Re: [ATM] Reverse engineering a lens.

[Richard <cnc@cncservo.co.uk>]

Hi Thomas,

Saturday, September 10, 2005, 12:57:18 PM, you wrote:

TJ> Just a quick question (with a possibly not so quick answer;]) how would
TJ> I go a bout reverse engineering a lens, all I have is the OD, edge
TJ> thickness, FL and a guess at the glass. How would I deduce the curves?
TJ> One lense is a double convex the other is a negative meniscus.... Not a
TJ> lot to go I know, so any suggestions? I have asked the vendor if they
TJ> can get the ROCs for me, but I'm not holding my breath.

Can you find the centre thickness too?. If so, you could
construct the lens in CAD. As three points define a circle, you
will find the radii by telling the CAD to draw a circle through
the three points (top 'corner', vertex, bottom corner). You can
do that for both sides. Now you know the radii and the focal
length, you can work backwards with the Thick Lens Formula to
find the refractive index. Presuming you know the wavelength at
which the focal length was measured, you should then be able to
find the glass type.

-- 

Best regards,
  Richard in the UK
  

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