Re: [ATM] Reverse engineering a lens.

[Jarvis Krumbein <jkoptic@juno.com>]

Sorry Richard but this will not work.  I can come up with an infinitely
large family of lens that are double convex but have different radii for
the two surfaces that are possible using your CAD method.  This will work
for a plano-convex but you would still need more information to use this
method for a double unless both surfaces had exactly the same radius.

Jarvis Krumbein in Vaughn Washington <jkoptic@juno.com>

On Sat, 10 Sep 2005 19:14:20 +0100 Richard <cnc@cncservo.co.uk> writes:
> 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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