Re: wide-field beam expander?

Hi Jamie,

Like any other type of commercial optics, the quality of rifle scopes can
vary greatly in manufacture and design. Some will vignet at the edges of the
field and have noticeable aberrations while others will not vignet and be
very close to diffraction limited especially using a single wavelength and
limited subaperture. After all, there is about a factor of 30 difference in
cost between low and high-end models. 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.

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. There are also very good scan lenses for
critical applications, and your suggestion should work with the right
lenses. This did get me thinking about one thing: The microscope objective
is not an f-theta lens so the position of the spot will never be perfectly
linear versus scanner angle. However if you use a relay made from f-theta
lenses, it will be closer to linear than if you use a regular telescope as a
relay.

Another possible solution for Brett is to use a good eyepiece with very long
eye relief together with the appropriate focal length achromat. I am
thinking in particular of surplus military eyepieces I have seen that had
excellent images and maybe 60mm or more eye relief. I have not seen those
on the market for many years now though.

By the way, I agree that scanning the beam after expansion would be easier
in many ways, but then he would still need a 1X afocal relay to image the
pivot point onto the objective pupil in addition to a conventional beam
expander.

--
Adam Norton

Norton Engineered Optics
Optical design and systems engineering for Silicon Valley and beyond.
http://home.ix.netcom.com/~anorton/

(Remove antispam feature before replying)


"Jamie" <jacarter3@xxxxxxxxxx> wrote in message
news:1113919794.045965.53280@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> It certainly would be easier, cheaper and provide better performance to
> expand the beam prior to the scan mirrors. When scanning prior to the
> afocal relay, the scan range increases significantly and if you trying
> to achieve scan velocity (angular) by using small mirrors, then you now
> have to rotate them 10x faster to achieve the same characteristics at
> the microscope entrance pupil.
>
> Note that long eye relief may be a curse in disguise. The +/- 10 to 30
> degrees will probably create a beam foot-print that exceeds the
> eye-piece lens as the eye-piece and rifle scope probably vignet at the
> edge of the occular field of view (this eliminates some aberations in
> the design but appears only as a reduction in perceived image
> brightness to the human eye). As for diffraction limited performance,
> don't even think that a rifle scope will achive anything close to that.
>
>
> A 10x telecentric-afocal relay can be achieved by using two f-theta
> scan lenses (with flat scan fields) that operate back to back. Pick two
> with a suitable ratio of calibrated focal lengths and scan ranges and
> you can get what you want, probably off the shelf. This also provides a
> convenient image conjugate plane if you want to do any image processing
> or filtering.
>
> Just my $0.02...
>
> James A Carter III
> James Carter Optical Consulting
> http://www.jacarter3.com
>


.

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