Measuring frame ED

[Spex]

Any suggestions on an easy quick way to measure frame ED's. I know you can just measure diagonally across the lens area but I was hoping someone had a simple way to measure a little more accurately.

Do they make a guage that has circles that go from say 30mm out to 70 or 80mm that you can lay the frame on to get a more accurate reading?

TIA!

[JRS]

Measuring 'diagonally' across a lens (or frame) is NOT the effective diameter. The LED = the longest radius times 2.

Depending on the shape, mis-measuring (the diagonal method), and sending this information to a lab for uncut lenses (plus powers) can result in some unexpected edge thickness.

[Alan W]

Yo....SPEX!

Sadler makes an inside caliper. The same caliper has jaws that measure the outside, ike of a lens. Nice instrument.

[Alan W]

JRS . . .

Hi, Buddy. It's been a while. Hope all is well and you're learning to speak better french.

Ya know....when I was in school . . . yeh, way back then, our prof said that the EDX was "estimated diagonal measurement."

Now, who am I to argue with the likes of John Archer. But, it seems that his definition of EDX falls in line with yours a bit better.
I was never comfortable with effective diameter. But, then I was never comfortable with BVDs one size too small, either!

D'dum, dum!

[Wes Trayner]

The ED or Effective Diameter cannot, easily, be measured with a ruler and the frame since in all but round and pure oval frames, one of the componenets of the ED is outside of the frame. A hard way to do it would be to trace the lens on a piece of paper noting the 180 line. Draw a box around the lens drawing with the top and bottom lines being parallel to the 180 line and the sides being perpendicular to the 180 line. Draw a line through a point half way between the sides parallel to the sides and another line halfway between the top and bottom lines parallel to them. Measure from the center cross created by these lines to the farthest point away on the edge of the lens. This distance, multiplied by two, is the ED or the smallest circle that the lens will cut out of. Better still let the frame tracer figure it for you.....

[CME4SPECS]

The easiest way to measure an ED is to put a 180 line on the lens and find the geometric center, by centering the lens vertically and horizontally on a box-o-graph, put a dot at center and measure to the furthest point. Double that amount and you have your ED.

[Spex]

Originally posted by Wes Trayner
.......Better still let the frame tracer figure it for you.....

I'm sorry some of us haven't been able to afford stepping up with the big guys & the new fangled equipment!!

Maybe this could give me something to look forward to!

Thanks for the info!!

[Spex]

Originally posted by CME4SPECS
The easiest way to measure an ED is to put a 180 line on the lens and find the geometric center, by centering the lens vertically and horizontally on a box-o-graph, put a dot at center and measure to the furthest point. Double that amount and you have your ED.

Thanks! This is a great suggestion. I think this will work out great!

One of the main reasons for asking about this is that the labs are sending lenses out either too thin or too thick. Their reason is that we didn't give them the frame's ED. Some of the "patients own" frames don't have the dimensions listed anywhere we can find them, ie. Frames book. Or we cannot find frame name or manufacturer on the frame itself. So we have to take our own measurements. These aren't very accurate sometimes.

Now that I have some suggestions of how we can take some "close" measurements for the lab, we can help them do a better job for us.

Thanks again!

[Duane Metcalfe]

ED measurements

ED is acquired by adding the eye size (True BOX width, NOT from/close to the 180 line) + 2x's the patients monocular PD. This will give you the minimum lens blank size to use. Some of us add a little fudge factor to accomodate idiosyncracies from the lab doing surfacing.

hope this helps...

Duane

[Wes Trayner]

Duane,

Your formula is going to get you some pretty thick plus lenses from your lab if you are ordering uncuts. Your formula works for determining an approximate stock single vision lens blank size for a given frame. An easier method of guessing the ED of a frame, other than an oval or round frame, is to add about 4 - 5mm to the "A" measurement. Ovals or rounds the ED is about the same as the "A". By the way, the ED is NEVER smaller than the "A" or the B" measurements. Many lab software programs use something like this when measurements are not supplied. "Frames" publishes the ED of most of the frames listed in their publications so you could look there also.

[gebe33]

Hi Tia,
I wouldn't get too hung up on measuring the Ed. Measuring across the major diamention isn't the same as the Ed but would be close enough. You can add a millimeter if you want. This should fine for your lab needs.
Tom

[Duane Metcalfe]

ED measurement

H-m-m-m...too thick for PLUS lenses. Let see if I understand my math.

50 mm true box A measurement (measured where lenses come closest together as a starting point, finishing at the extension of a line from the widest temporal point of the shape while mm rule is held parallel to 180 line...not on 180 line unless that is where the widest point is...ala true round/oval/square shape.
20 mm true bridge measurement (where lenses come closest together)
32 mm monocular PD (64 mm total)
50+20=70
70-64=8 (or 2X's the monocular for this eye)
50 (A-size) + 8 (2X's monocular = 58 mm.

Needed explanation is in order here: 50 mm lens covers the width of A measurement...add 4 mm for initial decentration, if not grinding prism for it, but these are stockers, right?. Add another 4 mm for the amount you lost sliding the lens for decentration, otherwise your gonna have a big empty place at the temporal edge, assuming the OC will be placed on 180 line, not above or below, cuz then ya gotta figure that into the equation.

The requirement is 58 mm w/ '0' mm edge thickness...now, go pull a stock 58mm lens in whatever index you need. And, you did want these with the 'thinnest edge possible', didn't you?

Personally, I'd grind a lens w/ or w/o decentration prism for this PLUS Rx.

Back to the original ED question...if you can't figure 2X's the longest diagonal from the intersection of the boxed shape, then true A + 2X's monocular PD will get you closer than adding 1-2 mm to a 180 line measured A figure...plus a fudge factor (if inclined) for the discrepancies already noted.