Re: [ATM] Reverse engineering a lens.

["Thomas Janstrom" <tomjan@ozemail.com.au>]

Richard(s) etal,

These are surplus lenses so the info available is very scanty indeed.
What I have gotten so far is enough to get me currious enough to think
about buying them, if only for the glass.

Ok here is what I have.

Lens One.
Diameter 138mm
Center thickness (CT) @9mm (it has a centeral perforation so this is a
scaled measurment taken in the hole from a photo.)
Edge thickness (ET) @3.5mm (again a scaled measurement)
FL +540mm (biconvex)
Glass strongly suspected to be BK7

Lens Two.
Diameter 138mm
CT @7mm (same deal as for lens one).
ET @3mm " "
FL +525mm
Glass strongly suspected to be BK7

Lens Three.
Diameter 136.5mm
CT ?
ET 19.05mm
FL -800mm (negative meniscus)
Glass strongly suspected to be BK7

So there you go that’s all I know at present, but the price is
reasonable so I might just buy these and see what they are like in the
real world, photos are ok, but glass in the hand is OH SO MUCH better.

Clear skies, Thomas.
www.tjanstrom.com
www.norsewines.com.au 




-----Original Message-----
From: Richard F.L.R. Snashall [mailto:rflrs@rcn.com] 
Sent: Saturday, 10 September 2005 10:51 PM
To: Thomas Janstrom
Subject: Re: [ATM] Reverse engineering a lens.


Thomas Janstrom wrote:

>Hi all,
>
>Just a quick question (with a possibly not so quick answer;]) how would

>I go a bout reverse engineering a lens, all I have is the OD, edge 
>thickness, FL and a guess at the glass. How would I deduce the curves? 
>One lense is a double convex the other is a negative meniscus.... Not a

>lot to go I know, so any suggestions? I have asked the vendor if they 
>can get the ROCs for me, but I'm not holding my breath.
>
>
What happens when you try the GSUM tool, plugging in the aperture and
f#? After the initial design, you can force the edge thickness to what
you want and then continue optimization to the end; it will keep the
edge thickness until you start another design.

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