Question 2

[Suzzane]

The segment height of a traditional bifocal is measured from the top of the segment to where?

a. The eyewire directly below the optical centre. b. The deepest point of the eyewire. c. The top of the eyewire.

[Lensman11]

Deepest point in the eye wire

[Loki]

Deepest point of the eye wire, also known as lowest tangent. It can also be measured to below HCL (horizontal centre line) but the obviously isn't one of the options.

[Uncle Fester]

Welcome to Optiboard Suzzane!!!

The "groove" of the frame that a "beveled" lens fits into is also known as the bezel. If you did not know that already put them in your optical vocabulary.

Another way of saying that's what you are measuring too.

It varies.

Anyone know what frame makers use as a rule to create these depths?

[uncut]

I believe the answer, Uncle Fester, is the BOXED measurement method. This method replaced the datum system.

[Uncle Fester]

I believe the answer, Uncle Fester, is the BOXED measurement method. This method replaced the datum system.

Actually my poorly worded question is, is there a "standard" depth to a bezel in a plastic/acrylic frame? Is it based on a relationship between the size of the eyewire in a metal frame? I suspect that the designer would use their experience to determine them but am curious if there is some type of industry ratio.

[rbaker]

The "boxing method" is the gold standard. Long retired, I still have my Box-O-Graph in my archives.

[uncut]

Uncle:


I believe that there was a standard called the "frame difference" when there were few lens shapes being produced.

With the introduction of fused glass bifocals in standard blank size and set insets, the influence was generated by restrictions of minimum and maximum bifocal heights.

Today frame makers have hovered between a standard minimum B, a set B dimension in all available eye sizes, and 2 or more millimeter steps increases matching differences lock step with A increases.

[Lensman11]

Uncut
if you keep the b constant and increase the a you will have a different shape with each size never saw a frame with those characteristics.

[Barry Santini]

Uncut
if you keep the b constant and increase the a you will have a different shape with each size never saw a frame with those characteristics.

Then you haven’t look very hard. Safilo frames did it all the time!

B

[Uncle Fester]

My question is not about the a, b, ed- but how deep just the groove of a frame is. Who determines that and is there some type of rule of thumb because I see them vary.

[drk]

Can't be more than a millimeter.

[Uncle Fester]

Can't be more than a millimeter.

The Zyloware Invincible sure seemed like more the a millimeter. Especially when you were burning your thumbs and fingers off trying to remove a PGX lens that was edged sightly large!!!

[drk]

That's why it was invincible, I guess.

[uncut]

Uncut
if you keep the b constant and increase the a you will have a different shape with each size never saw a frame with those characteristics.

You are right to assume this if a frame is produced in a maximum of one or two sizes....

Essilux, back in the days of early Luxo, when all frames were vertically challenged rectangles, made a few of their models in three to four sizes(A) with the exact same B dimension.

I believe it was done so to avoid angering the rectangle gods?