Matthew Hunt wrote:
On Wed, Dec 7, 2016 at 2:22 AM, Larry Colen<[email protected]> wrote:
In simple terms, the definition of infinity focus would be to have parallel
incident light rays. Divergent rays from a point source are closer than
infinity. One could probably set up a calibration unit with parallel light
rays using conventional optics. I suspect that a low powered laser would
also work.
In case it helps your googling, what you're trying to achieve is
"collimation" of light.
When I taught astronomical instrumentation lab, we achieved this on
the bench with a white light shining onto a spatial filter (basically
a pinhole), with the spatial filter located in the focal plane of a
Nikon 200/2.8 or 300/4 lens (which was "locked down" to infinity
focus). The light coming out the front of the lens was (reasonably)
collimated. If you picture parallel rays coming from a star on the sky
and being focused to a point on the sensor, it's exactly that, except
the light is moving in reverse.
Once again proving the adage that the fastest way to get the right
answer is to post the wrong one on the internet.
--
Larry Colen [email protected] (postbox on min4est) http://red4est.com/lrc
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