Kryptok Blanks Cheking Method.

[sandeepgoodbole]

In India,Glass (Crystal) Kryptoks hold 80-90% of the market of Bifocals.
The addtions written on the Blanks and the Covers by the manufactoresr many a times come out errornus after finishing.There is no way known over here which can detect the Accuracy and irregularities in side the
Unfinished Blanks. Can anybody tell me if they have some sort of
Non Destructive Testing methods, may be X ray , Ultra sound or infrared which can test unfinished blanks.

[Rich R]

How about using the lensometer to check add power, if the semi finished blank is not to opaque, just check dist power first than the add, subtract first reading from second should give accurate add power.
Rich R

[shanbaum]

It must be the case that the blanks can't be read through a lensometer, or there wouldn't be a problem, would there? If sandeep didn't know about lensometry (or how to check lens power without one, which also requires transparency), how would he know they're wrong after they're surfaced?

It's an interesting problem... I wonder if some method couldn't be devised by measuring the jump of a narrow beam of light (as from a retinoscope) as it crosses the edge of the seg? It might be possible to measure that on the back surface, even if it's only translucent.

Maybe this will give Darris something worthwhile to do...

[Steve Machol]

If the back surface is too opaque, you might want to consider grinding and polishing them just enough to create a clear optical surface. You can then check the add powers and repackage them accordingly.

The other alternative is to consider buying your lenses from a more reputable lens manufacturer.

[sandeepgoodbole]

Originally posted by Rich R
How about using the lensometer to check add power, if the semi finished blank is not to opaque, just check dist power first than the add, subtract first reading from second should give accurate add power.
Rich R

Blanks are Opeque over here.Lensometer, neutralization are the tools and method to chek the transperant lenses.
Shanbaum is absolutly right. He got my quarry exactly .& moving in right direction.

[chip anderson]

Can't add radius vs. base radius be checked with a lens clock?
I assume at least one side (the one with the add) is surfaced.


Chip.

[shanbaum]

Originally posted by chip anderson
Can't add radius vs. base radius be checked with a lens clock?
I assume at least one side (the one with the add) is surfaced.


Chip.

Note his location - India. These would be fused glass multifocals. Remember those?

[sandeepgoodbole]

Originally posted by Steve Machol
If the back surface is too opaque, you might want to consider grinding and polishing them just enough to create a clear optical surface. You can then check the add powers and repackage them accordingly.

The other alternative is to consider buying your lenses from a more reputable lens manufacturer.

That is the way we are currently cheking.But, now we are expecting to trace Bin Laden in the Opeque Afghan thru a satellite having resolution of 1 meter, so why cann't we find out the power in side an near absolute opeque bifocal blank which is within half a meter from our eyes?

Cost reputation of supllier cannot esacpe the same process as followed by us. More over, that can be a business alternative , not a process development.

[John R]

The best way would be to surface a sphere on the back of the lens with the same curve as the front, you may get away with a short polish so you can read it on a focimeter. But remember that to check the add power you need to read the lens power from the back, turn the lens over and read the add power from the front, the diffrence is the add power.
btw are these round segs or D segs. I have not seen a kryptok lens packet for years, made by BAO or UK opt if i remember correct.

[shanbaum]

Kryptoks are round segs. I think it may have been American Optical's trade name. I do recall someone objecting once upon a time when I referred to plastic round seg blanks as "kryptoks" - they could only be glass, I was told. Perhaps one of the really old guys (or Darryl) knows the rest of the story.

[shanbaum]

I wonder if it would be possible to do, in effect, a retinoscopy on the blank? One could thereby measure the power through the distance and through the seg, the difference being the addition? Would the (presumably) curved back surface, which would have to have sufficient regularity to reflect or display the beam, affect the result?

Perhaps someone who's actually, y'know, done a retinoscopy could comment.

[David Wilson]

John made an important point but may have got it a little wrong. When you check the add of any bifocal (fused or one piece) with its seg on the front you need to measure the seg front vertex power (with the front surface against the lens rest) and then the distance ALSO FRONT VERTEX. The difference between the two front vertex readings is the add. John's message may have implied that you compare the normal back vertex power of the distance with the front vertex power of the seg.

Regards
David Wilson

[chip anderson]

Can't you put a lens clock on the add surface and the ajacent surface and calulate the difference?

Chip:cheers:

[shanbaum]

Originally posted by chip anderson
Can't you put a lens clock on the add surface and the ajacent surface and calulate the difference?

Chip:cheers:

Glass! Fused multifocal! Come on, man! Think back! The front surface of a fused multifocal is a continuous curve; the addition's increased power resulting from its being made of a higher index glass than the blank, into which it is countersunk.

I know - it was the 60's that did this to you, wasn't it?

I mean, the 1960's.

[sandeepgoodbole]

Retinoscopy type experiments can be carried out where path is absolutely transperent the light comes back to almost the same direction thru which is emmitted.These just cannot be performed as the extra thickness of the "Button" (Flint)is protruding on the (front) Convex Surface.The finish of the surface will not permit anything like Retinoscopy. I hope X ray analysis or CT scanning may be the process thru which the Geography of a Fused surface of rough Opthalmic Kryptok Blank could be mapped. May be two or three diamensional would give required accuracy. I have tried Front exposer on an Orthopedic X ray Film .I got white circles for Buttons and Darker areas for the Crown. Can we think of X ray retinoscopy? Can some body outrightly reject this possibility?If not, How it can be done?

[John R]

Reading you last post are you talking about blanks before they have had the seg surfaced ? If you are then i dont know a way to check them.
Would i be right in assuming that you have a load of blanks that need the front side finishing but are unsure of what power the add is.

[shanbaum]

That's what it sounds like, John - I thought he was talking semi-finished blanks, but it sounds as though the buttons haven't been ground down, just fused to the front. I'd say measuring the interface curvature would be very difficult indeed.

[sandeepgoodbole]

Sorry for not able to describe the problem to the required extent while posting itself. I posted it just because the answer may be a bit "out of the Trade". I do not think it is impossible. If some body can invent any such thing, the EYES of millions of , at least ,Indians will have a better specs. I wonder whether this sort of Scanning will also help detect Defects in D bifocal (Flat Top, as I have noticed some where on OB) Rough Blanks , which appear more popular in US. That is going to save a furtune to Blank Users.:cheers:

[John R]

Sandeep. Dont be sorry, all to often we assume things are as we expect. I have to say its been a good 15 to 20 years since i have seen a rough fused blank, we used to keep the odd few in as the blanks were much thicker than the semi-finished one's we bought, also saved having to stock 22 and 24 segs but what a pain it was having to try and match seg sizes :hammer: 30 secs to long and your 24 seg was a 22 seg and thats if you were lucky.
Ah the good old days, i don't miss them one little bit...........

[Wes Trayner]

Note to Robert Shanbaum: The Kryptok lens was a crown glass lens with a flint or lead glass wafer fused to it. The more modern versions of this lens are made with barium glass in the segment which greatly reduces the chromatic aberration that was the hallmark of the Kryptok lens. These lenses fell into disuse back in the late 50s and early 60s.

[harry a saake]

Wes is right in what he posted which is also why a plastic round seg cannot be reffered to as a kryptok. Also when Kryptoks were first introduced they were called invisible bifocals, as they were almost invisible, with the very thin line that the bifocal produced, which is also a lot of times a good reason to use them on your plus patients.

[chip anderson]

sandeepgoodbole;

Buy American!

Chip
:cheers:

[sandeepgoodbole]

Originally posted by chip anderson
sandeepgoodbole;

Buy American!

Chip
:cheers:

Sugesstion is welcome!! ButI want to know, if at all they know,how do Americans make sure that a Rough Kryptok Blank comes out the correct Addition and without any defects after the surfacing ? I want to rule out statistical probabilities of errorenus Blanks , and find out a method which could do a guarnteed Post Motrem of a Rough KT Blank without disecting it.!!

[rbaker]

We used to check opaque (fined surfaces) powers in the lensometer by first wetting them with water or if it dries too rapidly kerosene. It the inside surface is just a molded or cast surface, lots of luck.

[shanbaum]

Originally posted by sandeepgoodbole


Sugesstion is welcome!! ButI want to know, if at all they know,how do Americans make sure that a Rough Kryptok Blank comes out the correct Addition and without any defects after the surfacing ? I want to rule out statistical probabilities of errorenus Blanks , and find out a method which could do a guarnteed Post Motrem of a Rough KT Blank without disecting it.!!

Most American labrats have never seen a rough Kryptok blank ("rough" meaning a blank with a fused but otherwise unfinished button), much less have they had to worry about measuring one.