Base Curves For Plastic Frames>>

**sandeepgoodbole** · 10-01-2002, 07:37 AM

If the Cyl is generated on front surfaces, plastic / Carbon frames buckle and pop the Lens out at the eyebrow side.
(Buckling also depend on the shape of frame and the axis of the lens) More the cyl, more the buckling. Apart from using Minus side Cyls, are there any alternatives which will make the frame "behave" decently with such lenses ? I am refering to Out side Base +6 @ 1, or more cyl powers in Glass 1.523.
Like : Plano @ - 3 Cyl
=
+6/+9 On Front
-9 on the Back.
These are the combinations used by Indian Mass Producesr of the Lenses. I do n't know why they prefer it. Most probably, outside Cyls take lesser time and fewer sands and saves them a lot.

**John R** · 10-01-2002, 12:39 PM

Ideal lens curves for some wrap round frames, but not to good for anything else.
I think what the manufacture has done is bought some of the old moulds that some optical co must have had kicking around.
I can tell you with modern macheniery running curves on the front of the lenses is a real pain in the neck as they are not designed for the job...

**Rich R** · 10-01-2002, 12:48 PM

Most edgers follow the bevel from the front curve of the lens, the newer edgers can put a 5 or 6 diopter bevel on an 8 base lens making it a better fit.
One option may be to edge the lens a little bigger and change the bevel to better fit the frame.
Rich R

**Texas Ranger** · 10-01-2002, 04:31 PM

sandeep, now I remember one of the bettwer reasons why we opticians in the USA rejoiced when the industry swithed to minus cylinder form lenses, about 30 years ago; in the example you used, could you not get a "base curve" flatter than a 9D, like a
- 6.00 back, +3.00, +6.00 front; better would be a +4.50 front, with a -4.50, and -7.50 back, nice job, no problem in frame mounting. are lenses all done in plus front side cylinders there? or is an option?

**sandeepgoodbole** · 10-03-2002, 01:13 AM

Texas Ranger said:
are lenses all done in plus front side cylinders there? or is an option?

The mass producers of Single Vision lenses are different than those who finish Kryptoks.
Kryptoks are just enough to demotivate them ,as the Reading Segment gets eliptical or Non Circular shapes. So, they have no options.
For the single vision mfrs, they probabaly think that it's as universal like Newton's Law and cyls cannot be made from inside!
Awareness, communication and desire to improve are the only steps to change this.

:cheers:

**John R** · 10-03-2002, 01:25 AM

sandeepgoodbole said:
they probabaly think that it's as universal like Newton's Law and cyls cannot be made from inside!
Awareness, communication and desire to improve are the only steps to change this.

Just remind them that the rest of the world uses minus cyls 99% of the time...
I fear the problem is more likly that your country has got all the old machinery that is no longer used over here, so untill they upgrade to the newer machinery (big money outlay) you will not see a end to the problem other than sourcing from another country.

On another point which sort of ties in with what i'm saying a lot of UK companies are now moving their call center's over to India as its cheaper to employ staff than in the UK. A wage quoted was £10.50 a week in India againist £151 in the UK....