T3D Re: matching lenses

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>A couple weeks later I had the pair which was
>measured at 123.2mm, which was farther from 120 than I would have expected.

  The advertised FL of that lens is 120mm
but they may in reality all be centered
around 124mm +/- 1%.  That's why camera
lens FLs are usually nice round numbers
even though when Pop Photo or others test
them they are several mm away from that.

  So I don't think you can tell what
the manufacturing tolerance is from that.
You'd need to see the results of lots
of measurements.


>I have also matched medium format cameras,
>and even with identical cameras have found
>it a challenge to get 2 to match. I had to test 5
>Yashicamat 124G's to get a pair that is pretty close.

  I tested a 5 Rikenon lenses from late 50's
Ricohmatics and Diacords. I had four that
were pretty close to each other and one (with
a much older serial number) that was over 1 percent
different.

  My best pair (that I put into my Stereo Ricohmatic
225) were about 0.3% different in FL. Doesn't
sound like much be when you put the slides in
a mount objects at the top are cut off differently
in L and R if you line up the bottoms. So I shimmed
on lens out a bit and got the image size difference
down to 0.13%. This means the two lenses don't
focus at quite the same point. But I tested them
wide open (f3.5) and found about a 6" focus difference
at 7 feet. At normal shooting apertures of f11 and up
I don't expect it will be noticable.

  Info on the above on my web page (Stereo Ricohmatic 225
link):
http://www.angelfire.com/ca/erker

Greg E.


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End of TECH-3D Digest 503
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