Here's a silly "DERP" question

[oxmoon]

With that amount of cyl. I personally would not use POW and the resulting compensated formula.

Please tell me why.

[DanLiv]

I remember someone (DM?) saying that the main idea with high plus aspherics is 1. flatten the lens, 2. thin the lens, 3. try to make the correct aspheric corrections so the vision doesn't go all to hell.

Is this the issue? Some aspherics are more "aggressive" than others? And FFSVs are just "another" type of aspheric (i.e. GIGO)?

With finished lenses and and traditionally surface aspherics I think the primary concern is the flattening/thinning. I believe the abberation correction is exploited to allow the lens to deliver acceptable optics much further off the proper corrected curve (e.g. a +4.00 might get good optics on a spherical 10 base, better on an aspheric 10 base, but usually the aspheric will be done on a much flatter 6 or 4 hoping the aspheric correction will compensate for the errant base curve, resulting in only the same or slightly worse vision than the spherical 10 base but extremely reduced thickness). FFSV typically concentrates more on exploiting the atoric design for maximum vision on the correct curve lens. Therefore the FFSV would be best vision, but probably no thinner than a spherical lens. The traditional aspheric would be much thinner, but without any vision gain over spherical. Free form designs can of course be changed to accommodate either vision or thinness, but I think the default is correct curve. Ig you want it thinner, order your FFSV on a curve of your choice and the software should still compensate as much as it can.

[Paul Smith LDO]

Please tell me why.

Post 10 and 15 in this thread sum up past experiences.

[Barry Santini]

When we say "proper curve" we are talking about proper "spherical" base curve.

There's so much more that can be done today with FF, aspherics and both.

B

[drk]

With finished lenses and and traditionally surface aspherics I think the primary concern is the flattening/thinning. I believe the abberation correction is exploited to allow the lens to deliver acceptable optics much further off the proper corrected curve (e.g. a +4.00 might get good optics on a spherical 10 base, better on an aspheric 10 base, but usually the aspheric will be done on a much flatter 6 or 4 hoping the aspheric correction will compensate for the errant base curve, resulting in only the same or slightly worse vision than the spherical 10 base but extremely reduced thickness). FFSV typically concentrates more on exploiting the atoric design for maximum vision on the correct curve lens. Therefore the FFSV would be best vision, but probably no thinner than a spherical lens. The traditional aspheric would be much thinner, but without any vision gain over spherical. Free form designs can of course be changed to accommodate either vision or thinness, but I think the default is correct curve. Ig you want it thinner, order your FFSV on a curve of your choice and the software should still compensate as much as it can.

Killer explanation. Thank you.

[Barry Santini]

Killer explanation. Thank you.

In higher plus, disagree.

B