Re: ATM : Additional Secondary for guiding ( was offcenter secondary)

[Andy Saulietis <iss@pvtnetworks.net>]

Jean writes,

>Reinventing the wheel here ;^)
>Isn't this the same as off axis guiding ??

Sort of, in that you use an annular FOV
to find guide stars. The difference
is that the tertiary mirror can be directed
away from the imaging field, simplifying the
design/use of the guide mechanism, which no longer
has to crammed in with the imager. It also
becomes possible to see the entire guide field at
low magnification making it easier to select guide stars.

The main disadvantage is that the focal
plane will be closer to the OTA, maybe
requiring a Barlow or relay lens to make
the guide field focus accessible. Differential
flexure can also be a consideration, between the
two secondary mirrors.




Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
505-687-3067 voice
505-687-3021 fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net