Re: wide-field beam expander?

Adam wrote

"I admit that even high-end models have some aberration near the edge
of the field, but since he is only using a 1mm sub aperture of a
roughly 3.5 mm exit pupil, I would think that should improve things
considerably. "

While it is true that the spot size is dependent on the ray bundle
diameter for field aberrations, it may not be true that using approx.
1/10 of the pupil will result in 1/10 the of the full pupil spot size
and this assumes that the spot at the scanner is _exactly_ centered in
the eye-piece pupil.

"The same is true with f-theta lenses. There are many of these lenses
out there for all sorts of purposes, and a lot of them have nowhere
close to diffraction-limited performance."

I have not encountered any f-theta lenses, from quality vendors, that
do not approach or exhibit diffraction limited performance over their
entire angular range. My experience is that a quality f-thetat lens
_will_ provide diffraction or near diffraction limited performance over
the full angular range of the lens capability. After-all, the intent is
to produced as many resolvable spots diameters over the scan extent as
possible. This true of image scannnners and laser machining scanners.
Most commercial f-theta lenses will specify the calibrated focal
length, the scan acceptance angular range and the expected spot size
for a properly formated bean distribution at the entrance pupil as well
as the number of resolvable spots that can be created. This is
fundamentally limited by the space band-width product of the lens and
then degraded by the quality of the design and its fabrication. Also
note that the long focal length f-theta lens will probably use only a
fraction of its angular range.

The good news is that you will be able to find specifications for the
lenses (for a single wavelength collimated laser) that will be
difficult if not impossible to get with the rifle scope. So the rifle
scope represents a lot more "buy and try" development than the f-theta
lens approach will.

BTW, I have designed and sold f-theta (and ultra-high angle) scan
lenses in the US and Japan. Their design is relatively straight-forward
and many patent files exist that would allow Brett to model the relay
before amking any purchase decision (using ODP or the 90 trial version
of SynOpSys).

Best Wishes,

Jamie

James A Carter III
James Carter Optical Consulting
http://www.jacarter3.com

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