with 8mm horizontal decentration per eye and an OC of 30mm.

[lensmanmd]

please tell that to the many opticians crying about 0.3mm tolerance. wah wah i want 1.4mm but these are 1.7mm now my et is through the roof. meanwhile it's a high-wrap, high-minus with 8mm horizontal decentration per eye and an OC of 30mm.

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.