Re: Shimming a triplet - 3D camera

[T3D Sam Smith <sam@xxxxxxxxxxxx>]

Hard Hearted Sam thanks warm hearted John for his excellent reply to my
probing.  Ed can rest easy now, I won't drive him crazy.

>> I want to know exactly the procedure. Let me give an example 
>> this time.
>>
>> I have one lens that is 45mm in focal length and one that is 
>> 47mm.  How do I make them match? Do I change the 45 to 47, or 
>> vice versa?  How do I do it?  How do I know how far to shim it? 
>> I'd even accept formulas on this one.

>Sorry, insufficient data to provide complete answer.

I expected that. To me the most complex part of the average camera is not
the shutter but the optics. How do you measure the power of a negative
element anyway?

My original interest in this issue was because I've got an old Ontoscope, a
medium format stereo camera of French design. It originally had Tessars, but
I picked it up with the middle elements missing! I have since substituted
Agnars, which took a little shimmying to accomplish. The results are good,
but the focal lengths differ slightly. My suspicion now is that I may have
misspaced the elements.

Agnars have front-cell focussing, but it's the first two elements that
focus, not just the first, which makes me suspect that you could move the
rear element instead of the front element to achieve the same effect,
changing the focal length.

Any thoughts?
Sam


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End of TECH3D Digest 38
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