Re: [ATM] Reverse engineering a lens.

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Thomas Janstrom wrote:

>Hi Richard etal,
>
>Well I now have the lenses on hand now and I can give the ROCs of all
>surfaces, however I have found a problem with some of the supplied data
>for the negative meniscus, to be detailed with the measured data below.
>So here goes.
>
>Lens one (now know as L1898, seeing as this was scribbled on the paper
>it was wrapped in.)
>Double convex, not iso. 
>Diameter 138.45mm (.5mm bevel on both sides)
>FL 525mm
>ET 5.0mm
>CT 13.595mm (OSLO LT derived)
>ROC surface one 454.247mm
>ROC surface two -679.712mm
>OSLO LT's best guess at the glass is Schott ZKN7 (matches stated FL to
>with in .125mm) 
>
>
With D = 138.45 mm, R1 = 454.247 mm, R2 = -679.712 mm, and
t(edge) = 5.00 mm, I come up with t = 13.84 mm.  How does
the bevel affect your edge thickness measurement?

Those are pretty accurate radii. To get that accurate, you'd
need full diameter sagitta measurements (assuming you're using
a spherometer) on the order of  0.01 micron. What diameters and
accuracy do you have?

With t = 13.84 mm and the f.l. = 525.0 mm, I get a refractive
index at the measured wavelength of 1.520808.  One quick question
is, "at what wavelength"?  I've seen some companies use the d-line,
some use the e-line;  Newport Glass, for example, actually
supplies their data for the C-line.

>
>So there we have it the "ground truth data". Now although I'm writing
>this on the morning of the 26th I won't get to send it for a couple of
>days as my phone line had a meeting with a grass fire and came off
>second best....
>
>Clear Skies, Thomas Janstrom.
>www.tjanstrom.com
>www.norsewines.com.au 
>
>
_______________________________________________
ATM mailing list http://www.atmlist.net/