Surfacing or Uncut blanks?

[ilanh]

This is probably an incredibly basic question but I would appreciate an explanation if possible. Is there a big advantage in asking a lab to surface a pair of lenses to order, as opposed to edging uncut blanks? It seems that uncut blanks can be obtained (and edged) at a price that is significantly less than surfacing. Therefore, I would assume that surfacing produces better quality? Is this for all prescriptions and lens materials or does it vary? Can anyone reccomend various parameters when one would use uncuts vs. surfacing?

I just had 2 pairs of glasses made for myself (-1.25 OU). One pair was poly fully surfaced by the lab and one was uncut blanks. The price differential was large but I could not tell a difference.

Ilan

[shanbaum]

It is near-universal practice to use finished lenses when it's possible to do so, surfaced lenses when it's not. "Possible" means, the desired thickness and layout properties can be obtained in the finished spectacles.

Surfacing affords greater flexibility in achieving both of these, at least with certain types of lenses; for example, additional decentration can be obtained using a semi-finished blank of a given diameter over that which can be obtained with a finished blank, by grinding prism to induce decentration in the surfaced blank (at least in the case of non-aspheric single vision lenses).

The more important advantage, however, comes in the case of plus-powered lenses, which can be surfaced to a thickness appropriate to the particulars of the order, including the frame shape, Rx, and layout parameters. The thickness of finished stock lenses, on the other hand, is determined by their diameter, and there are but a few diameters available.

So, the short answer to your question might be that there may well be no advantage to surfacing minus Rx's, but there will frequently be an advantage to surfacing plus Rx's.