Lenses for glasses wearers

[Eric F]

Hi all,

I've recently annoyingly discovered that my glasses produce a slightly clearer image if I look through the very bottom of the lenses. To do this, however, I need to tilt my head back slightly and look downwards slightly - if I keep at this I'll either fall & have an accident or put my neck out!

With all the debate about lense quality in binoculars, has there ever been any investigation into the quality of lenses available for glasses and for that matter the coatings too.

Many glasses these days come with some form of anti-glare coating and I think you can get hold of "flattened" lenses, which might be the problem with my glasses.

Any thoughts on this subject - or can you point in the direction of an old thread if need be?

[elkcub]

Hi Eric,

May we assume your glasses are not bi- or tri- focal? IMO the use of eyeglasses throws a random element into the mix. Not only are the factors you mentioned at work, but also magnification differences, off-axis effects, etc. In another thread I've asked why binoculars aren't made so that personal prescription lenses can be inserted at the ocular — but basically that's put off as whacko.

Elkcub

[Robert Ellis]

When I got my latest pair of spectacles I had the choice of basic lenses or upgrades from Nikon or Zeiss. Glass of the highes quality can be had in specs these days becuase the big names in optics are very strong in the medical imaging and lens fields.

[Pileatus]

When I got my latest pair of spectacles I had the choice of basic lenses or upgrades from Nikon or Zeiss. Glass of the highes quality can be had in specs these days becuase the big names in optics are very strong in the medical imaging and lens fields.


Robert,

Crown glass is no longer popular for eyeglasses. Most give you a choice between plastic or polycarbonates and each choice dictates lens thickness, level of aberration, and ultimate cost. Plastic (CR-39) is the most common and inexpensive; polycarbonates can be lighter, thinner, and cost 2-3 times as much as CR-39.

Guess what? CR-39, the most inexpensive choice has a lower index and a correspondingly higher Abbe value, which means they will produce less chromatic aberration than polycarbonates.

Read about Abbe values (near the end of the article)
http://www.2020mag.com/ce_article.asp?page=ce/2889/lesson.htm
and you'll see that inexpensive CR-39 with AR coating is perhaps the best combination for most users.

John

[Robert Ellis]

Ahhh, John, you are right. I call it glass but I always forget that it is poly. Both the Nikon and Zeiss offerings were high end poly with their fabulous anti reflective coatings. I chose the Nikons for the thinness, but am finding a tiny bit of CA caused by my glasses, but only from bright lights (headlamps) aftar dark.

[Pileatus]

Hi all,

I've recently annoyingly discovered that my glasses produce a slightly clearer image if I look through the very bottom of the lenses. To do this, however, I need to tilt my head back slightly and look downwards slightly - if I keep at this I'll either fall & have an accident or put my neck out!

With all the debate about lense quality in binoculars, has there ever been any investigation into the quality of lenses available for glasses and for that matter the coatings too.

Many glasses these days come with some form of anti-glare coating and I think you can get hold of "flattened" lenses, which might be the problem with my glasses.

Any thoughts on this subject - or can you point in the direction of an old thread if need be?

I'll offer some simple advice that may help.

Assuming your prescription is correct, two things MUST be done to obtain the best view through a pair of eyeglasses.

First, the optical centers on the lenses need to be vertically aligned with YOUR pupils. Look at your frames in a mirror and if your pupils are not vertically centered in each lens, you may have a problem. Many times they just put the optical centers in the vertical center of the lens and this may or may not be aligned with YOUR pupils. It happened to me.

Second, the IPD must be set correctly for YOUR eyes. Furthermore, the distance from the eyeglass bridge to your left pupil may be different than the distance to your right. If they measure your IPD and simply divide by 2 you may have problems. Let's say your IPD (distance between pupils) is 60mm. Well, one side, could be 29mm from the nose bridge and the other 31mm. If they set it at 30mm on each side, neither pupil will be perfectly aligned. This also happened to me!

Learn your measurements and insist that your optician adjusts for the variations in eyeglass frames and your individual IPD measurements. Believe me, it makes a difference.

John

[Eric F]

I'll offer some simple advice that may help.

Assuming your prescription is correct, two things MUST be done to obtain the best view through a pair of eyeglasses.

Learn your measurements and insist that your optician adjusts for the variations in eyeglass frames and your individual IPD measurements. Believe me, it makes a difference.

John

Thank you all for your responses.

John, your words sound like sound advice - I think I should be more careful when buying my next lenses.

I do have standard plastic lenses (not bi or tri-focal) and I'm sure they're spot on with the prescription too, as when I look through my glasses in a way that produces a clearer image, I can read more detail than a friend at long distance.

Comments re the drawbacks of polycarnonate lenses has made me think twice about these - I'd thought the thinner (possibly flatter) poly lenses would give less distortion. Maybe with a Nikon or Zeiss coating they'd have an edge?

Guess I've just got to find a good, reliable Glasses company now when getting my next pair and make my requirements clear. Thanks again.

[Pileatus]

Thank you all for your responses.

John, your words sound like sound advice - I think I should be more careful when buying my next lenses.

I do have standard plastic lenses (not bi or tri-focal) and I'm sure they're spot on with the prescription too, as when I look through my glasses in a way that produces a clearer image, I can read more detail than a friend at long distance.

Comments re the drawbacks of polycarnonate lenses has made me think twice about these - I'd thought the thinner (possibly flatter) poly lenses would give less distortion. Maybe with a Nikon or Zeiss coating they'd have an edge?

Guess I've just got to find a good, reliable Glasses company now when getting my next pair and make my requirements clear. Thanks again.

I wear the lightest polycarbonate lenses with AR coatings and they are just fine. Astigmatism is my real enemy and I must wear eyeglasses when using my bins. A simple diopter adjustment doesn't satisfy.

I suggest you take your eyeglasses to an optician who can mark the locations of the optical centers with a felt tip pen. THAT will show you if everything is lined up with your pupils. If not, I'd strongly suggest having the lenses recut...free of charge! I went through this whole process quite by accident, but that's another story for another day.

Good luck,

John

[mcdowella]

If you have an accident, plastic may reduce the chance of you getting hurt from broken lenses.

In the UK I think Dollond & Aitchison offer Nikon lenses. My current ones are Pentax, from Boots (my prescription is odd and if Boots do own-brand lenses they don't do ones for me). I may try Nikon next time round, partly because I have been unlucky recently at my local Boots. By the way, if you want to get your glasses correctly aligned, get them to use a qualified dispensing optician to measure you up for your frames (otherwise you may get a qualified optometrist writing down the prescription, with the frames fitted by somebody working from experience rather than a full course of training). Some of my problems with Boots come from the mismatch between me wanting to get measured up for glasses on the weekend and them having the nearest real dispensing optician in the next town, coming out to the sticks once a week for extreme cases like me.

[etc]

First, the optical centers on the lenses need to be vertically aligned with YOUR pupils.

It's harder to do wearing glasses, easier without glasses.

[Pileatus]

First, the optical centers on the lenses need to be vertically aligned with YOUR pupils.

It's harder to do wearing glasses, easier without glasses.
I was referring to the optical centers on the lenses of eyeglasses, not binoculars.

[etc]

I had a bad experience with an anti-glare coating, it came off after a few months of usage. Very fragile, even when cleaning with a microfiber cloth.

If you get an AR coating, get the most expensive one like Crizal, which is baked on, not dipped.

I've used either polycarbs or CR39 lenses all my life. I think my next pair of eyeglasses will be real glass, with a baked-on AR coating. I do realize they will be heavier, but having the highest Abbe value, and thus sharpness.