bunyip wrote:

Jacko wrote:I wear prescription multifocal glasses. I get supersavers 2 for 1 deal when I get a new prescription.
1st pair are prescription polarised sunglasses that I wear on the yak or when driving in glarey conditions.
2nd pair are prescription photo chromatic that are normal indoors (or behind windows in a car) and darken to reduce glare in outdoors bright sunlight.
Unfortunately you can't get polarised and photo chromatic on the same lens.

mine are photochromatic which is why Ihave the magnetic additional front lens, they look no different when attached.
I don't know who told you that photochromatic and polarised are not available in the same lens as I HAVE HAD them for many pairs of glasses in the past.

Sorry - should have said photochromatic and polarised are not available in the same lens with the 2 for 1 deal from specsavers. edited

I lost my multifocal polarized photochromatic spotters a few years ago. they were good, but didn't go clear inside just lighter. I was advised that polarized glasses were not the best for driving because of the effect it created when looking through laminated glass (or something to that affect). I do wear my polarized sunnies in the car on a bright day though (two for one specials from spok savers). Trying to avoid the cataract thing for as long as possible.

Laminated glass is fine, it is the zone toughened glass that presents blotches and I haven't seen those in windsscreens for about 40 years, however, they can present problems with reading the older style lcd instrunents in cars, the new ones are ok but not all car makers use them, you will see them on pumps at the servo and will black out, older mobile phones were the same.
Photochromatic also comes in varying spans of darkening and also speed of darkening and recovery, glasses makers try to match pupil dilation speed to the optics.
Welding helmets on the other hand are very fast and power assisted.

I saw the optometrist today and got my eyes tested, found i need new glasses, i also bought Jonathan paul fit overs and will see how i go with these for a few weeks then reassess, my situation.

I used to use the magnetic clip on type but found that if I got a face full of spray it tended to stick around between the layers of glass, plus twice the surface area to clean.

May be of interest to you from the years I spent with the owner of Spotters on various fishing trips and expos.
The lens on these and most glasses are made from two layers of material (glass, CR39, Polycarbonate or Acetate which scratches very easily) and the polarising and photochromatic feature is a membrane that is sandwiched between the two, this applies to almost every brand on the market, the lenses are generally made overseas and come in as a large disc that is about 9-10 cm in diameter, the lenses are either plain or ground to a prescription and are ordered to suit the optical requirements, when they arrive they go into a grinding machine, there is a template for each frame type and the lens is aligned in the machine and ground to shape then fitted in the frame.
If the alignment is slightly out and the lens is polarised it will present problems in many ways such as double vision especially on water when there will appear to be two surfaces.
Polarised lenses are used at 3D cinemas and are aligned left to right and right to left, ordinary lenses are aligned up and down and both the same.
The military do not use polarised as many displays are LCD and they will either fade or black out, I imagine commercial airlines would be the same.
Photochromatic lenses come in a lot of colours and variables from almost clear to very dark or a narrow span in the darkening spectrum, the time for darkening is generally faster than lightening, most opticians won't tell you this as it will simply be too confusing so they just go with what is deemed to be the most acceptable.
Photocromatics often will not work when driving a car as they need direct sunlight to work, I have clip ons for this reason when driving but my glasses while photochromatic are not polarised, the clip ons are and partially negate the effect of the photochromatic action so in direct sunlight they are not too dark.
Photochromatics also go under the name transitionals.