PAL fitting heights vs width of corridor

**mullo** · 08-04-2005, 09:31 AM

I have a PAL related question reagrding minimum fitting heights and amount of reading area. If a given PAL design has a recommended fitting height at (for example) 18mm; if you fit at 18mm as compared to 20mm, are you sacrificing any reading a) width and/or b) depth.

My understanding is that fitting at the recommended height will lend 100% of reading power and should be at the widest width of reading. I have debated with others, they feel that the further you increase to 20mm or 22mm that the width/reading area should also increase. I also understand that you will obtain more depth/area to read with such a seg ht increase but not really any width. Can I get your opinions on this.....Thanks, Mullo

**Darryl Meister** · 08-04-2005, 03:15 PM

My understanding is that fitting at the recommended height will lend 100% of reading power and should be at the widest width of reading. I have debated with others, they feel that the further you increase to 20mm or 22mm that the width/reading area should also increase.

For many designs, the near zone does indeed continue widening below the near reference point.

**mullo** · 08-04-2005, 07:12 PM

For many designs, the near zone does indeed continue widening below the near reference point.

So this is for "many" designs" but shouldn't be a generic assumption that it occurs in all PAL's. I guess it is safer to say that it is in some designs but not in others. Then by fitting "many" progressives at the minimum recommended fitting height, we are not offering the best/widest field of near vision possible.

As always, thanks for your reply Darryl!!

**Darryl Meister** · 08-04-2005, 07:30 PM

The near zone width of most designs continues to widen below the near reference point, but it varies from design to design. Some actually continue to flare out by a considerable amount below the near reference point (like SOLA's VIP). Some don't change much at all below the near reference point (like SOLA's SOLAOne). Still others eventually start to narrow slightly at a far enough distance below the near reference point. It really just depends upon how the lens designer controls the shape of the near zone and distribution of the progressive optics around it.