Hello everyone. This is my first time posting on this board. So please be patient with me. My question is about exceutive lens. How do you go about finding or should I say determing where the center is. The gentleman that showed me has retired now. And I know there has too be an easier way of doing it. I wish I could explaing how he taught me. But I just didn't get it. We don't have too many of these. I just know there is an easier way than his way. Thanks for any help that you can give me
Executive lenses are difficult to grind and fit properly, but with the trend toward smaller frames it is easier to fit them properly. Many labs have ignored the near vision and ground the upper portion to get distant PD correct, letting the near fall where it may. The obvious down-side of this is horizontal prism in the reading portion that must be adapted to by the wearer. With larger frames, this is sometimes the only thing you can do. But if the distance PD is gound where it should be, you will be able to spot the distance PD and the near PD and lay out both in the proper place. My recommendation is to disuade the customer from the exec lens style. They are thicker than a D35 or D45 and are ugly. Easier said than done though.
You should examine the Rx to see if the distance is more important than the near (higher power) and make a choice which one will be correct in the frame. Then lay out the PD accordingly. It is a compromise situation. I'm thinknig that the exec lens will go the way of the dinosaur in the near future. Their time has come to an end.
shutterbug
With your question, are you talking about in the grinding process? (layout)...Finding it afterward is simple..it's where the mires cross in the lensometer :)
The majority of Elines are on center, they do have some oversize decentered blanks still out there but the vast majority of the time you will be using the 38 mm and 71 mm blanks, when you lay it out center up the blank and whatever information you loaded into the software for OC in the 90 degree merridian.. you will see no place in the software to place a "in" and "down" ..only down, since you technically have no near PD their is no "in" decentration in the reading in layout.
I don't agree with shutterbug a 100% on the lens not being able to be processed readily, E-Lines are really easy to process, and you can use prism thinning to help with the thickness of the upper portion of the lens. I do agree with trying to see if anyone wanted to try out a 35, but ft45's are a nightmare for these guys that have worn E-Lines for a gazillion years.. they are used to a recessed add now it pops out and they come back with all kinds of complaints..reflections off of the seg lip, or they are not used to it and chip the heck out of the seg.
For certian things you can't beat an E-Line, and it may be a few more years before they discontinue it, we still have a large portion of the older section that wear them..when all the baby boomers that we have crammed into PAL's get further up in years than the E-Line will become a lens of the past.. still think we have another few years to go before they stop popping them out..
I think you might want to clear up what you are asking when "locating the center" ...
Jeff "shoot even I have a pair of them I like to use for certian things" Trail
bzzt
An Executive-style lens does indeed have a Layout Reference Point with both a lateral and vertical location; laterally, it's the thinnest point on the ledge, which is usually (if not particularly accurately) located by viewing a vertical line through the blank, and spotting the point along the ledge at which it does not "break".Jeff Trail said:
you will see no place in the software to place a "in" and "down" ..only down, since you technically have no near PD their is no "in" decentration in the reading in layout.
I don't know which surfacing program you are talking about Robert, every one I have ever seen is based on cutting on center in the layout so they do not even have a place for you to key in a in/down, say as a FT..where you might enter i.e. 5/5 than you lay it out 5 in 5 down.. while on an E-Line you just key in the down and block on center..you would have to have some type of reference point for the software to figure from where the seg line is located and where you want the optical center to end up in reference to the seg line and taking into consideration the frame measurments and pupilary distance.
I think that is where most people tend to run into problems with an Eline by NOT cutting it on center..I think that might be one of our problems (wholesale) we have to many people who are walking around with printed tickets and do know the mechanics and the physical part of what all those numbers mean... you would be surpised by the number of labs where I have been called into as a consultant and they had no clue what all the things really meant or how to manipulate the programs to make the lens come out a certian way, always a few (well most often) but they feel so overwhelmed they are giving up all over the place with optical "burnout" :).. no wonder breakage is running crazy through out the industry on the wholesale side..I've been in labs where it has been running in the high teens and even a few in the low 20% range!! .. the old B&L guy who taught me the basics would be spinning in his grave..
As you know we are getting more and more into the higher end technical materials where just entering things into a program and walking around with a ticket is eating up profit left and right in labs.. you better know WHAT each peice of equipment is designed for, you better know HOW each piece should be running in true calibration and you better be SMARTER than your equipment or you are in BIG trouble :) What are you doing answering a post anyway you are supposed to be tossing the bones by now :) .. don't tell me you are in Vegas and spending time on the computer!!.. not with all the trouble you can get in there..
Jeff "sometimes optics is a real pain in the..hmmm eye" Trail
I agree with Shanbaum on this. The near does have an Optical Center. Execs are very misunderstood.
The best article that I have ever seen on how to process an Executive was written by Ralph Drew about 27 years ago and appeared in the Optical Index.
You can also find the information in Understanding Lens Surfacing written by Clifford Brooks Chapter 6.
I personally use the horizontal line method of lining up the near center and the distance center. This is very important as I usually use Sola's Decentered E-Line which has a seg inset of 3.5mm.
I use Omics software and I have a choice of grinding prism for decentration or laying it out the old way with the overhang. If I use this method on a small frame I definitely crib the lens.
Orcolite at one time had a decentered Executive Trifocal which I processed the same way.
The way I processed it depended on how much blank I needed. I also processed the lens decentered and ground prism for the distance PD according to the inset when I was using RXPII.
Jerry
Okay Jeff and Robert, you guys tell me if this technique is right or wrong.
The way I was taught to layout an Exec for surfacing was by holding the lens over a piece of graph paper. I used a vertical line as a reference mark and moved the lens side to side horizontally until the vertical line on the graph paper appeared to be passing through both the distance and near zones with as little deviation as possible passing through the ledge. I spotted the lens at this spot and used that as a reference mark for surface layout and blocking.
Yup
That's exactly correct, though any convenient vertical line will do - that is to say, you don't need graph paper.Jo said:
Okay Jeff and Robert, you guys tell me if this technique is right or wrong.
The way I was taught to layout an Exec for surfacing was by holding the lens over a piece of graph paper. I used a vertical line as a reference mark and moved the lens side to side horizontally until the vertical line on the graph paper appeared to be passing through both the distance and near zones with as little deviation as possible passing through the ledge. I spotted the lens at this spot and used that as a reference mark for surface layout and blocking.
This spot once found when using the vertical line to find it should be inset to coincide with the seg inset when marking and blocking.
I usually use the edge of the work ticket to find this spot.
Jerry
My thinking would follow along Jeff's reasoning.The executive bifo is processed by centering the blank and grinding prism if needed. The prism will move the distance center in the correct position; however, the near does not always follow.
We do use decentered execs and if the method described by Shanbaum is used,we would cut off a portion of usable lense blank.An Executive-style lens does indeed have a Layout Reference Point with both a lateral and vertical location; laterally, it's the thinnest point on the ledge, which is usually (if not particularly accurately) located by viewing a vertical line through the blank, and spotting the point along the ledge at which it does not "break".
Joseph Felker
AllentownOptical.com
OK, all you may have a heart attack :) BUT everyone is "right".. to some degree.. it is going to depend on the lens which one is going to need to be applied, you have a decentered E-Line grinding on center is not the way to do it, if you have one that is on center say as in SOLA's 68 mm blanks than grinding on center works all day long and it is un-needed steps to center it up,, you have a layout marker that has grids you can use to speed that along..
I see and understand everyone's point and I guess if I was not experienced in a lab if I was looking at this thread it might look like we are talking about a "right way" and a "wrong way" when all of them are used in processing an E-Line, the tricky part is understanding WHICH process is needed on what type blank and HOW to use that process :)
One of the main culprits is that if anyone got into the lab's in the last 5 or 8 years (might even be a little longer) the trend of SMALL frames have been rolling and grinding those 68 mm on center E-Lines work probably 20 to 1 on having to use an over sized decentered blank..so a lot of lab guys don't or have not been taught the "how and why" when it comes to grinding an over sized blank..I just hope people reading the thread who "lurk" understands the difference and how we come to deciding which and what process we go through.. is that better :)
Jo,
You were taught correctly, and I'm sure that same person even taught you how to use a protractor to do layout..of course the majority of layout markers have the graphs that can save you all that time..but understanding the basics does come in handy..
Jeff "gee everyone is right..depends on the design" Trail
That's true. However, we were much more advanced on the finishing side of things. We had a 3M blocker that was basically a blue box the length and width of an index card and probably an inch tall. It had a foam cutout that you put the leap block in and a toggle switch that turned on three layout lights along a 180 line. You held the lens, front down, over it and attached it to the block by pushing the lens down by hand. Made the CS-7's and AIT's look advanced. Who would have thought that a decade later we would be using actual images of lenses and segs to lay out and block lenses.Jeff Trail said:
Jo,
You were taught correctly, and I'm sure that same person even taught you how to use a protractor to do layout..of course the majority of layout markers have the graphs that can save you all that time..but understanding the basics does come in handy..
Jeff "gee everyone is right..depends on the design" Trail
Jeff,
When you wrote about thining down the top, is it basically the same process as prism thinning progressives?
Jo,
Thinning a E-Line can be a tricky thing, but yes just like a PAL.. the biggest thing you have to watch out for is cut out and power, if the frame size/PD lets you get by with it I do it all the time, especially nice when we have to do rimless jobs and drill mounts.
Taking the RX you do not want to push that OC to much though because it will reduce the visual acuity.. you weigh the plus and minus on about every job but once you get the hang of it it is not really all that complicated.. you also need to take into acount power difference and how the power is effected away from the OC..since we are placing equal amount of prism it would be neutral.. but in theory it looks good on paper in our visual system..well thats another story.. take a -1.50 -.75..and a -.25 -.75 ...check it at different erea's along the same meridian and you'll see how the power checks different at the same points along the line because of the power..this is just one of those things where you kind of pick it up as you do it.
I will say it does make a more cosmetically appealing lens (as far as you can make an E-Line look good:)) It is worth tinkering with though..especially in the high plus RX's in an Eline..
Jeff "just a little ol' tinker'er at heart" Trail
Another easy way to find the center on an exec is to reflect a flourecent tube light off of the celing perpendicular to the seg line.
The image of the bulb on the distance portion will be in a different spot than the near. Tilt the lens back and forth until the image lines up. That is your center.
mrba
While we're on the subject, if an Executive-style lens is not blocked properly, an excessive amount of horizontal prism-imbalance at near can be induced. Misuse (or abuse) of these lens styles was pretty common in the past, even though AO introduced a ton of papers on the proper way to process them, and I suspect that many people are still unaware of the correct way to handle them.
Best regards,
Darryl
RTPERRY:
I just wanted to say " welcome to Optiboard" !
I hope you will gleen a lot of information as I have ...
Happy New Year!
Karen
Heres another thought on Execs.
Don't use them they are ugly!!!:)
Flat 45 way better, just as functional
mrba
executive lenses should be extinct!!
one cannot plot both hear and distance oc,s properly, you hit a happy medium and hope for the best
I would just like too say thanks too everyone that replied too this. We only get these about once every 3 or 4 months. They are such a pain. And you are right they should be extiinct. And I would like too say this place is awesome!!!!. I am glad I have somewhere too go if I have a question. Keep up the good work! :) :)
For many years I was an Executive lover (what an expression). Originally they were sold and introduced as the lens with no image jump by American Optical in the 1950s. This would indicate that your optical centers would coincide on the line. I have gotten used to my ST35 and like them as well and wear my progressives only during cocktail parties when the scotch obliterates the distortion.:cheers:
mrba, "a FT-45 is way better". well, one problem there is that there is a lot of ledge reflection up into the pts eyes, to me a 2.50 add in a ft 45 is ugly too....
Actually, believe it or not, you can get the distance and near optical centers exactly where you want them with executive-style bifocals. They are a very flexible lens design, though they often result in thick lenses -- particularly in plus powers.one cannot plot both hear and distance oc,s properly, you hit a happy medium and hope for the best
Best regards,
Darryl
Ok, you have sparked my curiosity Darryl, how does one do as you have stipulated?
You would start by marking the optical center of the segment. You can do this by moving the lens laterally across a vertical line or crosshair, and marking the point on the ledge at which the vertical line is contiguous across the segment and distance portions. This is generally the thinnest point on the ledge.Originally Posted by mrba
Now, if you want to have the segment optical center at the correct near PD, as you would with a flat-top bifocal, you would just treat the point you marked as the center of the segment for the purposes of surfacing layout. You can also move this point in or out from the desired near PD in order to produce a resultant reading optical center at the actual near PD. For instance, you can over-decenter the segment centers of a pair of plus lenses in order to produce enough base in prism with the bifocal segments to neutralize the base out prism produced by the distance portion during near vision. Similarly, you can also induce horizontal prism at near that differs from any prism in the distance portion for prescriptions that require different amounts of prism or prism just for near vision.
This is something that you wouldn't generally do with a flat-top bifocal, particularly since it would restrict the binocular field of view at near. However, this isn't a concern for executive-style bifocals, since the segment extends across the entire lens blank.
Best regards,
Darryl
I suppose by the ugly standard they are all ugly.mrba, "a FT-45 is way better". well, one problem there is that there is a lot of ledge reflection up into the pts eyes, to me a 2.50 add in a ft 45 is ugly too....
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote
Bookmarks