Opthalmic lens quality question

[eyeguy21]

Would any of you on the lab or lens manufacturing side care to expound on the issue of lens quality? I've seen quite a bit come up on recent threads in regards to 2nd's and 3rd's or A,B,C quality levels. My lab experience comes from a 1-hr lab a while ago so it's pretty limited. I'm curious as to what factors determine whether it's a grade A lens or B, etc. and at what point That's decided. In other words is it determined during the manufacturing process or at some other point?

I've done some brief surfing for it but most of the information that comes up seems to be about camera/telescope lenses. Any web information on this issue is welcomed too.

[MikeAurelius]

In regards to which aspect of lens quality? There are many, so let's agree on one or several to discuss.

[eyeguy21]

I have a basic idea of what a 2nd or 3rd is but what is the difference between A and B grade lenses and at which point of the manufacturing is this determined.

[DragonLensmanWV]

I think it would boil down to how far they are out of strict tolerance. As Mike noted and I said, we used to get FT-25 lenses that the segs were offsize by 2 mm. That would not qualify them as First Quality.
And years ago (30 or so) I knew a guy from Chicago that could get me very cheap lenses from Venezuela. Problem is they were CR-39 and had fingerprints embedded in them. But hey- they were very cheap!

[MikeAurelius]

I think the A,B,C indicators are equivalent to 1st, 2nd and 3rd.

[eyeguy21]

I think the A,B,C indicators are equivalent to 1st, 2nd and 3rd.

Ok, so this is basically why I asked this. Some refer to it one way and some the other and it can get confusing but the answer DragonLensman gave was helpful where he mentioned CR39 that had fingerprints in the lenses. That's the sort of thing that I was after. From the opticianry side of the business we don't often hear about those sorts of things. I put it to my local source as well as my manager, who then passed it on to our Lab manager and the question confused them all.

I get mixed opinions on how important this question is. Some think it's important while others feel that with today's technology and standards most of the issues that revolve around substandard materials are weeded out before the lenses hit the shelves. Is this your experience or do you see it often. Maybe I should have said what types of defects/manufacturing issues have you seen that would qualify as sub-par quality.

[MikeAurelius]

It is going to be more of an issue in the lab than it is in the store.

Labs try to find the least expensive way to make a lens, and sometimes, a lower quality lens will suffice. When you are making a lens for a 48 mm frame, you can certainly use a 71 mm blank that has severe edge chips (which would qualify as a 2nd from most manufacturers). You, in the store, would never know the difference.

That's why I wanted you to qualify your statement somewhat, so we can talk apples and apples.

[eyeguy21]

It is going to be more of an issue in the lab than it is in the store.

Labs try to find the least expensive way to make a lens, and sometimes, a lower quality lens will suffice. When you are making a lens for a 48 mm frame, you can certainly use a 71 mm blank that has severe edge chips (which would qualify as a 2nd from most manufacturers). You, in the store, would never know the difference.

That's why I wanted you to qualify your statement somewhat, so we can talk apples and apples.

Absolutely. It makes more sense now too. Now that you mentioned the severe edge chips I'm having all sorts of flashbacks of lens blanks that had bubbles on the edges and such. Something like that would probably qualify as a 2nd.

[IC-UC]

Could you be referring to the different zones in a lens that manufacturers consider before judging a lens to be wasted?

[eyeguy21]

Could you be referring to the different zones in a lens that manufacturers consider before judging a lens to be wasted?

Possibly? I'm not completely sure of all of the different elements that might factor into the quality of the lens blank. Like Mike said, us opticians don't really see that side of the business. I'd welcome your take on the 'zones' because once again it's something unfamiliar to me.

[eyeguy21]

fingerprint is really a problem. but why CR39 is a problem too?

I think he may have been referring more to where the lenses came from than the material. Not to mention that he's talking about 30 or so years ago when CR39 usage was probably in it's heyday. Are you saying that you see a lot of fingerprints on lens blanks now?

[Barry Santini]

I don't think you can now separate the lens quality issue from the fit any longer

As Robert M points out, POW/fit adjustments, material choice, abbe, BC all CONTRIBUTE TO A CLIENT'S IMPRESSION OF LENS QUALITY.

Heck, you take an RX, say -1.00 -3.00, AND FIT STK fINISHED LENSES with Avance in 1.6, but without regards to Martin's rules, etc., and then

Fit the same POLY in Auto II SV or Zeiss Indiv SV, with proper pupil measurements and the rest, and come back and tell me what lens appears superior quality to the client?!

B

[eyeguy21]

I would agree with that Barry. With this thread I was trying to get some input from some of the lab oriented types to sort of bridge the gap in my knowledge between working in a 1-hr lab in the 90's and working strictly as an optician for the last 15 or so years. I never have had the experience of ordering lenses since it was all done at the corporate level.

I've been around long enough to hear quality horror stories from some of my contacts about blanks that had been ordered on the cheap but given that the end product (generally) falls within ANSI standards I just assumed that this wasn't an issue for most.

[IC-UC]

In regards to the zones, what usually happens is that the lens is seperated into 3 zones.
Zone 1 is the area in the centre of the lens and is 35mm in diameter.
Zone 2 is the ara outside of this, up to 5mm from the edge and Zone 3 is the outer 5mm edge.
In each of these zones you would have permissable defects that would be allowed. Defects are rated on the size and brightness of the spot and also length and width of scratches.
It all gets a bit complicated, but once you know what is allowed, it gets easier.

[eyeguy21]

In regards to the zones, what usually happens is that the lens is seperated into 3 zones.
Zone 1 is the area in the centre of the lens and is 35mm in diameter.
Zone 2 is the ara outside of this, up to 5mm from the edge and Zone 3 is the outer 5mm edge.
In each of these zones you would have permissable defects that would be allowed. Defects are rated on the size and brightness of the spot and also length and width of scratches.
It all gets a bit complicated, but once you know what is allowed, it gets easier.

I've never heard it explained this way but it makes a lot of sense. It's funny how things all start to fall into place with just a simple explaination. What you're saying is that if you have a small eyesize like 45-47 and the Rx is a simple sphere, it really wouldn't be an issue to use a lens that has defects in the 3rd zone. I think that aligns somewhat with what MikeA said in his earlier thread regarding the use of 2nd's.

[IC-UC]

What you're saying is that if you have a small eyesize like 45-47 and the Rx is a simple sphere, it really wouldn't be an issue to use a lens that has defects in the 3rd zone. I think that aligns somewhat with what MikeA said in his earlier thread regarding the use of 2nd's.

Pretty much. Try to achieve some level of consistency in the labs by everyone aligning to one set of rules. Also makes it less of a chore and saves time thinking about whether to pass or reject a lens that has a small defect.